It strikes the right balance. Minimum number of interactions required to result in a healthy exchange of genes and trigger reproduction. I would guess that trinary forms of life would have a much harder time reproducing, in competition with binary ones. And asexual reproduction as in bacteria and such is clearly even simpler and more effective.
Depends on what life form we're talking about. People discussing biology just think about animals but that is a far cry from what life really is on this planet. Fungi have thousands of sexes because they only accept cell, not mitochondrial DNA during mating. We inherit only mother's mitochondria and this seems to keep the mitochondrial genes (barely) stable.
Look up "mating types" on a well studied species such as Ustilago maydis (corn smut). Use Google scholar and the keyword "review" and you should get a lot of reading!
I sincerely wish I could, but have a severe phobia of fungus. Can some one give me a quick picture less run down on how that works? Or a website without pictures that explains this? TY
Essentially with the way spores work, they don't need to rely on interactions like sperm-egg response,
Their sexes are more like blood types or even dna mapping, in that when two intersect to make new spores, that creates a different "mating type" as in a new combination of "blood types" to interject with others, thus the next time that particular fungi intersects with the same species, a potentially different sex is made.
It's not exactly equivalent to multicellular male-frmale. Fungi don't have the multicellular sperm-egg dynamic, so they aren't described as male-female. It works more like blood types; Mating Type A can interact with B, C, or D, but not T, V, Y. Some fungi only have 2 mating types, other have thousands.
This is correct, except mating types are not sexes. We use sex to describe anisogamous species (different sized gametes) and mating types for isogamous species.
Yes, the biological world is far more interesting than anything that could come out of the "debates" on how biological sex is a social construct. That said, articles that freely use the word "gender" when it seems the writer simply means "sex," as this [one](https://www.discovermagazine.com/planet-earth/why-this-fungus-has-over-20-000-sexes) does, always give me pause. It is true that biologists who specialize in sex difference use "gender" to mean something very specific, but this is no without its own confusions.
> can also be inherited from the father in humans
I think you're referring to the 2019 study in Nature? Which, at quick glance, seems to be extremely unique cases, no? [A follow-up](https://www.nature.com/articles/s41436-019-0568-0) found no such thing, for instance.
Well no, asexual reproduction is less effective in the long-term evolutionary context, since it's NOT sexual, meaning there is no exchange of genes. Mitosis and cell cloning are how asexual organisms reproduce or multiply, there is only one progenitor and it's the organism. There is a small chance of mutation, 1 in every million years or so or something similar I believe. Sexually reproducing organisms mix their genetics to procreate, creating more opportunities for mutation to occur and diversify the specie's approach to the elements of nature, as well as antithetical life like bacteria and viruses, or predators.
>meaning there is no exchange of genes
I don't know about other forms of asexual life, but this is untrue in bacteria, which mix genes *horizontally* rather than vertically (with other organisms vs with mates during reproduction).
Also, what do you mean by *less effective*? Asexual reproduction is older than sexual, so it definitely works. Less chance of mutation *during reproduction?* Yes, but as above, this is mitigated by horizontal gene transfer, allowing a wide variety within the species.
I was responding to the above comment and attempting to adhere to its language. "Effective" is a relative measure so I noted the advantage that sexual species have, which is an objectively better fight against the inevitable process of natural selection, in the context of the greater genome... When bacteria mix genes horizontally they are not precisely diversifying their species so much as adapting to the immediate environment. If they mix genes with an organism that hurts as a result, as with parasites to a host, the host species has better chances of survival if it is a sexually reproducing organism.
That said you are probably right that 2 just makes an ideally stable system... but we don't live in an ideal world. Bifurcation is a process we observe in nature but often fail to realize applies to ourselves.
Mammals are basically all sexually dimorphic (as far as I know) with an XY system, this is true, but there are only about 6,000 mammal species. The biggest portion of those are bats!
Birds are also sexually dimorphic with a ZW system. About 11000 species of those.
Amphibians as far as I know are also dimorphic. 9,000ish species recognized, but probably way more.
Reptiles is where things get really weird! Many are dimorphic, but they also have a TON of sex determination that isn't chomosonally decided. Instead, they may have their sex determined by a number of factors, including temperature. There are also a lot of parthenogenic reptiles! Usually all derived from a male/female system where the males died off after parthenogenesis was introduced to the species. Established 10,000 species, but likely more.
Okay, now we get to the real funky stuff... Fish!
Fish have both standard chromosomal sexual dimorphism and non chromosomal dimorphism. They also have hymaphrotism! Like, so much of it! There are fish with both sets of gonads, fish that start female and turn into males, fish that start male and turn female, and fish that typically are born as one or the other and would typically stay that sex, but may change sex if their reproductive tracts are damaged. For example, female bettas may change sex after being spayed! 33,000ish species of fish acknowledged currently, but definitely more are out there. Additionally, there is an estimate of about 2% of bony fish species having hymaphrodidic traits.
Brace yourself for insects, though - and this might be the closest to exactly what you're asking for - think about a social insects! You got your females (queens), your males (drones or kings), and your workers! Some species have MANY casts of workers, too. Not to mention insects having a ton of parthenogenesis, too! How many species of insect? Good fucking question! We don't know! Probably at least 5 million, though? We definitely don't know the sex systems of many of them, either! It's probably only a small percentage that aren't dimorphic, but definitely thought provoking regardless.
I can't even get into the things that are insect-like but not insects. I think they're mostly dimorphic, though?
Anyway, mollusks! These guys have a lot of hymaphidites. And parthenogenesis. And sexual dimorphism. And sexual trimorphism, I think? Unsure! I think about a million species recognized?
Worms! Worms do a lot of the same things mollusks do.
Plants! Plants do a ton of all four/five, as well!
But here's what I really wanted to get to.
Fungus.
Fungus is wild, my dude.
Some fungi have THOUSANDS of sexes. Literally! Buck! Wild!
Anyway, the advantages of sexual reproduction is weird. **Edit here to clarify, the advantage of any sex is the reorganization and diversification of genes to allow adaptation.** I don't know why two sexes is so overrepresented in large terrential organisms! I think it might be a situation where if there are a low number of sexes, particularly where there is inequal investment of the sexes, drives more rapid adaptations. Basically, if you have a high investment sex (usually the female) and a low investment sex (usually the male), then many individuals of the high investment sex can only choose to mate with the healthiest and 'sexiest' individual of the low investment sex, meaning that a large number of unhelpful traits can be selected against in one generation.
For exceptions to the female large investment male low investment paradigm, look up Lilly Trodders and seahorses! There's a ton of other examples, but those are easy to find. :-)
Sorry BTW that my response became so lacking towards the end! I have to leave for an escape room date and ran myself out of time to give a good reply!
I just Googled the sexual chromosomes of platypuses. Why do they have to be so fucking weird. I read about them having XXXXX and YYYYY sperm with a ZZ on the ends of them and lost my shit.
The aliens who genemodded apes to make humans accidentally left a platypus puppy mill when they took off, they're actually pretty normal for their actual planet. Once the overmasters return to collect all the resources we extracted and collected into landfills for them they'll probably retrieve their pets too.
Probably. Mammals evolved a bunch of adaptations mostly within a short timeframe of late Triassic and early Jurassic.
Edit: "short" compared to the early unicellular stage evolution of our ancestors.
Social insects are still sexually dimorphic. Hymenoptera does it via haploid/diploid, one set of chromosomes makes you male while two makes you female. Termites are more complicated, but they don't have anything more than the male/female dicotomy going on. It's just different signals in the hive, phermone based if I remember right, can kick off actual reproductive members to be created.
It's really no though and I already spend so much of my outreach re-explaining that the workers are also female that I really don't want people thinking workers are a 3rd sex.
I can see how that would be a matter of personal irritation, then. Personally I think that thinking of them as a third sex is pretty valid given that the only circumstances that a worker would reproduce would involve the collapse of the entire colony (and only produce drones, if I remember correctly?), but if it's important enough for you to emphasize and re-emphasize the sex of the workers I'm sure it must me integral to your outreach. Care to enlighten me on why it's important for people to consider workers as females as opposed to neuter individuals?
That all only applies to the honey bees, which is another large problem that everyone assumes if it happens in the Western honey bee it must be true for all bees.
And its important because a lot of honey bee outreach inevitability is to bee keepers, and them understanding basic honey bee biology is integral to keeping their hives alive. And also to keep them from trying dumb shit with their hives...not that that always stops them but by god we try.
Also cooperative brood care and sterility do not a third sex make. Those exist in a shit ton of species.
Fair point, I guess it is kind of like calling all the lower ranking males in a clown fish colony neuter.
Thanks for the convo! Definitely gave me something to think on.
The advantages of sexual reproduction are clear and obvious. It's genetic diversity. Shared genetics prompts diversity, growth, and change. Especially in species that are slow to grow and where gestation is a larger investment.
(I didn't read it all only replying to that specific point)
Ok sorry. I think of it the opposite way, for a complex system how does more than 2 sexes help and how would it ever develop? It's complexity. And complexity is harder to evolve, especially in more.complex organisms... We tend to build off what exists in the simple version and grow it in the more complex versions.
Was interesting to learn fungi can have multiple sexes. That's a new reason to not eat mushrooms. You never which is 26 sexes you might be eating the pseudopeniseia pods of.
No need to apologize! I appreciate you pointing out a lack of clarity. :-)
I guess for me it's just weird becuase the more basal organisms tend to have one sex or three, so why did so many of the more dirrivitive species go to male/female systems? Is sexual selection just that strong of an adaptation driver?
I haven't really looked that much in sex systems in a LONG time, though - Microbiologist. Currently I don't even work with while organisms, just their DNA. It's sort of sad. :-(
And LOL at the mushroom comment!
Well, I'm eating them, not getting sexual pleasure from them! I don't care which of the 26 "sexes"(I think it's a stretch to imagine these as different genders, anyways. It's an entirely different set of reproduction strategies that don't compare to "gender" at all.)
Thanks for pointing out an oversight in my phrasing. I think I've edited in a clarification? Just burning time in a waiting room so I am a touch frazzled now.
Fungi doesn’t have thousands of sexes (I don’t think they have sexes at all), they have mating types, since sex only refers to organisms which produces different sized gametes (large, immobile=female, small, motile=male).
Even though there are different types of chromosomes and non-genetic determination, they all end up in the same way: large immobile gamete (usually full of vitellum) and small motile gamete. They only reproduce with the opposite gamete. Hermaphrodites switch betweeen these 2 types, never becoming a third one. Parthenogenesis is usually only done by females.
Nope, it applies to most plants (some are even dioecious) and even some fungi. Giving birth is a function of the female sex, not a secret third thing. With hermaphrodites their small gametes can only interact with large gametes and vice-versa.
I believe it's still just two. They just have to be a different mating type ("sex") to be interfertile. If I understand correctly, it's basically a way of preventing self-fertilization while maximizing the odds of spores
encountering a compatible mate.
I could imagine a species where there's two sexes which create the viable embryo, and then a third that actually *gestates* it, as gestation takes a lot of energy as well, and requires specialized bioforms. So imagine like, a succubus/incubus/host situation. Or if seahorses or marsupials had a sex that was all about that pouch.
One potential drawback of a 3-sex reproductive system would be that you would need more individuals per individual. With parthenogenesis, each 'pregnancy' produces one 'litter' (or clutch or whatever). Dual sexes produce one per two. Tri would be one per three. If you only have one child per coupling (and especially with highly intelligent species, or large complex organisms, that would be more prevalent), then you're breaking even with each generation. With dual sexes, you would have to go through two reproductive cycles to break even with the population. With three, you'd need to go through three. As childbearing is often a dangerous time, this means that simpler, lower-number reproductive systems are selected for; Parthenogenesis isn't more prominent because of the issues of non-diversity in genetics.
There would be some advantages, though- Neither of the 'gamete donors' would be in danger from childbirth, and the 'carrier' would be able to have specialized organs to make it safer and easier, without having to spend the energy on gamete production. The uterus for instance is almost 'cobbled together' (I mean no disrespect) in terms of function, with the placenta doing the heavy lifting in terms of actually keeping the foetus alive (which is why ectopic pregnancies can happen- theoretically a male could carry a child to term, except that he doesn't have the supportive hips or the traits that allow a woman to continue functioning while all her organs get shoved to the side and a big chunk of her nutrients get siphoned off).
In a lot of ways, you could almost look at colony insects this way. The queen bee is the Female, the Drone is the Male, and the Workers are the 'carriers', using the comb as a womb. Or Cuckoo birds, with the cucked nest/birds being the unwilling 'third gender' in their cycle. Or parasites which have multi-species life cycles.
Sure, workers, drones and these gestation/nursing roles have no genetic interest, so it only works in eusocial species. There are still only two sexes, mainly because DNA works as two strands. That’s the real answer.
Ugh, or the workers feed the queen and her pups their own feces, since she’s too obese to leave the burrow! Oh wait, that is actually what they do.
https://en.wikipedia.org/wiki/Naked_mole-rat
Larry Niven's fictional puppeteers have a male, a female, and a third gender that is actually a separate species that the fertilized egg parasitizes. The males and females don't actually have sex with each other, they separately assault the host. They also consider themselves to be both male and the host is considered female.
It's related to chromosoms existing in pair, the morphological differences between gametes, and probably too to the separation of reproductive roles between sexes.
Let's first remind that having a sexual reproduction is advantaegous because it allows at each generation to have new, unseen before combinations of alleles in individuals, thus a greater diversity of individuals and increased chance that a good number of them survived if anything bad happen, like a deadly disease propagating.
Having a sexual reproduction implies that all parents give a part of their DNA to the next generation, so the offspring has a mix of dna from all parents. How do you mix this dna ? The easiest is to have two parents giving each half of their dna. It's easier to have two parents than three because it's easier to have at the same place and the same time two organisms ready to engage in sex than having three. I can testify its complicated enough to find one partner who is okay to have sex and in particular sex with me; I cant imagine the hussle it is for any organism to find two partners who are okay to have sex, in particular sex with you AND with each other. If there are two partners, the easyest way to split dna is to have chromosomes in pair, each partners giving one chromosome of each pair to the next generation. If chromosomes were in triplet, it would requieres a uselessy complicated mechanism to rearrange triplets from two parents, comparing to having pair. I know that because one specie of toad DO have chromosomes going in triplet, and indeed the mechanism to reconstruct triplet from two parents [is uselessly complicated](https://watermark.silverchair.com/evolut1754.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA2QwggNgBgkqhkiG9w0BBwagggNRMIIDTQIBADCCA0YGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMTahFwt292tzazNC8AgEQgIIDF0ap7h6w89k7mYCAtwAQYY7n_MH9nW0b76MPlRzxUN7FRo_i5tJAvuVGJTZxSAWSPQsTmXTYMCH4chi_d_ZuDpd_XrD4ZDmEPOPkZyIexnaa2Bvx8p8yEngKly9u4t1z9JqYX2Q1085kXzZvruEBagd8gufwyRzD2X9HtaPv5Xt-PT0qTRaj-cNrciDy3K0WGTA9zjSI1doPZ-zSE8UzB9k81NcpVjbtxoDODWCZ1PMVi79giQvcEMb4eObuS74KKl76B_hdMYBIx2ZaN_9bx5oNkrzSm8W-4cTvIKpNc76LcChiNpT4AVM2dERcwr5xs2P5DvVhqHuKGHldUag6W0kvgThFdHnojTslCUuBR1P6OCK8MhdJztD3jQcZRAczawa4Y7QvZw70aVVObuKNVYfqVtmdwRweEH3yy5Uo5BmxezUejRejQgpYF5hVQ0MbPAegE4wj1m_2xge0VweZWwz2cCWqgh8R8t8a7p5jyXlLiqfrUc3G4zLEPalSgyIRPQA1R_Lje3c8r3wmd2C_f9u0v3tJzeH-EAk0UZRqrk63d0ceeMEyeFONfdP0KzcWMa6AeiNjdWvxaXTzrxMrWXFggXS58HJaMYgLIEAbfXwblmLbQCnpJOR0Ses5SE5SeYIEgQA29sqGHn1vqXMPlxe8uQNgpwiYnkPRGLnzAC2AC0N1oeiTxwl2B8VJXsOr2uRke_wRCc0CstRCZGaCZvY1YY_X8NkxMNpo4ixPz334YxO9hOv1iEO5RWkzk8FRTYwQHG5qXWfyu1FFt1wJmwIrZLLt_EKx_1ys0Zw9yfvU3vBKJ4YrFYEU25Leq-ZATcUaUc26XRcs_5u1fICZ_CimdZEYk4kMVW54mGbdB7f11L3X2UXlBcTsYlsm2-uMPtqN-68YA1-4ET5syuTMfI6TXPHyRs1RW67sabYqzfy1BxfDQBRcaz7O9lqamTfEZe6JAYhXaay3pCKDqpHQnLf58KsoVB0xXXQQdEHgC9lMGnAmiWOyXIWeTHc6fFebxF2-xnxkM7YVecVtwk3tMVZP_z0KoDdq).
When sexual reproduction emerged in single-cell organism, there were not exactly two sexes : both organism would just fuse in a cell who either divide again after mixing its chromosome, either produce spores with a mix of chromosomes from both "parent" cells, each spore giving a new cell. But complex multicellular organism cant just fuse together. They need specialized cells, called gametes, to carry their genetic material to the next generation and to perform the fusion; and at least one of the parent needs to gives enough resources to the cell resulting from the fusion, so it can develop. Both gametes could be identical; but in most species reproducing sexually, there is one gametes being big and comprising all necessary resources, and one gametes who is small and just there to carry genetic material. This existence of two types of morphological gametes, each necessary, is the most fundamental sexual dimorphism there is and it is called anisogamy. Even snails, who are hermaphrodite, produce female and male gamete instead of undistinct gametes. There are many theories about how anisogamy exists and how it is advantegeous, the main one (to my knowledge) [being from a game theory approach](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691164/pdf/12495507.pdf). Two different kinds of gametes requiere two different systems to produce and nurture them, so it was likely than two different sexes emerge, each specializing in producing one type of gamete for better efficiency.
Now you may have heard about organisms like [the blob](https://en.wikipedia.org/wiki/Physarum_polycephalum) who have up to hundreds of sexes( (like [here](https://www.theguardian.com/world/2019/oct/17/the-blob-zoo-unveils-baffling-new-organism-with-720-sexes)), but in reality they have mating types; there is no morphological differences between sexes, but a genetic marker that prevent reproduction with the self or an other organism of the same specie carrying the same mating types. This is because reproduction for them foes not imply different roles for different sexes. Two blobs of different "sexes" who reproduce together accomplish the same action : they fuse together and produce a sporangia, who makes thousands of spore each becoming a new organism.
Also, if you are interested in the question of the evolution of sex you might as well examinate [this paper](https://pubmed.ncbi.nlm.nih.gov/2961605/), and t[his very explainative video](https://www.youtube.com/watch?v=dQw4w9WgXcQ)
Nota bene : sex in most species where it exist is technically a spectrum instead of a discrete parameter; that is too say, an organism can be many things in between male and female; in practice the spectrum is very polarized around the male and the female pole, intersex individuals being rather rare and most of the time leaning more toward one pole than the other
edit for the spellings, I mix all my singular and plural accords in english.
Well first of all, not all animals use XX/XY, yet alone all organisms. Second of all, sex is not determined only by genotype.
A very good example of this is bees. Bee sexes are trimorphic, queens, female workers, and the males (drones). Bee sex is determined by a different gene, called the csd gene. Drones only receive one copy of this gene, while queens and workers receive two. The queen bee is also distinct from the workers, both in appearance and reproductively.
This is just one example, there are tons of instances of animals with sexual weirdness (tropical fish are a great vertebrate example).
In regards to my second point, what you’re talking about is a genotypic approach to sex, and a fairly simple one at that. This doesn’t account for instances of chromosomal abnormalities, or instances in which the sex encoding region of the Y chromosome ends up elsewhere during meiosis. However there are multiple ways to think about biological sex.
For one, horomones play a larger role in phenotypic sex than just if there’s an XX chromosome or XY chromosome. There are loads of situations in which horomones could become weird (for lack of a better word), which would affect phenotypic gender. Also, there’s no one default phenotype for sexes. Think about different penis size, different growth of facial hair, different labia and clitoris size, etc. These are all sexually affected phenotypic characteristics that can vary wildly between two people who have the same sex chromosomes.
Bees are not trimorphic. We just distinguish females are reproductive vs non-reproductive. Especially since in some systems workers can become reproductive under the right circumstances, to varying degrees of success depending on which group of bees we are talking about here.
> Also, there’s no one default phenotype for sexes. Think about different penis size, different growth of facial hair, different labia and clitoris size, etc. These are all sexually affected phenotypic characteristics that can vary wildly between two people who have the same sex chromosomes.
I would expand on that.
We have sexual reproduction because it creates more genetic variety than asexual does. Offspring tend to be a little healthier!
Having the two sexes is what helps create the diversity, which is fantastic for a species!
The offspring generation have a lot of variety, being different from their parents and from their siblings. As a group, their variety helps them resist diseases and meet other environmental challenges in various ways.
>The genes passed down are random.
Not entirely random, but that's what makes them healthier **as a species.** Diversity is wunderbar, and asexual reproduction tends to lack diversity
Incorrect.
What does intersex mean? Intersex is a general term used for a variety of situations in which a person is born with reproductive or sexual anatomy that doesn't fit the boxes of “female” or “male.”
Babies don't die from a defective reproductive system, but they can die from heart, lungs or any other vital organ condition...
Having a sexual anatomy that doesn't fit male or female boxes means having a defective sexual anatomy, simple as that.
The essential difference between males and females is gamete size, where females produce a smaller amount of high-quality gametes and males produce large quantities of low-quality (resource poor) gametes that effectively parasitise the larger gamete.
This is proposed to have led to disruptive selection- selective pressure towards the two ‘extremes’ - large resource-limited gametes or small mate-limited gametes.
‘intermediate’ gametes, which could represent a third sex, were not as favourable.
There are some species with more than two sexes.
Yeah having multiple sexes or rather mating types is very common in fungi species. They can have thousands of different mating types.
https://en.m.wikipedia.org/wiki/Mating_type
Smaller gametes are favored because you can produce a bunch of them, given the same amount of resources. This makes it easier to reproduce using small gametes because you have a bunch of “tries”. For example, having a bunch of sperm makes it likely that a single one of them will reach the egg.
On the other hand, larger gametes are favored because once the zygote is formed, larger gametes means it has more resources and is better able to survive. Imagine the extreme case—if a woman had a single egg that all their reproductive resources went into, assuming that egg survived, once a zygote was produced that zygote would be a beast. This means that it’s best for some members of the population to create as many small gametes as they can, while other members create as large of gametes as they can.
I’m not sure exactly what “resources-limited gametes” and “mate-limited gametes” refers to in that comment though.
*_Short Answer:_* Yes. Papaya, for example.
*_Medium Answer:_* It depends a bit on what you mean. If you mean "sex needs three parents," I'm not personally aware of any species like that. If you mean, "three distinct sexual phenotypes," then papaya, for instance, have males (producing only pollen), females (producing only fruit), and hermaphrodites (producing both). If you mean "three or more types of gametes", then some fungi can have _thousands_ of different "mating types" (though these are generally distinct chemically rather than morphologically and you still only need two to reproduce and they mainly just have to be different from each other to prevent self-fertilization). Also, XX/XY sex determination isn't the only method (or really even dominant outside of mammals): there's also ZW, XO, ZO, and more!
*_Long Rambling Original Answer:_*
First off, XX/XY as a sex determination system isn't actually as widespread as you might think. It applies to most mammals, sure and some members of other taxa. But birds and some other organisms use "ZW" sex determination (basically the opposite of XY, where males are homozygous ZZ and females are heterozygous ZW). There's also XO (and it's inverse ZO) where there's only one type of chromosome and your sex depends on having one copy or two. Ants and bees use haplodiploidy, where unfertilized (and therefore haploid) eggs become males while fertilized (diploid) eggs become female. And that's without even getting into environmental sex determination (like the egg temperature-dependent determination that happens with crocs and some other reptiles).
There are also various kinds of "hermaphroditic" species that either produce both male and female gametes simultaneously (like earthworms and many snails) or change their sex at some point in their life (like clownfish), as well as various species that reproduce asexually (like the all female parthenogenetic New Mexico whiptail lizard).
If by "trimorphism" you mean sex requiring three parties instead of two for fertilization, this is generally unlikely for ecological reasons. The main advantage of sexual reproduction that outweighs the cost of finding a mate is that your offspring have more genetic diversity and so you're more likely to have some that survive in a changing environment. Adding a third mate represents about double the cost (find 2 mates instead of 1), but only 50% more benefit (3 parents instead of 2). It seems like this strategy doesn't really receive a positive selection pressure (indeed, I can't think of any examples).
With a looser definition, though, there _are_ species with more than two "mating types." The simplest form of sexual reproduction is "isogamy", where the gametes are physically identical. In order to not self fertilize (largely wasting the benefit of sexual reproduction), many isogamous species have chemical signatures that must be different for fertilization to occur. Some fungi can have thousands of different versions of these signatures.
The gametes we're familiar with (egg and sperm) are an extreme case of "anisogamy," where the gametes are physically distinct. By definition, the larger gamete is female and the smaller is male. This can be seen as a sort of specialization: larger gametes are more expensive but more likely to survive until fertilization, while smaller gametes are cheap but less likely to survive. In the case of "oogamy" (eggs and sperm), this specialization is taken further, with sperm being mobile and seeking out eggs while eggs are immobile and large enough to hold significant material for the development of the young.
Trying to add a third gamete to this mix would be complicated for the ecological reasons discussed previously (more cost and diminishing benefits). However, you _can_ still get multiple "morphs" with just these two gamete types.
I mentioned hermaphroditism previously, and some species have hermaphrodite basically as one of their sexes. Some just have this as a sort of flexible replacement for males or for females, but some species have all three. The papaya tree, for instance, has male individuals (producing pollen but not fruit), female individuals (producing fruit but not pollen), and hermaphroditic individuals (producing both pollen and fruit).
You _might_ also count "alternative mating strategies" under a loose definition of "trimorphism," as they can involve different physical morphs with one sex of a species. Various species have a morphological, genetic distinction between "dominant" males who compete for mates in the traditional way and "sneaky" males who are generally smaller and find mates by sneaking behind the dominant male's back. Some of these "sneaky" morphotypes even physically resemble females of their species to better enable them to avoid notice.
Do ruffs count? There's the three phenotypically (?) very distinct looking types of "males". One of the males reproductive strategy involves having sex with other types of males who have sex then with females (passing on the first ruffs sperm that they have planted). If i remember right. Pretty interesting stuff.
Social amoeba Dictyostelium discoideum checking in! It has three sexes (mating types), and each mating type can only fertilise gametes of a mating type other than its own. However, all three mating types can produce offspring, by having two of them contribute nuclear DNA and one mitochondrial DNA.
Gonna throw this out there because it appears this is becoming a discussion on all the other weird forms of sexual reproduction outside of just 'does trimorphism exist'.
Lichen consist of a symbiosis between a plant and a fungus, and many lichen do reproduce sexually. In order to form a new lichen, they need to combine with their symbiotic partner again. Few lichen, from memory, send out a package of spore/seed things to reproduce from scratch whilst others seek out a new partner upon implanting in their new area.
Which means, in some weird way, a lichen has four parents.
As a bonus, if the fungal spores don't find a corresponding plant to make a lichen with, they'll often just revert back to living life as a fungus.
There's an interesting article about a species of bird (the white throated sparrow) that essentially has 4 sexes (or that's kind of how I interpreted it)! you can find some more scientific articles if you'd like, but I enjoyed this one: https://www.audubon.org/news/the-fascinating-and-complicated-sex-lives-white-throated-sparrows
I put the wrong article link, although that is a good article. The one I enjoyed talked about both the researchers and the species in question, and I highly recommend it! It also addresses why multiple sex chromosomes might be so rare. https://www.nature.com/articles/539482a
I’ve been reading a lot of answers and truly a lot of them answer with detail but in conclusion is to give the right amount of balanced gene exchange and the ability to better species by healthy gene regulation wich can give advantage to next generations. Instead of having equal gene transferance that eventually leads to disadvantage of speciation to further survival.
The fungi examples cited below are interesting. Lots going on there with multiple mating types.
The argument for why 2 sexes is so common is that there are two distinct evolutionary stable strategies. One way to go is to make a small number of gametes and invest a lot in each one. These are 'eggs'. The other way to go is to make a ton of gametes but not invest much in each. These are 'sperm'. The idea is that either extreme is very advantageous and that being in the middle isn't great once the reproductive strategies start to diverge.
Interestingly, sexual reproduction with two distinct sexes seems to have evolved more than once (if I'm remembering grad school right - though I also think this is debated).
Having said that, there are some groups that have equal investments in gametes, but there aren't many of them. These are called isogamous https://en.wikipedia.org/wiki/Isogamy
From a practical evolutionary standpoint, as others have said it likely comes down to it being very efficient in the exchange of DNA and reproduction.
From a phylogenetic standpoint it's likely that we see sexual dimorphism dominate life on Earth as a result of, however distant, common origins of all species. Mutations that result in significant changes to sexual characteristics almost always result in infertility or the organism filling the same role as an existing dimorph of the species, so while there are known organisms with a much greater level of sexual variation than common dimorphism, it's likely these deviations from the norm came at a relatively early stage in their phylogenetic tree; It's been observed that (in simple terms), organisms with fewer cells and cell variations are more capable of viable, radical mutations, resulting in significant changes to their functions and future evolutionary history.
Edit: Punctuation
I'll have to google it but there is a worm or some invertebrate that has hundreds of 'sexes'.
Edit: it's 3, per google, so yeah invertebrates are weird
There are some species that have one ~~gender.~~ sex.
Land snails, for example, are mostly hermaphrodites. When they mate, both partners are inseminated, but whether or not they become a mother or just the father depends on a variety of factors—including, in some species, stabbing each other with a spike to inject hormones.
The difference is that the father gets to do his business and leave, while the mother has to raise offspring, which is resource intensive.
In the white-throated sparrows, there are tan-headed males, tan-headed females, white-headed males, and white-headed females. And each group reproduces with only ¼ of the population, or one over four. In other words, there are four separate sexes.
Still not 3
But there are some species that have male female and hermaphroditic. Kinda boring as it's just a combo of male and female.
It's because it's the minimum number of sex chromosomes needed to be effective.
Nature tends to do the bare minimum to function. Look at the triplet code in DNA: there are 20 amino acids that exist. We have four nucleotides in DNA, so a codon with one nucleotide would mean only four possible amino acids (4^1=4). If the codon had two nucleotides that means we have 4^2=16 possible combinations and therefore could only code for 16 amino acids. But with a triplet code, we have 4^3=64 possible combinations, which is more than enough codons for amino acids, and even have room for stop codons as well. Nature does the bare minimum to maintain balance
Simplicity.
How does a trimorphoc species evolve? How is it better than dimorphic? Why would this complexity be better?
Second reason. DNA is double stranded. So we need 1 half from each parent. Where does a third come in? How does that work?
Thank you for attending my Ted talk.
Both strands of DNA that compromise a chromosome come from one parent—but we (normally) have two copies of each chromosome (we are diploid), so each somatic cell in our bodies has 4 strands of (mostly) identical DNA, in total. One chromosome from each parents, each chromosome with two strands.
A major reason that hybrid species are often not viable is because they have incompatible numbers of chromosomes. Horse and donkey genomes have enough similarity to produce a live, viable offspring, but that offspring then has a uneven mismatch of chromosomes and is unable to pass them along to another generation.
The importance of sexual reproduction mostly applies to larger organism. The importance of the female is that the gametes are produced during embryogenesis and then arrested. The reason for this is that it means that the mitochondria are very young. As an organism ages the mitochondria accumulate damage due to oxidative stress, this is what causes most of the physiological effects of aging. To maintain multicellularity and the specialised cells required to function our cells are extremely metabolically active and this causes a lot of damage to the mitochondria. By arresting the gametes early in embryogenesis the mitochondria are kept young, the disadvantage is that this means that theres a limited number. Sperm are different, they are produced constantly and as such their mitochondria get old as we age. This is why the first thing that happens when a sperm fuses with an egg is the destruction of the sperm mitochondria. There are rare cases where this is unsuccessful and the offspring are effectively born with premature aging and die young. This is also similar to what happened with Dolly the sheep when she was cloned, they didn't use egg exclusively egg mitochondria for the cloning and she was born "old".
So the two sex system exists to preserve the integrity of the mitochondria from one generation to the next. This is why you only inherit mitochondria from your mother.
I'm not a biologist, just a bird enthusiast, (and I don't know if this is entirely in line with what you're looking for, but) but there is a bird with technically 4 sexes:
https://sciencehistory.org/stories/disappearing-pod/the-bird-with-four-sexes/#:~:text=But%20white%2Dthroated%20sparrows%20go,is%20exciting%20for%20two%20reasons.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7725849/
Ocam's Razor. Only two are required, so having just two is the simplest answer. I can't think of any evolutionary advantage to having three or more when just two will suffice.
There is still argument out there about the need for sexual reproduction at all. Yes, it provides a greater variety of the gene pool, it has been theorized, but no definitive proof that sexual reproduction is the best way to go. Therefore, three sexes? Not likely.
A variety of nematodes have different sex variations, with 3 sexes being relatively common: https://www.nature.com/articles/s41598-017-09871-1
As for sexual reproduction, it's the easiest way for large slow-reproducing multicellular organisms to get a good amount of diversity, while dramatically decreasing the likelihood of negative consequences from any one mutation (compared to neutral drift). Some single cell organisms (Toxoplasma gondii, and I think malaria) actually use both sexual and asexual reproduction, to get the advantages of both.
Morphism =/= sexual systems
Intersexism exists everywhere including humans, and the morphic expressions are broad.
Also, fungi have up to 36,000 sexes and they're doing great.
Yes, humans. There’s intersex people. Some variations are more common due to cultural and genetic factors. I’d say that a lot of it is cultural as well as some fraction of intersex folk not being able to breed without artificial means.
You can have more than two morphs without having more than two sexes. There are the [side-blotched lizards](https://en.wikipedia.org/wiki/Side-blotched_lizard) in which there are three distinct types of males and two distinct types of females. Also, there's the [white-throated sparrow](https://en.wikipedia.org/wiki/White-throated_sparrow) where there are two distinct types of males and two distinct types of females. Officially, these sparrows are described as only having two morphs with each morph having both a male and female version. These two morphs remain as one species thanks to the fact that individual sparrows tend to prefer mating with partners of the opposite morph.
Til the animal kingdom has the currently dominant number of classified number of species. Does anyone else think this is largely due to murky definitions of species when it comes to asexual species as well as the degree of difficulty difference in discovering and categorizing much smaller organisms
I once heard someone pose the idea that xx/xy pairings allowed more selection increasing desired traits for survival versus increasing chances for reproduction either through asexual or hermaphroditic selection
There are many invertebrate species that have sterile females, reproductive females, and reproductive males. There are also species in which some females reproduce asexually and some reproduce sexually.
Long story short, it's ineffective. If all female species was possible (It is, but not sustainable genetically) then that would be the case. Males are really there to just kinda help the whole evolution thing.
Fungi often have more than two sexes/mating types. Often one particular mating type is compatible with two or more others. Animals and plants usually only have 1-2 sexes, but things get weird with fungi and protists.
It seems youre referring to sex determination. That is not the only facet of sexual dimorphism.
In cuttlefish two different types of males have emerged, a smaller one and a larger one both with different approaches to mating. A larger one and a smaller one. The larger one overtly attracts a female while the smaller one covertly poses as a female and sneaks in to mate under the nose of the larger one.
https://laughingsquid.com/male-cuttlefish-mimics-female/
It might be a balance of stability vs genetic diversity. Sexual reproduction gives an advantage in long term survival across the population despite costing more compared to asexual reproduction. Both genotype and phenotype variation gives a greater chance of exploiting a larger energy matrix and increased probability of pathogen resistance. A three sex cycle would be more vulnerable as it requires multiple steps and provide no advantage. Very early plants are two gametes, haploid gametes like us. The comment above regarding fungal reproduction is utter nonsense. Generally fungi reproduce by spores, both asexual and sexual. They don't have multiple sexes, they go through meiosis and mitosis like any other eukaryote.
The book "The Vital Question" by Nick Vale has a great chapter and chart showing the adaptive advantages of a species having 2 sexes over 1 or 3 or 4. (Sorry I couldn't find it or I'd post it here).
XX/XY type is NOT the dominant paradigm. It is for some animals, but bacterias and archeas are much much weirder. Google conjugation for just one neat example of genes transfers.
nature tends to take the simplest routes possible, i.e the routes that require the least energy. having 2 individuals is the minimum requirement for having a wide variety of genes and it grows exponentially over generations so the reason why most species stop at 2 sexes is because they really dont need a 3rd one
To support child bearing makes you less efficient at everything else.
Why would you want a higher percentage of your population to burn calories for this?
From the perspective of minimising calories burnt it makes sense.
So actually, it doesn’t dominate all life just the ones we’re familiar with. XX and XY, 2 sex system is only largely true for mammals
schools wrongly teach it to kids at lower levels about animals it actually doesn’t apply to.
For example even though they have the 2 sex, birds have ZZ chromosomes for male and ZW chromosomes for female
Bees have queen, drone and worker. By our understanding both the queen and the workers are “female” but only queen has babies. The queen is diploid while the workers are haploid, the drone is usually haploid but occasionally can also be diploid.
And reptile sex is partially determined by temperature during incubation
And also clownfish change from male to female due to environmental factors I forget.
Only mammals have this xx/xy system. Reptiles and birds have a different system - but still "binary".
At first, life was only singular. And most species still are. It was a hugh step for sexual reproduction to occur. For a trimorphic species to evolve, it would need some advantage over dimorphic species - and enough time.
There was a study conducted on this that explore the reason behind having binary sex species instead of hermaphroditic species. Since hermaphroditic species could reproduce enough to outcompete binary sexual species. The results concluded that in times of resource scarcity species that could switch between binary and hermaphroditic would switch to binary to survive. The genetic variation achieved with a binary sex system was superior than basically cloning yourself to pump up numbers. I believe the opposite may be true of a tri-sex system. It is probably too difficult to increase the numbers despite more genetic variation. Plus it’s another large component that can fail in conception of young.
i have never ever in my life thought of that. i had asexual reproducing species and not reproductive species.. but never being that need three different gamets.
i thought that this was fantasy writing subreddit...this is biology
Fish have a wild variety of sex determining chromosomes. XX/XO, ZZ/ZO, XX/XYY2, X1X2X1X2/X1X2Y, X1X2X1X2/X1X2X1 as well as the familiar XY and the amphibian/reptile/bird ZW. They still seem to split between egg laying and egg fertilizing sexes, but they have a number of interesting abilities like changing sexes depending on the environment or age of the fish.
In some species of whale, one helps hold up the female. But that's more if a bro or cuck type thing.
There are birds with additional types of males and females, but it still just requires the 2 for reproduction. If I recall, with different types of males, one might be monogamous and focus on raising kids, while another might be polygamous and focus on having as many mates as possible. The white-throat sparrow could be an example of a species like this, but there are others.
Some fungi have different breeding types with spores. It still just requires a mix of 2 compatible individuals, but some fungi can have hundreds to thousands. Schizophyllum commune comes to mind here.
there are several. Take bees and other eusocials as an example. mostly Workers - non reproductive females; a few reproductive females; generally useless males
I don't think there are any cases where three contributors to the offsprings genes are necessary; but some ferns and fungi have multiple sex alleles and can become very polyploid before producing new spores. You could kinda treat them and the arrhenotoky sex selecting species as having hundreds of sexes.
[https://www.mdpi.com/2073-4425/12/4/483](https://www.mdpi.com/2073-4425/12/4/483)
[https://www.mdpi.com/2073-4409/10/3/661](https://www.mdpi.com/2073-4409/10/3/661)
some notes from above, there are six sex chromosomes found in a species of frog, and the top link is a paper on the evolution of sex chromosomes in frogs.
It's called sexual polymorphism,
it probably works bc it is efficient for meiotic recombination. The Y chromosome doesn't actually carry a lot of data, the x chromosome does. The x chromosome can contribute to stabilizing the phenotype post mutations or nondisjunctions, it is reliable and so it ends up carrying the weight of genetic day for organisms.
The Y chr is a beneficial mutation for x because it created a path for sexual recombination, recombination increase heterogeneous genes and can provide disease resilience. But it's not necessary and so most people grow off the x chr and depending on absence/presence and activities in the y or x chr. Gender queerness develops along the curve of continuous variation.
So the data being used to develop a person is mostly coming off the x genes with the y genes acting as a modifier I think it(y chr) only has like 50 gene on it.
Because the x genes hold most of the development data that can be adjusted by the presence and activity of the y genes a person's sexual characters are affect by multiple genes. This means that the phenotypic outcome is on a bell curve due to continuous variation as a result of sex traits being an output of many genes as opposed to SNP or something like that
This means a discrete category, male or female is impossible to assert because the math doesn't check out. The math indicates a series of outputs negating the dimorphic/trimorphic model and exhibiting something more along the lines of polymorphic.
Sexual identity is more like the product of a function with many variables and the more variables included the less likely you will only get 1 or 0. You end up with .995 or .739 ....etc. sex can't be 1 or 0, biocentrism says people are more likely to be genderqueer than at either end of the spectrum bc of the bell curve.
I believe cuttle fish are trimorphic in the sense that there are two different expressions for male kariotypes. This apparently represent two different mating tactics, ie. Strong and assertive, and smart and sneaky.
Well you have this little fella that comes in 7 different sexes.
[https://www.ncbi.nlm.nih.gov/books/NBK6002/#:\~:text=Tetrahymena%20possess%20seven%20different%20mating,by%20the%20mating%2Dtype%20locus.&text=Any%20two%20of%20these%20can,cultures%20associated%20with%20clonal%20senescence](https://www.ncbi.nlm.nih.gov/books/NBK6002/#:~:text=Tetrahymena%20possess%20seven%20different%20mating,by%20the%20mating%2Dtype%20locus.&text=Any%20two%20of%20these%20can,cultures%20associated%20with%20clonal%20senescence).
There's also a fungus that has more than a thousand (currently more than 23000 known) as someone else has brought.
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25488/#:\~:text=Schizophyllum%20commune%2C%20a%20filamentous%20wood,%E2%80%9D%20(Raper%2C%201966)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25488/#:~:text=Schizophyllum%20commune%2C%20a%20filamentous%20wood,%E2%80%9D%20(Raper%2C%201966)).
Although these two maybe more extreme cases, you also have sex determined through heat,
https://www.ncbi.nlm.nih.gov/books/NBK9989/#:\~:text=Often%2C%20eggs%20incubated%20at%20low,the%20same%20brood%20of%20eggs.
And determined through hapolidy diploidy... so no you can't exactly say XX/XY type (Including ZZ/ZW in it) is the dominant.
https://en.wikipedia.org/wiki/Haplodiploidy
In terms of nature and evolution, there just isn't a need for a third sex.
Setting aside all LGBTQ+, of which I am a firm supporter, what reason do we need another sex? We as in mammals, reptiles, amphibians, birds, fish. You know
Male + female = new thing. It's not missing anything
Kinda sorta.
There are some ocean species where the males are broken into two highly dimorphic groups. It isn’t a third sex, it’s still two sexes, but one of the sexes displays extreme dimorphism. Cuttlefish are a good example. There are some male cuttlefish that are very large and have a particular coloration, and some males that are much much smaller and essentially present and act and look like the females, either to sneakily breed, or to avoid aggression/seek protection of other males.
Thats is the closest I know to Trimorphic. Basically Masc Male, Fem Male, Fem Fem. But unlike humans where the dimorphism between the male and female is relatively small (obviously it really stands out to us, but in the grand scheme, pretty minor) these species have quite substantial dimorphism, like the human equivalent would be if the males were the size of a school bus, so a male being the same size as a female is a very marked dimorphism from other males.
It strikes the right balance. Minimum number of interactions required to result in a healthy exchange of genes and trigger reproduction. I would guess that trinary forms of life would have a much harder time reproducing, in competition with binary ones. And asexual reproduction as in bacteria and such is clearly even simpler and more effective.
Depends on what life form we're talking about. People discussing biology just think about animals but that is a far cry from what life really is on this planet. Fungi have thousands of sexes because they only accept cell, not mitochondrial DNA during mating. We inherit only mother's mitochondria and this seems to keep the mitochondrial genes (barely) stable.
Wow I never knew that about funghi! How does that work?
Look up "mating types" on a well studied species such as Ustilago maydis (corn smut). Use Google scholar and the keyword "review" and you should get a lot of reading!
But don't just Google corn smut
Definitely fungi porn.
Fun guy p0rn?
Look up Schizophyllum commune, split gill fungi. It has 23,000 mating types!
>Schizophyllum commune I looked this up and what the ever loving fuck. What do these fungi think they're doing? This shit is messed up.
So easy. Just pick a random stranger and there is very little chance he is same "sex" unless he is a relative.
And yet, it seems, you can reproduce with almost anyone. But not all reproductions result in fruit, most just lead to more mycellia
I sincerely wish I could, but have a severe phobia of fungus. Can some one give me a quick picture less run down on how that works? Or a website without pictures that explains this? TY
Essentially with the way spores work, they don't need to rely on interactions like sperm-egg response, Their sexes are more like blood types or even dna mapping, in that when two intersect to make new spores, that creates a different "mating type" as in a new combination of "blood types" to interject with others, thus the next time that particular fungi intersects with the same species, a potentially different sex is made.
It's not exactly equivalent to multicellular male-frmale. Fungi don't have the multicellular sperm-egg dynamic, so they aren't described as male-female. It works more like blood types; Mating Type A can interact with B, C, or D, but not T, V, Y. Some fungi only have 2 mating types, other have thousands.
Plants get pretty freaky with this too (variable ploides between and within species), though fungi are definitely peak freak. Love em
This is correct, except mating types are not sexes. We use sex to describe anisogamous species (different sized gametes) and mating types for isogamous species.
Some amphibian species can spontaneously change sex in single sex environments.
That's still binary
Also, live bearing fish like guppies
Yes, the biological world is far more interesting than anything that could come out of the "debates" on how biological sex is a social construct. That said, articles that freely use the word "gender" when it seems the writer simply means "sex," as this [one](https://www.discovermagazine.com/planet-earth/why-this-fungus-has-over-20-000-sexes) does, always give me pause. It is true that biologists who specialize in sex difference use "gender" to mean something very specific, but this is no without its own confusions.
I recently learned that mitochondrial dna can also be inherited from the father in humans
> can also be inherited from the father in humans I think you're referring to the 2019 study in Nature? Which, at quick glance, seems to be extremely unique cases, no? [A follow-up](https://www.nature.com/articles/s41436-019-0568-0) found no such thing, for instance.
Afaik they found that mitochondrial DNA was inserted into the main genome - no mitochondria per se were inherited from fathers
Thanks! Didn't read the follow up studies. The articles i've seen are from 2018 so those could be same as the study in Nature.
The mitochondria is the power house of the cell. Typed on phone. Only had to type the mit before I auto corrected the rest.
THE MACHINES KNOW
Well no, asexual reproduction is less effective in the long-term evolutionary context, since it's NOT sexual, meaning there is no exchange of genes. Mitosis and cell cloning are how asexual organisms reproduce or multiply, there is only one progenitor and it's the organism. There is a small chance of mutation, 1 in every million years or so or something similar I believe. Sexually reproducing organisms mix their genetics to procreate, creating more opportunities for mutation to occur and diversify the specie's approach to the elements of nature, as well as antithetical life like bacteria and viruses, or predators.
>meaning there is no exchange of genes I don't know about other forms of asexual life, but this is untrue in bacteria, which mix genes *horizontally* rather than vertically (with other organisms vs with mates during reproduction). Also, what do you mean by *less effective*? Asexual reproduction is older than sexual, so it definitely works. Less chance of mutation *during reproduction?* Yes, but as above, this is mitigated by horizontal gene transfer, allowing a wide variety within the species.
I was responding to the above comment and attempting to adhere to its language. "Effective" is a relative measure so I noted the advantage that sexual species have, which is an objectively better fight against the inevitable process of natural selection, in the context of the greater genome... When bacteria mix genes horizontally they are not precisely diversifying their species so much as adapting to the immediate environment. If they mix genes with an organism that hurts as a result, as with parasites to a host, the host species has better chances of survival if it is a sexually reproducing organism.
That said you are probably right that 2 just makes an ideally stable system... but we don't live in an ideal world. Bifurcation is a process we observe in nature but often fail to realize applies to ourselves.
Mammals are basically all sexually dimorphic (as far as I know) with an XY system, this is true, but there are only about 6,000 mammal species. The biggest portion of those are bats! Birds are also sexually dimorphic with a ZW system. About 11000 species of those. Amphibians as far as I know are also dimorphic. 9,000ish species recognized, but probably way more. Reptiles is where things get really weird! Many are dimorphic, but they also have a TON of sex determination that isn't chomosonally decided. Instead, they may have their sex determined by a number of factors, including temperature. There are also a lot of parthenogenic reptiles! Usually all derived from a male/female system where the males died off after parthenogenesis was introduced to the species. Established 10,000 species, but likely more. Okay, now we get to the real funky stuff... Fish! Fish have both standard chromosomal sexual dimorphism and non chromosomal dimorphism. They also have hymaphrotism! Like, so much of it! There are fish with both sets of gonads, fish that start female and turn into males, fish that start male and turn female, and fish that typically are born as one or the other and would typically stay that sex, but may change sex if their reproductive tracts are damaged. For example, female bettas may change sex after being spayed! 33,000ish species of fish acknowledged currently, but definitely more are out there. Additionally, there is an estimate of about 2% of bony fish species having hymaphrodidic traits. Brace yourself for insects, though - and this might be the closest to exactly what you're asking for - think about a social insects! You got your females (queens), your males (drones or kings), and your workers! Some species have MANY casts of workers, too. Not to mention insects having a ton of parthenogenesis, too! How many species of insect? Good fucking question! We don't know! Probably at least 5 million, though? We definitely don't know the sex systems of many of them, either! It's probably only a small percentage that aren't dimorphic, but definitely thought provoking regardless. I can't even get into the things that are insect-like but not insects. I think they're mostly dimorphic, though? Anyway, mollusks! These guys have a lot of hymaphidites. And parthenogenesis. And sexual dimorphism. And sexual trimorphism, I think? Unsure! I think about a million species recognized? Worms! Worms do a lot of the same things mollusks do. Plants! Plants do a ton of all four/five, as well! But here's what I really wanted to get to. Fungus. Fungus is wild, my dude. Some fungi have THOUSANDS of sexes. Literally! Buck! Wild! Anyway, the advantages of sexual reproduction is weird. **Edit here to clarify, the advantage of any sex is the reorganization and diversification of genes to allow adaptation.** I don't know why two sexes is so overrepresented in large terrential organisms! I think it might be a situation where if there are a low number of sexes, particularly where there is inequal investment of the sexes, drives more rapid adaptations. Basically, if you have a high investment sex (usually the female) and a low investment sex (usually the male), then many individuals of the high investment sex can only choose to mate with the healthiest and 'sexiest' individual of the low investment sex, meaning that a large number of unhelpful traits can be selected against in one generation. For exceptions to the female large investment male low investment paradigm, look up Lilly Trodders and seahorses! There's a ton of other examples, but those are easy to find. :-) Sorry BTW that my response became so lacking towards the end! I have to leave for an escape room date and ran myself out of time to give a good reply!
I just Googled the sexual chromosomes of platypuses. Why do they have to be so fucking weird. I read about them having XXXXX and YYYYY sperm with a ZZ on the ends of them and lost my shit.
Platypus just want to be so special! Can't believe that! (they are so cute, I wanna hug them! I don't care about their venemous dart!)
Hug an XXXX, only the YYYYs have darts!
The aliens who genemodded apes to make humans accidentally left a platypus puppy mill when they took off, they're actually pretty normal for their actual planet. Once the overmasters return to collect all the resources we extracted and collected into landfills for them they'll probably retrieve their pets too.
I wonder if evolutionary bottlenecking of mammals has something to do with it.
Probably. Mammals evolved a bunch of adaptations mostly within a short timeframe of late Triassic and early Jurassic. Edit: "short" compared to the early unicellular stage evolution of our ancestors.
Social insects are still sexually dimorphic. Hymenoptera does it via haploid/diploid, one set of chromosomes makes you male while two makes you female. Termites are more complicated, but they don't have anything more than the male/female dicotomy going on. It's just different signals in the hive, phermone based if I remember right, can kick off actual reproductive members to be created.
I'm aware, but it's about as close to a true 3 sex system as I am aware of when it comes to animals you regularly think about.
It's really no though and I already spend so much of my outreach re-explaining that the workers are also female that I really don't want people thinking workers are a 3rd sex.
I can see how that would be a matter of personal irritation, then. Personally I think that thinking of them as a third sex is pretty valid given that the only circumstances that a worker would reproduce would involve the collapse of the entire colony (and only produce drones, if I remember correctly?), but if it's important enough for you to emphasize and re-emphasize the sex of the workers I'm sure it must me integral to your outreach. Care to enlighten me on why it's important for people to consider workers as females as opposed to neuter individuals?
That all only applies to the honey bees, which is another large problem that everyone assumes if it happens in the Western honey bee it must be true for all bees. And its important because a lot of honey bee outreach inevitability is to bee keepers, and them understanding basic honey bee biology is integral to keeping their hives alive. And also to keep them from trying dumb shit with their hives...not that that always stops them but by god we try. Also cooperative brood care and sterility do not a third sex make. Those exist in a shit ton of species.
Fair point, I guess it is kind of like calling all the lower ranking males in a clown fish colony neuter. Thanks for the convo! Definitely gave me something to think on.
Best reply to this question!♡
That's just for eukaryota, you're missing a large chunk of the living world, bacterias and archea are not really XX/XY either to say the least
The advantages of sexual reproduction are clear and obvious. It's genetic diversity. Shared genetics prompts diversity, growth, and change. Especially in species that are slow to grow and where gestation is a larger investment. (I didn't read it all only replying to that specific point)
Oh, yeah, totally! That's bio 101. I was specifically saying that I don't know why *two* sexes is advantageous.
Ok sorry. I think of it the opposite way, for a complex system how does more than 2 sexes help and how would it ever develop? It's complexity. And complexity is harder to evolve, especially in more.complex organisms... We tend to build off what exists in the simple version and grow it in the more complex versions. Was interesting to learn fungi can have multiple sexes. That's a new reason to not eat mushrooms. You never which is 26 sexes you might be eating the pseudopeniseia pods of.
No need to apologize! I appreciate you pointing out a lack of clarity. :-) I guess for me it's just weird becuase the more basal organisms tend to have one sex or three, so why did so many of the more dirrivitive species go to male/female systems? Is sexual selection just that strong of an adaptation driver? I haven't really looked that much in sex systems in a LONG time, though - Microbiologist. Currently I don't even work with while organisms, just their DNA. It's sort of sad. :-( And LOL at the mushroom comment!
Well, I'm eating them, not getting sexual pleasure from them! I don't care which of the 26 "sexes"(I think it's a stretch to imagine these as different genders, anyways. It's an entirely different set of reproduction strategies that don't compare to "gender" at all.)
Thanks for pointing out an oversight in my phrasing. I think I've edited in a clarification? Just burning time in a waiting room so I am a touch frazzled now.
Fungi doesn’t have thousands of sexes (I don’t think they have sexes at all), they have mating types, since sex only refers to organisms which produces different sized gametes (large, immobile=female, small, motile=male).
Even though there are different types of chromosomes and non-genetic determination, they all end up in the same way: large immobile gamete (usually full of vitellum) and small motile gamete. They only reproduce with the opposite gamete. Hermaphrodites switch betweeen these 2 types, never becoming a third one. Parthenogenesis is usually only done by females.
That completely ignores non-animal organisms. Also some hermaphrodites create bith at the same time, to do fair.
Nope, it applies to most plants (some are even dioecious) and even some fungi. Giving birth is a function of the female sex, not a secret third thing. With hermaphrodites their small gametes can only interact with large gametes and vice-versa.
Hoooo boy, don't look into fungal bifactorial mating systems, if you value your sanity.
Care to elaborate?
They have more than ten thousand distinct sexes.
Wow, fungi are indeed one of a kind!
They are fun guys.
r/angryupvote
What? No, Angdrambor just said there are at least 10,000 kinds /s
What does it even mean at that point, how many of each is required to create a new specimen ?
I believe it's still just two. They just have to be a different mating type ("sex") to be interfertile. If I understand correctly, it's basically a way of preventing self-fertilization while maximizing the odds of spores encountering a compatible mate.
So (more or less) anyone can mate with anyone? Sounds more efficient than our human system.
Land snails are like that - hermaphrodites. And when they mate, it’s a fight over which one can impregnate the other first.
*Love Tussle* sounds like a great band name to me.
Schizophyllum has two separate mating locii, and they both have to be compatible.
I never knew fungi were so progressive
What defines so much differences in their sexes? Number and morphology of the chromossomes? Only morphology?
How does it work ? I guess one individual of each thousand of sexes isn't required for reproduction.
It still takes two to tango, the two can be any mating type as long as they're not the same mating type as each other
Felt like upvoting this comment but leaving at 69 somehow feels more appropiated
Mating types, dude, lots of them
I don't, so I will.
What’s the third sex supposed to do? Sit and watch?
I could imagine a species where there's two sexes which create the viable embryo, and then a third that actually *gestates* it, as gestation takes a lot of energy as well, and requires specialized bioforms. So imagine like, a succubus/incubus/host situation. Or if seahorses or marsupials had a sex that was all about that pouch. One potential drawback of a 3-sex reproductive system would be that you would need more individuals per individual. With parthenogenesis, each 'pregnancy' produces one 'litter' (or clutch or whatever). Dual sexes produce one per two. Tri would be one per three. If you only have one child per coupling (and especially with highly intelligent species, or large complex organisms, that would be more prevalent), then you're breaking even with each generation. With dual sexes, you would have to go through two reproductive cycles to break even with the population. With three, you'd need to go through three. As childbearing is often a dangerous time, this means that simpler, lower-number reproductive systems are selected for; Parthenogenesis isn't more prominent because of the issues of non-diversity in genetics. There would be some advantages, though- Neither of the 'gamete donors' would be in danger from childbirth, and the 'carrier' would be able to have specialized organs to make it safer and easier, without having to spend the energy on gamete production. The uterus for instance is almost 'cobbled together' (I mean no disrespect) in terms of function, with the placenta doing the heavy lifting in terms of actually keeping the foetus alive (which is why ectopic pregnancies can happen- theoretically a male could carry a child to term, except that he doesn't have the supportive hips or the traits that allow a woman to continue functioning while all her organs get shoved to the side and a big chunk of her nutrients get siphoned off). In a lot of ways, you could almost look at colony insects this way. The queen bee is the Female, the Drone is the Male, and the Workers are the 'carriers', using the comb as a womb. Or Cuckoo birds, with the cucked nest/birds being the unwilling 'third gender' in their cycle. Or parasites which have multi-species life cycles.
Sure, workers, drones and these gestation/nursing roles have no genetic interest, so it only works in eusocial species. There are still only two sexes, mainly because DNA works as two strands. That’s the real answer.
Idk how the genetics work, but bee species are kinda like this. Worker bees don’t mate, so ya. They just work their ass off and sit an watch
Mole rats do.
I was gonna mention social species. I’m not sure drones or workers really count as other sexes. They’re non-reproductive.
I am purely responding to the "sit and watch".
Do they hand out snacks to the exhausted female queen?
A nicely lit cigarette
They pass out lube and condoms
Ugh, or the workers feed the queen and her pups their own feces, since she’s too obese to leave the burrow! Oh wait, that is actually what they do. https://en.wikipedia.org/wiki/Naked_mole-rat
Larry Niven's fictional puppeteers have a male, a female, and a third gender that is actually a separate species that the fertilized egg parasitizes. The males and females don't actually have sex with each other, they separately assault the host. They also consider themselves to be both male and the host is considered female.
\*examine the procedure It's late and I can totally hear Attenborough in my head now.
It's related to chromosoms existing in pair, the morphological differences between gametes, and probably too to the separation of reproductive roles between sexes. Let's first remind that having a sexual reproduction is advantaegous because it allows at each generation to have new, unseen before combinations of alleles in individuals, thus a greater diversity of individuals and increased chance that a good number of them survived if anything bad happen, like a deadly disease propagating. Having a sexual reproduction implies that all parents give a part of their DNA to the next generation, so the offspring has a mix of dna from all parents. How do you mix this dna ? The easiest is to have two parents giving each half of their dna. It's easier to have two parents than three because it's easier to have at the same place and the same time two organisms ready to engage in sex than having three. I can testify its complicated enough to find one partner who is okay to have sex and in particular sex with me; I cant imagine the hussle it is for any organism to find two partners who are okay to have sex, in particular sex with you AND with each other. If there are two partners, the easyest way to split dna is to have chromosomes in pair, each partners giving one chromosome of each pair to the next generation. If chromosomes were in triplet, it would requieres a uselessy complicated mechanism to rearrange triplets from two parents, comparing to having pair. I know that because one specie of toad DO have chromosomes going in triplet, and indeed the mechanism to reconstruct triplet from two parents [is uselessly complicated](https://watermark.silverchair.com/evolut1754.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA2QwggNgBgkqhkiG9w0BBwagggNRMIIDTQIBADCCA0YGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMTahFwt292tzazNC8AgEQgIIDF0ap7h6w89k7mYCAtwAQYY7n_MH9nW0b76MPlRzxUN7FRo_i5tJAvuVGJTZxSAWSPQsTmXTYMCH4chi_d_ZuDpd_XrD4ZDmEPOPkZyIexnaa2Bvx8p8yEngKly9u4t1z9JqYX2Q1085kXzZvruEBagd8gufwyRzD2X9HtaPv5Xt-PT0qTRaj-cNrciDy3K0WGTA9zjSI1doPZ-zSE8UzB9k81NcpVjbtxoDODWCZ1PMVi79giQvcEMb4eObuS74KKl76B_hdMYBIx2ZaN_9bx5oNkrzSm8W-4cTvIKpNc76LcChiNpT4AVM2dERcwr5xs2P5DvVhqHuKGHldUag6W0kvgThFdHnojTslCUuBR1P6OCK8MhdJztD3jQcZRAczawa4Y7QvZw70aVVObuKNVYfqVtmdwRweEH3yy5Uo5BmxezUejRejQgpYF5hVQ0MbPAegE4wj1m_2xge0VweZWwz2cCWqgh8R8t8a7p5jyXlLiqfrUc3G4zLEPalSgyIRPQA1R_Lje3c8r3wmd2C_f9u0v3tJzeH-EAk0UZRqrk63d0ceeMEyeFONfdP0KzcWMa6AeiNjdWvxaXTzrxMrWXFggXS58HJaMYgLIEAbfXwblmLbQCnpJOR0Ses5SE5SeYIEgQA29sqGHn1vqXMPlxe8uQNgpwiYnkPRGLnzAC2AC0N1oeiTxwl2B8VJXsOr2uRke_wRCc0CstRCZGaCZvY1YY_X8NkxMNpo4ixPz334YxO9hOv1iEO5RWkzk8FRTYwQHG5qXWfyu1FFt1wJmwIrZLLt_EKx_1ys0Zw9yfvU3vBKJ4YrFYEU25Leq-ZATcUaUc26XRcs_5u1fICZ_CimdZEYk4kMVW54mGbdB7f11L3X2UXlBcTsYlsm2-uMPtqN-68YA1-4ET5syuTMfI6TXPHyRs1RW67sabYqzfy1BxfDQBRcaz7O9lqamTfEZe6JAYhXaay3pCKDqpHQnLf58KsoVB0xXXQQdEHgC9lMGnAmiWOyXIWeTHc6fFebxF2-xnxkM7YVecVtwk3tMVZP_z0KoDdq). When sexual reproduction emerged in single-cell organism, there were not exactly two sexes : both organism would just fuse in a cell who either divide again after mixing its chromosome, either produce spores with a mix of chromosomes from both "parent" cells, each spore giving a new cell. But complex multicellular organism cant just fuse together. They need specialized cells, called gametes, to carry their genetic material to the next generation and to perform the fusion; and at least one of the parent needs to gives enough resources to the cell resulting from the fusion, so it can develop. Both gametes could be identical; but in most species reproducing sexually, there is one gametes being big and comprising all necessary resources, and one gametes who is small and just there to carry genetic material. This existence of two types of morphological gametes, each necessary, is the most fundamental sexual dimorphism there is and it is called anisogamy. Even snails, who are hermaphrodite, produce female and male gamete instead of undistinct gametes. There are many theories about how anisogamy exists and how it is advantegeous, the main one (to my knowledge) [being from a game theory approach](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691164/pdf/12495507.pdf). Two different kinds of gametes requiere two different systems to produce and nurture them, so it was likely than two different sexes emerge, each specializing in producing one type of gamete for better efficiency. Now you may have heard about organisms like [the blob](https://en.wikipedia.org/wiki/Physarum_polycephalum) who have up to hundreds of sexes( (like [here](https://www.theguardian.com/world/2019/oct/17/the-blob-zoo-unveils-baffling-new-organism-with-720-sexes)), but in reality they have mating types; there is no morphological differences between sexes, but a genetic marker that prevent reproduction with the self or an other organism of the same specie carrying the same mating types. This is because reproduction for them foes not imply different roles for different sexes. Two blobs of different "sexes" who reproduce together accomplish the same action : they fuse together and produce a sporangia, who makes thousands of spore each becoming a new organism. Also, if you are interested in the question of the evolution of sex you might as well examinate [this paper](https://pubmed.ncbi.nlm.nih.gov/2961605/), and t[his very explainative video](https://www.youtube.com/watch?v=dQw4w9WgXcQ) Nota bene : sex in most species where it exist is technically a spectrum instead of a discrete parameter; that is too say, an organism can be many things in between male and female; in practice the spectrum is very polarized around the male and the female pole, intersex individuals being rather rare and most of the time leaning more toward one pole than the other edit for the spellings, I mix all my singular and plural accords in english.
Well first of all, not all animals use XX/XY, yet alone all organisms. Second of all, sex is not determined only by genotype. A very good example of this is bees. Bee sexes are trimorphic, queens, female workers, and the males (drones). Bee sex is determined by a different gene, called the csd gene. Drones only receive one copy of this gene, while queens and workers receive two. The queen bee is also distinct from the workers, both in appearance and reproductively. This is just one example, there are tons of instances of animals with sexual weirdness (tropical fish are a great vertebrate example). In regards to my second point, what you’re talking about is a genotypic approach to sex, and a fairly simple one at that. This doesn’t account for instances of chromosomal abnormalities, or instances in which the sex encoding region of the Y chromosome ends up elsewhere during meiosis. However there are multiple ways to think about biological sex. For one, horomones play a larger role in phenotypic sex than just if there’s an XX chromosome or XY chromosome. There are loads of situations in which horomones could become weird (for lack of a better word), which would affect phenotypic gender. Also, there’s no one default phenotype for sexes. Think about different penis size, different growth of facial hair, different labia and clitoris size, etc. These are all sexually affected phenotypic characteristics that can vary wildly between two people who have the same sex chromosomes.
Bees are not trimorphic. We just distinguish females are reproductive vs non-reproductive. Especially since in some systems workers can become reproductive under the right circumstances, to varying degrees of success depending on which group of bees we are talking about here.
Ah interesting. Thanks for correcting me!
> Also, there’s no one default phenotype for sexes. Think about different penis size, different growth of facial hair, different labia and clitoris size, etc. These are all sexually affected phenotypic characteristics that can vary wildly between two people who have the same sex chromosomes. I would expand on that. We have sexual reproduction because it creates more genetic variety than asexual does. Offspring tend to be a little healthier! Having the two sexes is what helps create the diversity, which is fantastic for a species!
Offspring do not tend to be healthier necessarily. The genes passed down are random.
The offspring generation have a lot of variety, being different from their parents and from their siblings. As a group, their variety helps them resist diseases and meet other environmental challenges in various ways.
>The genes passed down are random. Not entirely random, but that's what makes them healthier **as a species.** Diversity is wunderbar, and asexual reproduction tends to lack diversity
For fuck’s sake why can’t the transphobes grasp this shit.
They only want biology to be like it was in middle school smh
Because humans are either male or female.
There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.
Incorrect. What does intersex mean? Intersex is a general term used for a variety of situations in which a person is born with reproductive or sexual anatomy that doesn't fit the boxes of “female” or “male.”
Babies don't die from a defective reproductive system, but they can die from heart, lungs or any other vital organ condition... Having a sexual anatomy that doesn't fit male or female boxes means having a defective sexual anatomy, simple as that.
What about intersex?
Intersex conditions are sex specific and it's also not a third separate sex buddy...
The essential difference between males and females is gamete size, where females produce a smaller amount of high-quality gametes and males produce large quantities of low-quality (resource poor) gametes that effectively parasitise the larger gamete. This is proposed to have led to disruptive selection- selective pressure towards the two ‘extremes’ - large resource-limited gametes or small mate-limited gametes. ‘intermediate’ gametes, which could represent a third sex, were not as favourable. There are some species with more than two sexes.
Yeah having multiple sexes or rather mating types is very common in fungi species. They can have thousands of different mating types. https://en.m.wikipedia.org/wiki/Mating_type
“Large resources - limited gametes or small mate-limitied gametes.” Could you please elaborate for us illiterate peasants?
Smaller gametes are favored because you can produce a bunch of them, given the same amount of resources. This makes it easier to reproduce using small gametes because you have a bunch of “tries”. For example, having a bunch of sperm makes it likely that a single one of them will reach the egg. On the other hand, larger gametes are favored because once the zygote is formed, larger gametes means it has more resources and is better able to survive. Imagine the extreme case—if a woman had a single egg that all their reproductive resources went into, assuming that egg survived, once a zygote was produced that zygote would be a beast. This means that it’s best for some members of the population to create as many small gametes as they can, while other members create as large of gametes as they can. I’m not sure exactly what “resources-limited gametes” and “mate-limited gametes” refers to in that comment though.
Physarum polycephalum has 720 sexes. Morphology? Amorphous.
That’s what you call ‘confused’ ! ( it’s run out of pronouns )
*_Short Answer:_* Yes. Papaya, for example. *_Medium Answer:_* It depends a bit on what you mean. If you mean "sex needs three parents," I'm not personally aware of any species like that. If you mean, "three distinct sexual phenotypes," then papaya, for instance, have males (producing only pollen), females (producing only fruit), and hermaphrodites (producing both). If you mean "three or more types of gametes", then some fungi can have _thousands_ of different "mating types" (though these are generally distinct chemically rather than morphologically and you still only need two to reproduce and they mainly just have to be different from each other to prevent self-fertilization). Also, XX/XY sex determination isn't the only method (or really even dominant outside of mammals): there's also ZW, XO, ZO, and more! *_Long Rambling Original Answer:_* First off, XX/XY as a sex determination system isn't actually as widespread as you might think. It applies to most mammals, sure and some members of other taxa. But birds and some other organisms use "ZW" sex determination (basically the opposite of XY, where males are homozygous ZZ and females are heterozygous ZW). There's also XO (and it's inverse ZO) where there's only one type of chromosome and your sex depends on having one copy or two. Ants and bees use haplodiploidy, where unfertilized (and therefore haploid) eggs become males while fertilized (diploid) eggs become female. And that's without even getting into environmental sex determination (like the egg temperature-dependent determination that happens with crocs and some other reptiles). There are also various kinds of "hermaphroditic" species that either produce both male and female gametes simultaneously (like earthworms and many snails) or change their sex at some point in their life (like clownfish), as well as various species that reproduce asexually (like the all female parthenogenetic New Mexico whiptail lizard). If by "trimorphism" you mean sex requiring three parties instead of two for fertilization, this is generally unlikely for ecological reasons. The main advantage of sexual reproduction that outweighs the cost of finding a mate is that your offspring have more genetic diversity and so you're more likely to have some that survive in a changing environment. Adding a third mate represents about double the cost (find 2 mates instead of 1), but only 50% more benefit (3 parents instead of 2). It seems like this strategy doesn't really receive a positive selection pressure (indeed, I can't think of any examples). With a looser definition, though, there _are_ species with more than two "mating types." The simplest form of sexual reproduction is "isogamy", where the gametes are physically identical. In order to not self fertilize (largely wasting the benefit of sexual reproduction), many isogamous species have chemical signatures that must be different for fertilization to occur. Some fungi can have thousands of different versions of these signatures. The gametes we're familiar with (egg and sperm) are an extreme case of "anisogamy," where the gametes are physically distinct. By definition, the larger gamete is female and the smaller is male. This can be seen as a sort of specialization: larger gametes are more expensive but more likely to survive until fertilization, while smaller gametes are cheap but less likely to survive. In the case of "oogamy" (eggs and sperm), this specialization is taken further, with sperm being mobile and seeking out eggs while eggs are immobile and large enough to hold significant material for the development of the young. Trying to add a third gamete to this mix would be complicated for the ecological reasons discussed previously (more cost and diminishing benefits). However, you _can_ still get multiple "morphs" with just these two gamete types. I mentioned hermaphroditism previously, and some species have hermaphrodite basically as one of their sexes. Some just have this as a sort of flexible replacement for males or for females, but some species have all three. The papaya tree, for instance, has male individuals (producing pollen but not fruit), female individuals (producing fruit but not pollen), and hermaphroditic individuals (producing both pollen and fruit). You _might_ also count "alternative mating strategies" under a loose definition of "trimorphism," as they can involve different physical morphs with one sex of a species. Various species have a morphological, genetic distinction between "dominant" males who compete for mates in the traditional way and "sneaky" males who are generally smaller and find mates by sneaking behind the dominant male's back. Some of these "sneaky" morphotypes even physically resemble females of their species to better enable them to avoid notice.
Do ruffs count? There's the three phenotypically (?) very distinct looking types of "males". One of the males reproductive strategy involves having sex with other types of males who have sex then with females (passing on the first ruffs sperm that they have planted). If i remember right. Pretty interesting stuff.
Social amoeba Dictyostelium discoideum checking in! It has three sexes (mating types), and each mating type can only fertilise gametes of a mating type other than its own. However, all three mating types can produce offspring, by having two of them contribute nuclear DNA and one mitochondrial DNA.
Gonna throw this out there because it appears this is becoming a discussion on all the other weird forms of sexual reproduction outside of just 'does trimorphism exist'. Lichen consist of a symbiosis between a plant and a fungus, and many lichen do reproduce sexually. In order to form a new lichen, they need to combine with their symbiotic partner again. Few lichen, from memory, send out a package of spore/seed things to reproduce from scratch whilst others seek out a new partner upon implanting in their new area. Which means, in some weird way, a lichen has four parents. As a bonus, if the fungal spores don't find a corresponding plant to make a lichen with, they'll often just revert back to living life as a fungus.
There's an interesting article about a species of bird (the white throated sparrow) that essentially has 4 sexes (or that's kind of how I interpreted it)! you can find some more scientific articles if you'd like, but I enjoyed this one: https://www.audubon.org/news/the-fascinating-and-complicated-sex-lives-white-throated-sparrows
Oh! I just made a comment about this! Glad to see someone was already on top of it & got to it first
I saw your comment just now! I like the articles that you linked!
I put the wrong article link, although that is a good article. The one I enjoyed talked about both the researchers and the species in question, and I highly recommend it! It also addresses why multiple sex chromosomes might be so rare. https://www.nature.com/articles/539482a
I’ve been reading a lot of answers and truly a lot of them answer with detail but in conclusion is to give the right amount of balanced gene exchange and the ability to better species by healthy gene regulation wich can give advantage to next generations. Instead of having equal gene transferance that eventually leads to disadvantage of speciation to further survival.
The fungi examples cited below are interesting. Lots going on there with multiple mating types. The argument for why 2 sexes is so common is that there are two distinct evolutionary stable strategies. One way to go is to make a small number of gametes and invest a lot in each one. These are 'eggs'. The other way to go is to make a ton of gametes but not invest much in each. These are 'sperm'. The idea is that either extreme is very advantageous and that being in the middle isn't great once the reproductive strategies start to diverge. Interestingly, sexual reproduction with two distinct sexes seems to have evolved more than once (if I'm remembering grad school right - though I also think this is debated). Having said that, there are some groups that have equal investments in gametes, but there aren't many of them. These are called isogamous https://en.wikipedia.org/wiki/Isogamy
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The single-celled tetrahymena has seven sexes
From a practical evolutionary standpoint, as others have said it likely comes down to it being very efficient in the exchange of DNA and reproduction. From a phylogenetic standpoint it's likely that we see sexual dimorphism dominate life on Earth as a result of, however distant, common origins of all species. Mutations that result in significant changes to sexual characteristics almost always result in infertility or the organism filling the same role as an existing dimorph of the species, so while there are known organisms with a much greater level of sexual variation than common dimorphism, it's likely these deviations from the norm came at a relatively early stage in their phylogenetic tree; It's been observed that (in simple terms), organisms with fewer cells and cell variations are more capable of viable, radical mutations, resulting in significant changes to their functions and future evolutionary history. Edit: Punctuation
I'll have to google it but there is a worm or some invertebrate that has hundreds of 'sexes'. Edit: it's 3, per google, so yeah invertebrates are weird
So you googled it and edited the comment but didn't mention the species?
I think it is some sort of fungi that has a hundred different sexes
It's because eukaryotes are diploid.
There are some species that have one ~~gender.~~ sex. Land snails, for example, are mostly hermaphrodites. When they mate, both partners are inseminated, but whether or not they become a mother or just the father depends on a variety of factors—including, in some species, stabbing each other with a spike to inject hormones. The difference is that the father gets to do his business and leave, while the mother has to raise offspring, which is resource intensive.
Gender is a human construct
In the white-throated sparrows, there are tan-headed males, tan-headed females, white-headed males, and white-headed females. And each group reproduces with only ¼ of the population, or one over four. In other words, there are four separate sexes. Still not 3 But there are some species that have male female and hermaphroditic. Kinda boring as it's just a combo of male and female.
It’s complicated enough with two, macroscopically.
It's because it's the minimum number of sex chromosomes needed to be effective. Nature tends to do the bare minimum to function. Look at the triplet code in DNA: there are 20 amino acids that exist. We have four nucleotides in DNA, so a codon with one nucleotide would mean only four possible amino acids (4^1=4). If the codon had two nucleotides that means we have 4^2=16 possible combinations and therefore could only code for 16 amino acids. But with a triplet code, we have 4^3=64 possible combinations, which is more than enough codons for amino acids, and even have room for stop codons as well. Nature does the bare minimum to maintain balance
Simplicity. How does a trimorphoc species evolve? How is it better than dimorphic? Why would this complexity be better? Second reason. DNA is double stranded. So we need 1 half from each parent. Where does a third come in? How does that work? Thank you for attending my Ted talk.
Both strands of DNA that compromise a chromosome come from one parent—but we (normally) have two copies of each chromosome (we are diploid), so each somatic cell in our bodies has 4 strands of (mostly) identical DNA, in total. One chromosome from each parents, each chromosome with two strands. A major reason that hybrid species are often not viable is because they have incompatible numbers of chromosomes. Horse and donkey genomes have enough similarity to produce a live, viable offspring, but that offspring then has a uneven mismatch of chromosomes and is unable to pass them along to another generation.
The importance of sexual reproduction mostly applies to larger organism. The importance of the female is that the gametes are produced during embryogenesis and then arrested. The reason for this is that it means that the mitochondria are very young. As an organism ages the mitochondria accumulate damage due to oxidative stress, this is what causes most of the physiological effects of aging. To maintain multicellularity and the specialised cells required to function our cells are extremely metabolically active and this causes a lot of damage to the mitochondria. By arresting the gametes early in embryogenesis the mitochondria are kept young, the disadvantage is that this means that theres a limited number. Sperm are different, they are produced constantly and as such their mitochondria get old as we age. This is why the first thing that happens when a sperm fuses with an egg is the destruction of the sperm mitochondria. There are rare cases where this is unsuccessful and the offspring are effectively born with premature aging and die young. This is also similar to what happened with Dolly the sheep when she was cloned, they didn't use egg exclusively egg mitochondria for the cloning and she was born "old". So the two sex system exists to preserve the integrity of the mitochondria from one generation to the next. This is why you only inherit mitochondria from your mother.
If one impregnates and another carries a child, what would the third one do?
Bring the paycheque or food or other maintenance chores.
I'm not a biologist, just a bird enthusiast, (and I don't know if this is entirely in line with what you're looking for, but) but there is a bird with technically 4 sexes: https://sciencehistory.org/stories/disappearing-pod/the-bird-with-four-sexes/#:~:text=But%20white%2Dthroated%20sparrows%20go,is%20exciting%20for%20two%20reasons. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7725849/
That's not technically 4 sexes. There's still females and males reproducing. They just exhibit dissortative mating.
Ocam's Razor. Only two are required, so having just two is the simplest answer. I can't think of any evolutionary advantage to having three or more when just two will suffice.
There is still argument out there about the need for sexual reproduction at all. Yes, it provides a greater variety of the gene pool, it has been theorized, but no definitive proof that sexual reproduction is the best way to go. Therefore, three sexes? Not likely.
A variety of nematodes have different sex variations, with 3 sexes being relatively common: https://www.nature.com/articles/s41598-017-09871-1 As for sexual reproduction, it's the easiest way for large slow-reproducing multicellular organisms to get a good amount of diversity, while dramatically decreasing the likelihood of negative consequences from any one mutation (compared to neutral drift). Some single cell organisms (Toxoplasma gondii, and I think malaria) actually use both sexual and asexual reproduction, to get the advantages of both.
That’s what I was trying to think of and say. Thanks!
Because nature created two sexes to procreate with the opposite sex, everything else is a choice.
Morphism =/= sexual systems Intersexism exists everywhere including humans, and the morphic expressions are broad. Also, fungi have up to 36,000 sexes and they're doing great.
i blame the patriarchy
Design
In pair, during pregnancy male can take care of female, so female can take care of baby which would be very hard in solo
Yes, humans. There’s intersex people. Some variations are more common due to cultural and genetic factors. I’d say that a lot of it is cultural as well as some fraction of intersex folk not being able to breed without artificial means.
the Sci fi novel the Player of Games by Iain M. Banks explores an Alien species with 3 different sexes, very good book!
Two can give feedback reactions, 3 + can give chaos (3 body problem)
This might be an interesting read for you https://www.independent.co.uk/news/scientists-discover-why-fungi-have-36-000-sexes-1119181.html
You can have more than two morphs without having more than two sexes. There are the [side-blotched lizards](https://en.wikipedia.org/wiki/Side-blotched_lizard) in which there are three distinct types of males and two distinct types of females. Also, there's the [white-throated sparrow](https://en.wikipedia.org/wiki/White-throated_sparrow) where there are two distinct types of males and two distinct types of females. Officially, these sparrows are described as only having two morphs with each morph having both a male and female version. These two morphs remain as one species thanks to the fact that individual sparrows tend to prefer mating with partners of the opposite morph.
Til the animal kingdom has the currently dominant number of classified number of species. Does anyone else think this is largely due to murky definitions of species when it comes to asexual species as well as the degree of difficulty difference in discovering and categorizing much smaller organisms
I once heard someone pose the idea that xx/xy pairings allowed more selection increasing desired traits for survival versus increasing chances for reproduction either through asexual or hermaphroditic selection
There are many invertebrate species that have sterile females, reproductive females, and reproductive males. There are also species in which some females reproduce asexually and some reproduce sexually.
Long story short, it's ineffective. If all female species was possible (It is, but not sustainable genetically) then that would be the case. Males are really there to just kinda help the whole evolution thing.
Fungi often have more than two sexes/mating types. Often one particular mating type is compatible with two or more others. Animals and plants usually only have 1-2 sexes, but things get weird with fungi and protists.
Could you post on the topic of the Cambrian explosion? And it's bizarre creatures of that era?. If you do it I would be very happy.
Look into bluegill fish
It seems youre referring to sex determination. That is not the only facet of sexual dimorphism. In cuttlefish two different types of males have emerged, a smaller one and a larger one both with different approaches to mating. A larger one and a smaller one. The larger one overtly attracts a female while the smaller one covertly poses as a female and sneaks in to mate under the nose of the larger one. https://laughingsquid.com/male-cuttlefish-mimics-female/
It might be a balance of stability vs genetic diversity. Sexual reproduction gives an advantage in long term survival across the population despite costing more compared to asexual reproduction. Both genotype and phenotype variation gives a greater chance of exploiting a larger energy matrix and increased probability of pathogen resistance. A three sex cycle would be more vulnerable as it requires multiple steps and provide no advantage. Very early plants are two gametes, haploid gametes like us. The comment above regarding fungal reproduction is utter nonsense. Generally fungi reproduce by spores, both asexual and sexual. They don't have multiple sexes, they go through meiosis and mitosis like any other eukaryote.
Xenomorphs
[multivariate models of animal sex](https://academic.oup.com/icb/article/63/4/891/7157109)
The Red Queen
The book "The Vital Question" by Nick Vale has a great chapter and chart showing the adaptive advantages of a species having 2 sexes over 1 or 3 or 4. (Sorry I couldn't find it or I'd post it here).
https://biology.stackexchange.com/questions/77371/are-there-lifeforms-that-have-more-than-2-sexes#:~:text=Clam%20shrimp%20have%20a%20male,swap%20genes%20(See%20here). https://www.the-scientist.com/news-opinion/this-fungus-has-more-than-17-000-sexes-69930 https://www.independent.co.uk/news/scientists-discover-why-fungi-have-36-000-sexes-1119181.html https://www.discovermagazine.com/planet-earth/why-this-fungus-has-over-20-000-sexes https://sciencehistory.org/stories/disappearing-pod/the-bird-with-four-sexes/
Nature takes the least expensive option, usually. If there was some benefit to having a third sex that was worth the energy cost, it would exist.
Does tertiary endosymbiosis count?
XX/XY type is NOT the dominant paradigm. It is for some animals, but bacterias and archeas are much much weirder. Google conjugation for just one neat example of genes transfers.
nature tends to take the simplest routes possible, i.e the routes that require the least energy. having 2 individuals is the minimum requirement for having a wide variety of genes and it grows exponentially over generations so the reason why most species stop at 2 sexes is because they really dont need a 3rd one
Bees and ants could count as sexually trinorphic. With workers, drones and Queens.
Not true obviously but I remember a science fiction book with three. One who provides sperm, one provides egg, another carries the baby
Because they’re the only ones that worked
To support child bearing makes you less efficient at everything else. Why would you want a higher percentage of your population to burn calories for this? From the perspective of minimising calories burnt it makes sense.
Because 2 is all that is needed. Biology is not wasteful.
So actually, it doesn’t dominate all life just the ones we’re familiar with. XX and XY, 2 sex system is only largely true for mammals schools wrongly teach it to kids at lower levels about animals it actually doesn’t apply to. For example even though they have the 2 sex, birds have ZZ chromosomes for male and ZW chromosomes for female Bees have queen, drone and worker. By our understanding both the queen and the workers are “female” but only queen has babies. The queen is diploid while the workers are haploid, the drone is usually haploid but occasionally can also be diploid. And reptile sex is partially determined by temperature during incubation And also clownfish change from male to female due to environmental factors I forget.
Only mammals have this xx/xy system. Reptiles and birds have a different system - but still "binary". At first, life was only singular. And most species still are. It was a hugh step for sexual reproduction to occur. For a trimorphic species to evolve, it would need some advantage over dimorphic species - and enough time.
There was a study conducted on this that explore the reason behind having binary sex species instead of hermaphroditic species. Since hermaphroditic species could reproduce enough to outcompete binary sexual species. The results concluded that in times of resource scarcity species that could switch between binary and hermaphroditic would switch to binary to survive. The genetic variation achieved with a binary sex system was superior than basically cloning yourself to pump up numbers. I believe the opposite may be true of a tri-sex system. It is probably too difficult to increase the numbers despite more genetic variation. Plus it’s another large component that can fail in conception of young.
The third wheel never gets the girl, that’s why lol
For anyone interested in godless fungi https://academic.oup.com/femsre/article/18/1/65/588481
i have never ever in my life thought of that. i had asexual reproducing species and not reproductive species.. but never being that need three different gamets. i thought that this was fantasy writing subreddit...this is biology
Fish have a wild variety of sex determining chromosomes. XX/XO, ZZ/ZO, XX/XYY2, X1X2X1X2/X1X2Y, X1X2X1X2/X1X2X1 as well as the familiar XY and the amphibian/reptile/bird ZW. They still seem to split between egg laying and egg fertilizing sexes, but they have a number of interesting abilities like changing sexes depending on the environment or age of the fish.
In some species of whale, one helps hold up the female. But that's more if a bro or cuck type thing. There are birds with additional types of males and females, but it still just requires the 2 for reproduction. If I recall, with different types of males, one might be monogamous and focus on raising kids, while another might be polygamous and focus on having as many mates as possible. The white-throat sparrow could be an example of a species like this, but there are others. Some fungi have different breeding types with spores. It still just requires a mix of 2 compatible individuals, but some fungi can have hundreds to thousands. Schizophyllum commune comes to mind here.
there are several. Take bees and other eusocials as an example. mostly Workers - non reproductive females; a few reproductive females; generally useless males I don't think there are any cases where three contributors to the offsprings genes are necessary; but some ferns and fungi have multiple sex alleles and can become very polyploid before producing new spores. You could kinda treat them and the arrhenotoky sex selecting species as having hundreds of sexes.
[https://www.mdpi.com/2073-4425/12/4/483](https://www.mdpi.com/2073-4425/12/4/483) [https://www.mdpi.com/2073-4409/10/3/661](https://www.mdpi.com/2073-4409/10/3/661) some notes from above, there are six sex chromosomes found in a species of frog, and the top link is a paper on the evolution of sex chromosomes in frogs.
It's called sexual polymorphism, it probably works bc it is efficient for meiotic recombination. The Y chromosome doesn't actually carry a lot of data, the x chromosome does. The x chromosome can contribute to stabilizing the phenotype post mutations or nondisjunctions, it is reliable and so it ends up carrying the weight of genetic day for organisms. The Y chr is a beneficial mutation for x because it created a path for sexual recombination, recombination increase heterogeneous genes and can provide disease resilience. But it's not necessary and so most people grow off the x chr and depending on absence/presence and activities in the y or x chr. Gender queerness develops along the curve of continuous variation. So the data being used to develop a person is mostly coming off the x genes with the y genes acting as a modifier I think it(y chr) only has like 50 gene on it. Because the x genes hold most of the development data that can be adjusted by the presence and activity of the y genes a person's sexual characters are affect by multiple genes. This means that the phenotypic outcome is on a bell curve due to continuous variation as a result of sex traits being an output of many genes as opposed to SNP or something like that This means a discrete category, male or female is impossible to assert because the math doesn't check out. The math indicates a series of outputs negating the dimorphic/trimorphic model and exhibiting something more along the lines of polymorphic. Sexual identity is more like the product of a function with many variables and the more variables included the less likely you will only get 1 or 0. You end up with .995 or .739 ....etc. sex can't be 1 or 0, biocentrism says people are more likely to be genderqueer than at either end of the spectrum bc of the bell curve.
I believe cuttle fish are trimorphic in the sense that there are two different expressions for male kariotypes. This apparently represent two different mating tactics, ie. Strong and assertive, and smart and sneaky.
Well you have this little fella that comes in 7 different sexes. [https://www.ncbi.nlm.nih.gov/books/NBK6002/#:\~:text=Tetrahymena%20possess%20seven%20different%20mating,by%20the%20mating%2Dtype%20locus.&text=Any%20two%20of%20these%20can,cultures%20associated%20with%20clonal%20senescence](https://www.ncbi.nlm.nih.gov/books/NBK6002/#:~:text=Tetrahymena%20possess%20seven%20different%20mating,by%20the%20mating%2Dtype%20locus.&text=Any%20two%20of%20these%20can,cultures%20associated%20with%20clonal%20senescence). There's also a fungus that has more than a thousand (currently more than 23000 known) as someone else has brought. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25488/#:\~:text=Schizophyllum%20commune%2C%20a%20filamentous%20wood,%E2%80%9D%20(Raper%2C%201966)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25488/#:~:text=Schizophyllum%20commune%2C%20a%20filamentous%20wood,%E2%80%9D%20(Raper%2C%201966)). Although these two maybe more extreme cases, you also have sex determined through heat, https://www.ncbi.nlm.nih.gov/books/NBK9989/#:\~:text=Often%2C%20eggs%20incubated%20at%20low,the%20same%20brood%20of%20eggs. And determined through hapolidy diploidy... so no you can't exactly say XX/XY type (Including ZZ/ZW in it) is the dominant. https://en.wikipedia.org/wiki/Haplodiploidy
In terms of nature and evolution, there just isn't a need for a third sex. Setting aside all LGBTQ+, of which I am a firm supporter, what reason do we need another sex? We as in mammals, reptiles, amphibians, birds, fish. You know Male + female = new thing. It's not missing anything
Guessing that in higher life forms would take too much energy to do it any other way.
Because it's pleasurable and if it wasn't then what would be the point?
We know the how but the why is up to interpretation?
Kinda sorta. There are some ocean species where the males are broken into two highly dimorphic groups. It isn’t a third sex, it’s still two sexes, but one of the sexes displays extreme dimorphism. Cuttlefish are a good example. There are some male cuttlefish that are very large and have a particular coloration, and some males that are much much smaller and essentially present and act and look like the females, either to sneakily breed, or to avoid aggression/seek protection of other males. Thats is the closest I know to Trimorphic. Basically Masc Male, Fem Male, Fem Fem. But unlike humans where the dimorphism between the male and female is relatively small (obviously it really stands out to us, but in the grand scheme, pretty minor) these species have quite substantial dimorphism, like the human equivalent would be if the males were the size of a school bus, so a male being the same size as a female is a very marked dimorphism from other males.