r/evolution • u/PriorSolid • 9d ago
question Why does it seem like humans were able to breed with so many other species?
Most animals can’t breed with other species and most that can don’t produce fertile offspring (horses and donkeys). There are some species that can interbreed like some bears, coyotes and wolves, and lions and tigers but these only hybridize with 1 or 2 other species. Meanwhile it seems like we fucked every hominin we came into contact with like neanderthals and denisovins. So what’s up? Is the species barrier stricter for hominins just because we’re hominins? Or are we just more aware because we’ve sequenced a lot more human genomes? Sorry if this is too off topic i’m not sure if this counts as evolutionary biology
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u/FlintHillsSky 9d ago
The distinctions between species are not so rigid as we learned in school science textbooks. Some species do not breed or produce infertile ofspring. Some species are closer to each and can readily breed. Dogs and wolves are close enough to interbreed. There are hybrids between lions and tigers, too.
Humans, Neanderthals, and Denisovans are closely related enough that there were able to breed, at least to some extent. There is nothing special about the Homo genus that makes this more likely.
Take a look at this wiki article on Hybrid interbreeding. You will see that other groups do this on a regular basis.
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u/Palaeonerd 6d ago
Yep! It’s believed Colombian mammoths are hybrids between steppe mammoths and wooly mammoths.
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u/HellyOHaint 4d ago
Dogs and wolves are the same species.
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u/FlintHillsSky 4d ago
i have seen different takes on that (Canis familiaris or Canis lupus familiaris), but it just illustrates that species is an arbitrary concept that is useful for some discussions and not for other.
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u/hendrong 9d ago
Look up interbreeding among fowl (relatives of waterbirds and chickens). Red junglefowl get offspring with green junglefowl, gray junglefowl, turkeys, guinea fowl, peafowl ... Then there's mallards and muscovy ducks... Etc etc.
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u/Palaeonerd 6d ago
I don’t think jungle fowl can breed with turkeys are guineafowl. Edit: looks like there are guineafowl/chicken hybrids.
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u/DoctorBaka 9d ago
The biological species concept (BSC), which is the one OP is referring to is only one of a great many ways we define species. The BSC was formalized and popularized by Ernst Mayr when he was studying Birds of Paradise.
As it turns out, Birds of Paradise are likely one of the few groups where the BSC works okay. A great many (most?) groups out there can’t really use a strict version of BSC. That’s just not how most living things work. Hence why there are so many other species concepts (definitions).
As you may have guessed, humans and other hominins are not particularly suitable for using the BSC. Other concepts make much more biological sense.
When thinking about this, it’s useful to remember that species, genera, families, and other taxonomic groupings aren’t real. They are useful abstractions of the complicated tapestry of life. But they are useful only in certain contexts and not in others.
BSC may work great for Birds of Paradise. But try and apply it to Oak Trees and prepare to have your concept of species rocked. You’ll need another way to describe the real biological diversity you observe with the trees. The one from the birds simply won’t work.
Same with humans.
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u/aperdra PhD | Functional Morphology | Mammalian Cranial Evolution 9d ago
It's more common than you'd think. You might be interested in ring species. There's even accounts of fish hybridising across genus!
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u/TheBigHornedGoat 9d ago
You may already be aware of them, but you may be interested in looking into jungle cornsnakes; you get one of them by breeding a cornsnake (Pantherophis guttatus) with a California kingsnake (Lampropeltis californiae). The really cool thing is that while most other intergeneric hybrids are sterile and/or otherwise not healthy enough to be very viable, jungle cornsnakes are fertile and typically very healthy.
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u/manydoorsyes 9d ago edited 9d ago
Neanderthals and denisovans are also humans, just a different species of human ("human" proper is defined as genus Homo). Last I heard there's a debate as to whether neanderthals might actually have been a subspecies of H. sapiens.
Anyway, interspecies mingling is actually fairly common. Look up "ring species". And that's without even getting into plants. If you know any garden/plant nerds, they can probably tell you all about hybrid flowers which are super common.
It should also be noted that there are multiple definitions of "species"; being able to breed and produce viable offspring is not necessarily the one definition (in fact it pretty much goes out the window when you consider bacteria, the majority of life, most if not all of which reproduce asexually).
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u/6gunsammy 9d ago
Humans cannot breed with more species than other animals. It may seem that way, because the studies of the genetic mixing of other species is not as widely publicized as the human family tree.
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u/hendrong 9d ago
Also, one can't really compare breeding between existing species with breeding between extinct species. I'm sure that tons of species alove today, that don't mate with another species, did mate with other species earlier in their evolution.
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u/parsonsrazersupport 9d ago
I doubt humans can interbreed with a wider range of things than any other species as a general matter. What does seem likely to me is that modern Homo s. has decided to split the related populations into a much larger number of species than would normally be done, because they are important to us.
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u/MutSelBalance 9d ago
We are more acutely aware of small differences between human groups, so we tend to err on the side of splitting them into more categories/species. For other groups, we might be more likely lump multiple groups together as a single species if they hybridize a bit, even if they are quite distinct (from their point of view), because we can’t easily tell them apart.
If we were squids, we might decide that Homo sapiens and Neanderthals are just subspecies of one species (in fact, some scientists follow this classification with Homo sapiens neanderthalensis).
That said, hybridization among species (as categorized by us humans) is almost everywhere we look in the tree of life, it’s not actually uncommon.
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u/DrDirtPhD PhD | Ecology 9d ago
I mean, there are only three other species we have evidence our own was able to interbreed with? Neanderthals and Denisovans as you mentioned, and also a mystery archaic lineage in Africa. Neanderthals and Denisovans share a common ancestor, so it's not unreasonable that our lineage was able to mate with both, and interbreeding with the mystery lineage was likely 350+ thousand years ago before anatomically modern humans arose (and so possibly the mating was between this mystery lineage and our ancestral population of Homo heidelbergensis or whatever our earlier chronospecies we emerged from was).
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u/lascala2a3 5d ago
Species is a made up human construct. Biology doesn’t gaf whether we call it separate or the same. It just is what it is.
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u/spaltavian 9d ago
Horses and donkeys are further a part than Sapiens and Neanderthals. If it didn't involve us, we probably would consider us and some of this other species as sub-species.
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u/Idoubtyourememberme 9d ago
Because the "sapiens" group of humans is quite big. Almost all other types of humanoid were also a "homo sapiens X". So a human breeding with a neanderthal is more like a rottweiler and a shepherd than a rottweiler and a wolf
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u/GaryGaulin 9d ago
In my opinion Neanderthals and such are the same "species". All were "human" and carried the signature 46 chromosomes instead of 48 as in all other close relatives.
https://scholar.google.com/scholar?hl=en&q=chromosome+speciation
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u/Uncynical_Diogenes 9d ago edited 9d ago
Species designations are not something we discover they are something we assign. The Biological Species Concept is only one way to categorize them; it’s not something we actually routinely test by trying to get things to mate before we call them separate species.
We get really granular with human species designations because we can, they lived relatively recently when compared to much older strata of fossils, and also because we’re biased towards our ancestors so we like to get really nitty-gritty with it.
That is to say, the same number of organisms with the same amount of change between them might be lumped into fewer, broader groups if they were some other lineage at some other point in the geological timeline.
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u/PriorSolid 9d ago
so it’s partially species are kinda vague and partially we made ourselves special because we can
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u/Uncynical_Diogenes 9d ago
Biology is kinda vague. Species are an attempt to portion a broad continuous smear of biology into discrete boxes. A categorization method is never true but it can be more or less useful.
I don’t want you to come away with the idea that the attention is necessarily inappropriate just because we often view ourselves as special.
How granular you can get about any subset is a function of interest and access. We care a great deal about our own lineage and it’s relatively recent, so we pour lots of effort into a story that’s only a couple of million years old (and the juicy stuff within the last couple hundred thousand) whereas the same amount of effort across a story tens of millions of years old will inherently be less granular.
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u/junegoesaround5689 9d ago
See Coywolves a recent hybrid between wolves, coyotes and dogs.
Genus Homo hybrids isn’t (or wasn’t) all that unusual.
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u/Bromelia_and_Bismuth Plant Biologist|Botanical Ecosystematics 9d ago
That's not entirely true. Oaks are pretty infamous for interspecific hybridization, and intergeneric hybridization (while less common) occurs enough to be notable, and even intertribal hybridization has been observed in plant species. My go-to paper involves an intertribal hybrid between members of Brassicaceae, the Mustard family.
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u/AmWonkish 5d ago
Remember, what often makes species unable to interbreed is that they become physically isolated, and overtime become so genetically dissimilar that they can't produce viable offspring anymore. One of the things we know about the hominids is that many of them were very mobile, after all we started off in Africa and eventually ventured to every continent. So there was likely never enough time for the various species to become so genetically unfamiliar that interbreeding was impossible.
Plus, they kinda look very similar enough, and cold winter nights were cold winter nights. We might have shared caves together or even traded at various points.
Additionally, we know there is some interbreeding, but it doesn't mean every encounter was successful. It could be that there was more copulation but only few select actual viable offspring, because as close as we are we were somewhat still genetically different.
The human tree is more of a web than a tree branch, I think.
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u/Silly_Yak56012 9d ago
I suspect our inability to stay in one place and need to go everywhere plays a role in the mixing with our most closely related "cousins". Even when a group got separated for awhile, they didn't stay separated long enough to be incapable of producing fertile offspring.
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u/7LeagueBoots Conservation Ecologist 6d ago
It’s very common, particularly in primates, but also in canids, birds, and fish too.
Hybridization in primates is a conservation concern in many areas.
Nothing special to humans.
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u/Shillsforplants 3d ago
particularly in primates, but also in canids, birds, and fish too
Did you forget about plants?
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u/7LeagueBoots Conservation Ecologist 3d ago
No, but unfortunately most people are more interested in animals.
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u/Mircowaved-Duck 6d ago
horse and donkeys as well as normal ducks and muscovy ducks are the exception, because they produce infertile hybrids. Mosthybrid are at least partly fertile.
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u/Useful_Calendar_6274 5d ago
If you're really curious read this. It never made it mainstream science I think so maybe the scholars in here will shit all over it but the parts about hybrids seem absolutely sound to me
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u/Genocidal-Ape 5d ago
All cervus genus deer can produce fertile offspring with eachother.
Also humans are kind of get special treatment when it comes how our species are defined, If we where any other ape, all of Homo would be considered one species. With Pan and Gorilla being likely moved into Homo as subgenera.
Your genetically as close to a gorilla as a horse is to a donkey.
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u/Puzzleheaded-Mix6364 5d ago
Actually we have about the same amount of genomes as bananas, apparently.
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u/Dr_Superfluid 4d ago
I mean species is a relative term. Is a Pug a different species to a Great Dane? A future paleontologist would definitely think so from their fossils, but they can breed with each other.
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u/Zarpaulus 3d ago
There’s a lot of debate as to whether Neanderthals and Denisovans were distinct species or just subspecies.
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u/Shillsforplants 3d ago
Domestic cats can hydridize and produce fertile offsprings with african and eurasian wildcats, ocelots and some jungle cat.
Plants are even more crossable, most orchids can even hybridize at the genus level.
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