How do we draw the line between species, exactly? Similar to this, you can distinguish between races and genders with skeletal tendencies now, but we're all one species. So when they are compatible enough to bone each other and said boning yields offspring, what exactly determines the line between 2 species and 2 distinct populations of 1 species?
edit: I'm also always intrigued by statements like this: "Interestingly, they suggest that 6%-7% of the genomes of West Africans is archaic in origin". I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees and don't even have the same number of chromosomes. So there's a lot more than that we have in common with some archaic species, and a lot less that we'd expect to have with closer relatives.
The idea of discrete species is just a useful approximation to help us think about things. And it's an extremely useful first cut, imagine how confusing a farm would be if you didn't mentally keep chickens and bulls in different boxes.
But when you look closely enough, there aren't really any such exact groupings in nature. Conception only involves the DNA of two individuals, not some larger group. And we know that species today have common ancestors, and it can't be that there was a precise second at which they became distinct, every split must have happened gradually.
(Like us, animals also have their own heuristics about other animals, including what sort of things they will mate with, but it's imperfect. Denim jeans cannot reproduce with poodles, as it turns out.)
I've looked into this, and there's no great way to do so, becuase the concept of species really just means large morphological changes. We assume everything is taxonomized (a tree), but in reality there is no tree--sometimes there is cross polination after some time apart. Ultimately they have a precise set of morphological criteria for each species, and they arrive at this criteria based on a sampling of animals and associating their morphology with their DNA.
They also use string similarity algorithms to determine morphological order, so we don't strictly know the order at the most precise level.
Of course, this is all very controversial, some people think we're always changing gradually and some people think we always change rapidly. I think they're both wrong--sometimes organisms change rapidly, and sometimes they change rapidly, depending on environmental factors.
disclaimer: I'm no expert, I've just looked at it from an algorithmic view and read some taxonomical texts as I had the same question as you.
The further you zoom out, the more tree-like it gets, but if you zoom in on any particular node in the tree, like hominids, then it becomes a tangled mess.
It's my vague impression that you get species that can't interbreed after extended geographic/habitat isolation. But short of that, it's a tangled mess, with complex fertility patterns.
I remember learning this vaguely as well, it's just a relatively useful rule with lots of exceptions, but it is not a law--it happens even after extended isolation: https://en.wikipedia.org/wiki/Hybrid_(biology)
As an amateur I'd hypothesize if the species diverges and then relocates, but is subject to similar environmental pressure, the morphological changes won't be great enough to prevent the organisms from interfacing and then reproducing.
We've determined this through string similarity algorithms, so really I'd say we can't be completely certain here either.
"Essentially, all models are wrong, but some are useful."
As to the 6% thing that's in the the same sense that you got 50% of your genes from your mother. Most of the genes there will be identical to the ones your father has on a codon by codon basis but their origin is your mother. And by looking at the 1% of genes where humans vary from each other we can tell which genes came from this ghost population.
>How do we draw the line between species, exactly? Similar to this, you can distinguish between races and genders with skeletal tendencies now, but we're all one species. So when they are compatible enough to bone each other and said boning yields offspring, what exactly determines the line between 2 species and 2 distinct populations of 1 species?
You can't. In practice, extinct branches of humans are classified as separate species, and animals are classified as a bunch of species because biologists get credit for discovering new species. In contrast, living branches of humans (e.g. bushmen vs. pygmies vs. everyone else) ar classified as a single species even if they have evolved largely in isolation for hundreds of thousands of years and rarely interbreed, because classifying them separately could give ammo to racists and worse.
>I'm also always intrigued by statements like this: "Interestingly, they suggest that 6%-7% of the genomes of West Africans is archaic in origin". I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees and don't even have the same number of chromosomes. So there's a lot more than that we have in common with some archaic species, and a lot less that we'd expect to have with closer relatives.
It usually means 6-7% of genes that vary between humans.
> In practice, extinct branches of humans are classified as separate species
They were classified that way, until the presence of Neanderthal & Denisovan DNA was discovered in modern humans.
> In contrast, living branches of humans (e.g. bushmen vs. pygmies vs. everyone else) ar classified as a single species even if they have evolved largely in isolation for hundreds of thousands of years and rarely interbreed
They are classified as a single species with the rest of humans because they can interbreed with other humans, not for political reasons.
We couldn't draw the same conclusion about extinct branches until recently because we don't have living groups of them that we can observe interbreeding. Now that we see the genetic evidence of that the classification has changed.
> They are classified as a single species with the rest of humans because they can interbreed with other humans
This is not the standard for, e.g. birds, however. Consider the mallard. It's happy to breed (with fertile offspring) with just about any duck. However the ornithology community does not say "great, they're all ducks, maybe with separate subspecies". Instead they complain about "genetic pollution" wiping out species of ducks through genetic drift.
Myself, I think it would be perfectly reasonable to call these subspecies and keep the Biological Species Concept[1], but in actual usage the Biological Species concept is dead.
In the past the rules for 'species' was not whether or not they will interbreed, but whether or not their offspring would be fertile.
A horse and a donkey can breed just fine, but a mule cannot.
This makes sense because we know that species eventually differentiate and whether or not they can recombine is a good indication of how far apart that separation is.
But nowadays all that stuff is thrown out of the window. I don't really understand why it is no longer considered a useful distinction.
The Hawaiian duck isn't racist enough in choosing mates so now conservationists want to bring back more genetically pure Hawaiian ducks through selective breeding. It's rather ridiculous.
First, many organisms reproduce asexually and are thus classified into species on other grounds. Second, animals that have the ability to produce fertile offspring with each other are still often classified as separate species or at least subspecies (depending on whose definition you use) if they don't customarily interbreed and have differing appearances / characteristics.
> I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees
Those percentages aren't measuring the same thing. Chimp to human is a total genome comparison. Human to Hominid ancestor X is based on identified humane genes. The latter is a tiny subset of the former.
They will have different sex chromosomes (Y from tiger or lion) and different mtdna. So there might be some slight differences. And it's not out of the question that one is more viable than the other.
EDIT: Wikipedia: "Notably, ligers typically grow larger than either parent species, unlike tigons"
You are trying to take an interesting discussion about species off on a wildly irrelevant tangent. There is no sexism here and the names are not designed to promote patriarchy.
It's off topic and inflammatory. And this follow up comment reinforces the appearance that the point is basically shit stirring and nothing else.
I talk about sexism pretty regularly on HN. Sometimes it doesn't go well and sometimes it does. You absolutely can discuss sexism here. This is just not a good approach to doing so.
Yes, that’s arbitrary; unless we decide to always make the sexes explicit, we have to make a choice as to whether to mention the male parent or the female parent first.
Hoever, just as with Liger and Tigon, the two donkey/mule variants have different names:
Male Donkey (jack) + Female Horse (mare) = Mule
Female Donkey (jenny) + Male Horse (stallion) = Hinny
Well obviously one or the other needs to go first. Why do you think the first one was chosen because it has the greater honor? If it was the other way round, wouldn't it look just as patriarchal to you ("Ladies first" and all that)? And are you sure they didn't flip a coin to see which parental gender would go first?
I don't know how they made the choice, of course. And if you have sexism on your mind, there isn't a right choice in this situation, I agree. However, if you take stock of all the similar choices (male or female) that we make in these mundane contexts, would it come out even? Or would it lean heavily to one side?
As others here have noted, it's generally or historically been deemed to be a pairing expected to produce a fertile offspring that can interbreed with others of the same group.
Though, really, DNA is just two RNA. We are made up of the same code that makes bacteria and even viruses. So it's bound to be messy and highly hackable.
I found an article written in 2013 and it was an interesting read. But it seems the author was not aware that domestication also leads to a change in physical appearances in every animal we know thus maybe cause and effect are reversed?
In a recent episode of the Grand Tour locals from Colombia were proud to fuck their donkey so I didn't want to dismiss this hypothesis on forehand.
We do have to discuss and reason about living creatures with other humans though, so it's helpful to name and categorize, just know that the names and categories are a human language construct, nothing more.
Just because you can define a group, doesn't mean that's inherently divisive. Like you mentioned, species are approximately defined by their ability to mate and produce offspring, as part of a larger taxonomical hierarchy but certainly not exhaustive on its own.
> when they are compatible enough to bone each other and said boning yields fertile offspring
This was a definition of species for a long time. In recent years some have advocated for changing it a lot, to the point that they should just start calling different dog breeds their own species.
Or to go the other way, are dogs and wolves different species?
Is it homo neanderthalensis and homo sapiens or homo sapiens neanderthalensis and homo sapiens sapiens?
In my opinion, Denisovans and Neanderthals are both obviously types of Homo Sapiens and the argument they aren't is at this point mostly promoted by those desperately clinging to the now disproven out of africa hypothesis.
What? When was it disproven? There's evidence of interbreeding outside of Africa with other species, in some sense of that word, which also originated in Africa, right? Maybe I missed something.
The strongest version of "Out of Africa" or "Recent African origin of modern humans" is "Modern man developed in Africa, and then spread throughout the world, essentially unchanged, completely eliminating other archaic hominids". Given known interbreeding with other hominids, this is clearly false, or at best incomplete to the point of being misleading.
This is in contrast to a "Multiregional origin of modern humans", which still has "expanding from Africa" first, but far before modern man developed, followed by evolution and development everywhere without modern features coming from Africa "all at once". This too is clearly false and misleading. There were large migrations from Africa with large genetic distances from the native hominid populations, and the resulting mixture appears to be much closer to African than the native hominids.
The modern synthesis is multiple waves of expansion out of Africa and significant gene flow making the tree look more like a river delta: lots of forking but also lots of merging, though not to the point of an undifferentiated sea either. The exact details are constantly being reevaluated as more genetic data is acquired. This is significantly different from the strong Out-of-Africa hypothesis, but claims there have weakened to include essentially this picture. The difference between the two point of views is a matter of scale at this point: how strong are the waves out of Africa, how much was displacement vs interbreeding, how much do genes flow in patterns besides out-from-Africa, how much is one giant expansion a reasonable approximation, etc.
edit: I'm also always intrigued by statements like this: "Interestingly, they suggest that 6%-7% of the genomes of West Africans is archaic in origin". I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees and don't even have the same number of chromosomes. So there's a lot more than that we have in common with some archaic species, and a lot less that we'd expect to have with closer relatives.