Thursday, September 22, 2011

Comments: Species Demarcation.

Kay asks:
Explain this for me if you will. The other day I saw a post from a creationist stating that the Theory of Evolution has to have some fault in it because there is no interbreeding of species. How in layman's terms did the first humans evolve from apes and then proceed to separate themselves from the apes? At what point did breeding with apes stop by humans?

That's not the theory of evolution. That's a question of taxonomy and demarcation. It's a real problem, but mostly with the way we typically think about such things, as oppose to the reality of evolution. Evolution doesn't directly deal with speciation, or how far is far enough to say that one species stops and another species starts. That's like asking where childhood ends and adulthood begins. There's just not a clear point.

Evolution says that the struggle for existence and nature selecting such that the most advantaged individuals have the most children who are similarly advantaged. This ensures that species tend to adapt better to whatever niche (way of living, food etc) they occupy. Evolution says that species adapt to changing conditions of life, and can result in amazing adaptations and solutions to environmental problems. This is all evolution says. Things go forward. But since they go forward in different ways, they also tend to drift apart.

Where the species fork, and part irrevocably is a matter of happenstance and saying how far is far enough, and what a species is, turns out to be a harder problem than one would suppose because gene pools in populations do not adhere to the sort of Platonic ideals. There is no perfect human. There's no absolute ape. There's no abstract rabbit to which all rabbitness is to be compared. That's just not the way it works.

If you go child, to mother, to grandmother, to great grandmother, and so forth and go back 350,000 generations, you'll never hit a point where a child was a different species than it's mother. It just doesn't happen. However, if you do this, with me and you do this with Oliver the Chimpanzee you'll end up at the same critter. My 350,000th grandmother is likely the same as his 350,000th grandmother. And at no point were any of my ancestors a different species than their direct offspring. And at no point were any of his ancestors a different species than their direct offspring. But, at some point, at some time, you could draw a line and say that these distant cousins are now two different species. But, that line would always be arbitrary.

We think there's some absolute human, that somehow adheres to a Platonic ideal of humanness. But, really that's not how things work. I mean, would one consider Neandertals a different species than human beings? They broke off the main human lines some 600,000 years ago. But, it turns out that modern humans interbred with them, and anybody with European ancestry is like 3% Neandertal. So are they really human? Were they always human? The Denisova hominims broke off of the Neandertal stock, and share a common ancestry with homo sapiens some 600,000 years ago too. But, they too interbred with humans in modern Melanesians (people in Oceania, like Vanatu where you get black-skinned kids with blond hair likely due to such influence). And apparently Denisova also from time to time (if a newly found toe bone is to be believed) bred with their closer cousins the Neandertals. So were any of these really different species? Under different definitions there are different answers, because the term species is absolute and evolution is gradual and progressive.

Species in some sense are a sort of hind sight thing. It is certain that at one time all of the rodents and all of the lagomorphs (rabbits, hares, pikas) had a last common ancestor (which DNA analysis suggests lived ~90.1 million years ago). This last common ancestor had at least two offspring. One of which gave rise to all the mice, rats, capybara, beavers, squirrels, porcupines, etc, and the other which gave rise to every rabbit, hare, and pika. Somewhere along the line, you can draw a line, but it would an arbitrary line. And is somewhat irrelevant to the actual history that actually happened with regard to their populations. And more and more this is what we're finding. Taxonomy is largely what we tend to call things, we give populations names. But they aren't that exact thing, there is no exact thing. They gradually change all the time.

This is largely why more and more we're trying to move away from such things. Replacing the typical system of taxonomy with a nested hierarchy so we can say that this last common ancestor of rodents and lagomorphs was a glires and so are all of its offspring. But, this ancestor doesn't necessarily fit into any of the subgroups of it's progeny.

So if for example in the distant future, many animals have died off, and bats have diversified to take over their now open niches. Let's say there are bats that swarm during the day, bats that swim under the ocean, bats the size of mosquitoes that suck blood from bats that that graze in the fields. All of these bats would be different species, but they would never stop being bats. There would be more groups inside the old groups, but the old groups, which would be the species we currently know, wouldn't stop being real. Perhaps the bats under the ocean and the bats that graze in the fields, and the ones that burrow into trees to hunt for insects, would all be fruit bats. So fruit bats wouldn't be a species but rather a group of distinct species (to some extent they are as there's many species of fruit bats), just as the glires are a group that gave rise to every rabbit and rodent on the planet.

Which is a long way around to the question you initially asked. Largely this creationist is confused as to what evolution says and what problems are really problems for the theory. The problem here is with our old ideas of taxonomy and what species are. This isn't a problem for evolution. Reality is what reality is. Our taxonomy needs to fit with reality rather than our general beliefs about names and putting things in boxes (Platonic ideals). It's all gradual, and there are no absolute lines, and we know this because we know evolution. It isn't that there's flaws in evolution, it's that there are flaws in the way we think about biology and evolution lays these errors out for us.

How in layman's terms did the first humans evolve from apes and then proceed to separate themselves from the apes?
It doesn't work like that. We didn't separate ourselves from the apes.  At some point some of our ancestors took different paths than their siblings. One brother went one way, and the other brother went the other way, and they never got back together. And these ancestors of ours were apes, so we are apes. We don't ever stop being apes. Populations split and divide. The group that gave rise to the orangutans went one way and the group that gave rise to the gorillas/humans/chimps/bonobos went another and didn't get back together. Then the group that gave rise to the mountain and lowland gorillas went one way and the group that gave rise to the humans/chimps/bonobos went the other, and didn't get back together. And the group that gave rise to humans went one way and chimps/bonobos went the other. And then the chimps went one way and the bonobos went the other. There isn't some set in stone principle that says this is X and it perfectly exemplifies Xness. There are populations and they divide. Sometimes they get back together and sometimes they don't. When things started, they were no different than one brother is from another brother, in fact, necessarily you could find a set of siblings that gave rise to every divided group. You could find a pair of siblings where one gave rise to all the reptiles, dinosaurs, and birds, and the other to all the mammals.

At what point did breeding with apes stop by humans?
 There's no absolute lines there. Humans are apes. And humans breed with humans. So in a very real sense humans still breed with apes (namely humans). But, looking back to our last common ancestor with chimpanzees (our closest relatives), and it may well be that humans might still be able to breed with them! It's not impossible for lions and tigers to breed or horses and donkeys. They produce offspring, and it might well be possible to have human-chimp hybrids. We just don't try it. So at one point did the ancestors of all humans and the ancestors of all chimpanzees stop breeding? -- They stopped breeding when they stopped. Seemingly about 7.8 million years ago or so.

There are some humans in some distant parts of the rain forest who do not know civilization. The large interbreeding population of humans haven't bred with them since we stopped breeding with them. If for some reason we never started back up, eventually we couldn't and we may well end up with two species of humans, such as the Morlocks and the Eloy (from H.G. Well's the Time Machine). It all depends on when the populations stop and happen to stay stopped.

So how did we separate from the other groups of apes. We went one way, and the other group went another. At what point did we stop breeding with them? We didn't breed with them anymore, when we didn't breed with them anymore.

The actual answers seem sort of anticlimactic, and they are. But, mostly because the problems are with our understanding and not evolutionary theory. We tend to see species as these distinct things which fit into these specific boxes. But, that's not what they are. They are siblings and a few million years of isolation. If you want to draw a line, at some point and say your 30,000th cousin is no longer the same species, you can, but realize that it's an arbitrary line, and our 30,000ths cousins the Neandertals bred with us just fine.
You could go further back, but it's still all just where you draw the line and that has nothing to do with evolution, that has to do with you and your line.

" The other day I saw a post from a creationist stating that the Theory of Evolution has to have some fault in it because there is no interbreeding of species."
No. There's a problem there but it's our idea of species that has the fault, not the theory of evolution.


Kay said...

THAT was sweet. Thank you. I'll probably be back later to comment further.

Wondering how you see nature evolving towards the future. Have you ever thought about it?

Kay said...

I mean *SWEEET

Tatarize said...

Depends a bit on how much of it humans kill before flaring out. We're going through/causing a rather shocking extinction event. Making more of the same off the table for a good chunk.

Kay said...

How can this be considered a part of Natural Selection?

I have more questions, but I saw your reply and came up with another.

Kay said...

Fascinating, and I think it has finally *clicked* with me.

After re-reading, I really don't have anymore questions for now; however, Xness? lol. Never heard of it before.

Tatarize said...

Xness, the quality or capacity of being X. Where X is a variable rather than an actual thing. Like Rabbitness is the quality of being a rabbit. Though, if you look back things gradually change and you're stuck trying to decide what is a rabbit and what is a proto-rabbit and it doesn't really matter because that's just about what you call things.

Tatarize said...

One species driving a large amount of the species on the planet extinct has a lot to say about the evolution and the future.

After most of the dinosaurs were killed off (by an impact), a huge swath of mammals started filling the now vacant niches. There were sloths the size of cars, and giant armadillos and bunches of really freakish things. I say freakish because they didn't survive to the present day. Had they, they'd just be critters. Driving as many critters extinct as we have, there may well be a lot of room. For lots of interesting stuff after people.

Kay said...

Thanks Tatarize. Would you be interested in writing another blog in regards to the following comment you made?

Tatarize said, "Depends a bit on how much of it humans kill before flaring out. We're going through/causing a rather shocking extinction event. Making more of the same off the table for a good chunk."

Tatarize said...

"Depends a bit on how much of it humans kill before flaring out. We're going through/causing a rather shocking extinction event. Making more of the same off the table for a good chunk."

The future of biology on this planet pivots heavily on how humans die-out and how much of it we kill. Normally one would predict more of the same, because that's typically a pretty good guess. But, with the mass extinction going on presently, that is not the right answer. So really I don't know what the future will hold. I haven't the foggiest idea.