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I have a couple of things I don't understand about the Neaderthal interbreeding and the Denisovan stuff: (1) If we interbred, doesn't that mean we're the same

by netcan 12y ago

I have a couple of things I don't understand about the Neaderthal interbreeding and the Denisovan stuff: (1) If we interbred, doesn't that mean we're the same species. IE, These were two subspecies like dogs and wolves. (2) How does the idea of distinct human populations without Neanderthal DNA work with the genetic bottleneck theory? Wasn't there a bottleneck after this interbreeding took place>

ajuc 12y ago
Species are artifical divisions, nature isn't that strict. If species worked 100% of the time there would be no evolution. Horses and donkeys can interbreed, tigers and leopards too, and there are more examples, sometimes the ofsprings can breed too. Almost all rules in biology should have "except when not" added.
Amezarak 12y ago
I think of it like this: there's not really any such thing as a "species" in nature. It's an abstraction we developed to make sense of the world. In reality, organisms exist on a huge continuum composed of individuals which are more or less genetically similar/related. Often there are huge "chunks" missing where lines died out or went their separate ways. We arbitrarily declare that such-and-such collection of organisms between this point and that point on the continuum are a distinct species. Sometimes, this species can interbreed with another and even have fertile offspring, but they just don't - even if they live in the same locale! Sometimes two species are even more genetically similar than the first example, but they can't interbreed at all. Sometimes two organisms could interbreed, but it's physically impossible for some reason (very small dogs and very large dogs) without some kind of assistance. Sometimes they can, but the offspring is not fertile. And as you get further and further away on the continuum, the less likely they can interbreed at all. In nature there's really all kinds of different scenarios like these and it doesn't necessarily make sense to demarcate the species-line where we do - but it was done that way for historical reasons or simply because that's the best we can do with our abstraction.
bpodgursky 12y ago
Inter-breeding success isn't always all-or-none. A lot of the time you'll get sterile or un-viable offspring when the species are on the brink of incompatibility. So the fact that it was successful some of the time (which is clear now) doesn't necessarily mean most offspring survived.

by netcan 12y ago

ajuc 12y ago

Species are artifical divisions, nature isn't that strict. If species worked 100% of the time there would be no evolution. Horses and donkeys can interbreed, tigers and leopards too, and there are more examples, sometimes the ofsprings can breed too. Almost all rules in biology should have "except when not" added.

Amezarak 12y ago

I think of it like this: there's not really any such thing as a "species" in nature. It's an abstraction we developed to make sense of the world. In reality, organisms exist on a huge continuum composed of individuals which are more or less genetically similar/related. Often there are huge "chunks" missing where lines died out or went their separate ways. We arbitrarily declare that such-and-such collection of organisms between this point and that point on the continuum are a distinct species. Sometimes, this species can interbreed with another and even have fertile offspring, but they just don't - even if they live in the same locale! Sometimes two species are even more genetically similar than the first example, but they can't interbreed at all. Sometimes two organisms could interbreed, but it's physically impossible for some reason (very small dogs and very large dogs) without some kind of assistance. Sometimes they can, but the offspring is not fertile. And as you get further and further away on the continuum, the less likely they can interbreed at all. In nature there's really all kinds of different scenarios like these and it doesn't necessarily make sense to demarcate the species-line where we do - but it was done that way for historical reasons or simply because that's the best we can do with our abstraction.

bpodgursky 12y ago

Inter-breeding success isn't always all-or-none. A lot of the time you'll get sterile or un-viable offspring when the species are on the brink of incompatibility. So the fact that it was successful some of the time (which is clear now) doesn't necessarily mean most offspring survived.