Posted: Jun 15, 2017 11:51 am
Thommo wrote:
Umm, exactly. You have an arbitrary division (the number of digits in base 10, these numbers have the same number of digits in base 9 and 11) and you can get there with "parent numbers" that are no more different than any other set of "parents".
The point is that, at least in base 10, there is a difference between 99 and 100 which is more than just a small increment. The latter has three digits whereas the former only two. A threshold has been crossed even though it took 90 increments.
So to recap:
- You have agreed that there is no barrier to new species emerging (this is known as speciation).
- You have not challenged that large differences of any magnitude can accumulate by incremental small steps.
- You are still puzzled by the arbitrary way species get named and distinguished into categories historically.
All I am saying is that a new species can only emerge if the parents of one species give birth to offspring of another species at some point - or else the same species remains. There may well be a gradual process leading up to this, but the change has to occur if a new species is to arise. If we were to trace your ancestors far back enough, one of them would eventually not meet all of the criteria for being an anatomically modern human and so would have to be categorised as a different species. However, its immediate descendant would (just) be sufficiently modern to be part of our species, thereby refuting Dawkins.
The thing you're puzzled over doesn't matter though, it's purely conventional, and that convention is (roughly speaking) that we refer to ancestors of a population as being of a "different species" if their genome would not allow them to directly interbreed with the descendant population if both populations were alive today.
Got that. But it's not just a case of historical retrospection and interpretation. As I mentioned, the ancestor with the fused chromosomes, 2a and 2b, may have been reproductively isolate from its parents. The loss of the baculum (penile bone) could have happened within a single generation, and this could have caused issues with interbreeding.