Posted: Jun 15, 2017 1:11 pm
Thommo wrote:
Just because every generation may be able to interbreed with its predecessor and successor that does not mean it must be able to interbreed with its 99th degree predecessor or its 9999th. The intermediate generations have long since passed away, closing down the pathway through which genetic information once flowed in exactly the same way as geographical isolation.
Let's play along with this. So your argument is that interbreeding is possible for the immediate predecessors/successors but that if we go back 100 genertions or so, interbreeding might not be possible. OK. But in the gradual model you espouse, there has to be a point at which, if we did have the two generations separated by time living contemporaneously, interbreeding wouldn't work out. Thus, the parents of the offspring of generation Y might just about be able to interbreed with their ancestors of generation X, but the offspring, repesenting generation Z, might not be able to because a threshold has now been crossed and the cumulative number of incremental changes means a new species has now arisen.
No, because species is a concept relating to multiple populations alive at the same time. Borrowing that concept for a different situation doesn't directly translate like that.
Well, Homo erectus and Homo sapiens were contemporaries and yet the former was also ancestral to the latter.
It is. It is purely a matter of convention.
It is also a matter of definition in terms of reproductive compatibility.
Maybe, maybe not. Wouldn't matter either way in terms of a general principle though. If (as you repeatedly suggested) it's impossible for speciation to occur without such a quantum leap then you're about 4 billion examples short.
Well, at least in plants, whole genome duplications can easily result in a new species suddenly appearing as Dawkins admits. That isn't a quantum leap though.