Re: The Paradox of Speciation

treusdrie@xxxxxxxxx wrote:


John Harshman wrote:


How do you explain mutations in A1 causing infertility with A2 while
not causing infertility within A1? At the same time these mutations
are being passed around in A1 to make it infertile with A2, the
members of A1 are loosing fertility among themselves by exacly the
same process.


If you follow the argument carefully, you will see that there is no time
at which any member of A1 is infertile with respect to any other member
of A1. The simple explanation for this is that genes interact. X and Y,
by themselves, may be harmless or advantageous, but the combination of X
and Y may be lethal. So if X is a mutation in A1 that becomes fixed in
A1 and Y is a mutation in A2 that becomes fixed in A2, it's good for
each population separately but bad for their reproductive compatibility.


Very good.

If A1 is compatible all the way back to A (the original, unified group
before separation), and A2 is also compatible back to A, then what we
is have is essentially some A with X and some A with Y. The situation
is the same as in your previous examples. Again, as before, I admit
that you have answered the problem, but only on a technicality that
does not apply to the underlying situation of life as observed. Surely
you're not claiming that all species on earth are still reproductively
compatible with a remote common ancestor. Your solution only works by
introducing a reproductive (not to say overall) defect that cannot
create the evolution of reproductively incompatible species down the
line of descent, but rather only on lateral branches which I have
already conceded as possible but of limited significance.

I have no idea what you imagine the difference to be between "the line
of descent" and "lateral branches". I have no idea why you think this
simple means of achieving incompatibility between descendants of a
single species is "a technicality that does not apply".

Of course I'm not claiming that all species are reproductively
compatible with a common ancestor. I've just given you a mechanism by
which this incompatibility can evolve. It's as easy to do it in a single
lineage as in two. The only difference is that X has to be the original
allele, which is lost (to some other allele) before Y comes along. And
of course in real species there are likely to be hundreds of such
alleles, with more coming into existence all the time.

.

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