Re: The Paradox of Speciation

On Dec 1, 8:11 pm, treusd...@xxxxxxxxx wrote:
_Arthur wrote:
On Dec 1, 10:28 pm, treusd...@xxxxxxxxx wrote:
Sorry, no. Small changes that don't significantly reduce reproductive
compatibility can build up over time into big changes that do.

And when the big change finally manifests itself, it will be selected
against in favor of reproductive continuity.

How ? If the 2 populations are separated one from the other, say one
is on an island that is cut from the continent, how are they supposed
to maintain, favor or select "reproductive continuity" ?

Support your assertion.

The separation of an original big population into two smaller ones is
irrelevant. The two populations were the same species at that moment
and remain so. The founders of the offshoot become the new reference
group. It doesn't matter if there were more like them elsewhere a long
time ago.

You seem to be missing the basic point that there is no reproductive
advantage to retaining an ability to mate with members of the
population with whom you will never come into contact.

Let's look at a hypothetical example. A few birds of species A are
carried by an unusual storm to a remote island which previously had no
birds of that species. Back on the mainland the birds of species A
had developed some particularly bright and distinctive coloration
which was positively selected because it helped them find compatible
mates among the plentiful varieties of bird species found there with
otherwise similar appearance. But in the new environment on the
remote island the distinctive coloration has the main effect of making
the birds easy to spot by a predator species while no longer providing
the advantage of finding mates since there are no similar bird species
present in the new environment.

Now birds in the new island environment that happen to have less
pronounced coloration will be less subject to predation while still
being able to find mates and this trait will eventually become fixed
in the population on the island. Eventually the coloration may be
lost entirely and any birds from the island population that happen to
be blown by another storm to the mainland are no longer recognized by
the birds there as belonging to the same species and therefore no
longer mate with them (and there may well be other changes that have
happened in the intervening generations that also prevent successful
mating).

At this point the island population of birds would be recognized as a
new species and will continue to develop separately from the mainland
population *even if* changing weather patterns or other physical
changes bring them into more frequent contact.

.

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