[Taxacom] Evolutionary misconceptions (mother-daughter pairs)

[Richard Pyle]

Curtis wrote:

> I 
> was referring to an ancestral species totally transforming 
> into a descendant species without lineage-splitting, which 
> IMO never happens.

So let me make sure I understand you correctly.  Using Ken's
pregnant-female-on-an-island-example, let's take the premise that the
great^10 grand children of the pregnant female have diverged in form and
genome from the original mainland population sufficiently enough that all
taxonomists on the planet agree they are distinct species. I'm assuming we
agree that when the pregnant female arrived at the island she was the same
species as the original mainland population, and that the speciation process
occurred over the course of the great^10 generations.

Scenario 1:
Just as Ken described it -- after great^10 generations, we've got two extant
species -- the one on the island, and the original ("ancestral") population
on the mainland.  Are we in agreement that this is a clear-cut example of a
linage split resulting in speciation?

Scenario 2:
Soon after the pregnant female arrived at the island (before her descendants
had diverged from the original population), there was a major environmental
event that wiped out the original population, but left the pregnant female's
population intact.  There is a rich fossil record for the original
population.

Scenario 3:
Same as scenario 2, except no fossil record.

Scenario 4:
Same as scenario 2, except the extinction of the original population was
caused by humans in recent times, well after the great^10 generations of the
insular population had diverged from the parent population.

My question: Did speciation happen on the island in all four scenarios?

If you answer yes, then it seems to me that you can't escape the fact that
the pregnant mother was a member of an ancestral species that totally
transformed into a descendant species (on the island), without lineage
splitting.  If you want to say that lineage splitting happened prior to the
transformation process, and was therefore necessary for the speciation to
occur, then what if the pregnant female was not geographically isolated from
the original population, but was rather the only survivor of the extinction
event? Does a population bottleneck count as a lineage split (with only one
continuing branch)?

If you don't like the extreme example of a single pregnant female, then
replace all of the scenarios with a large population that was cut in half by
some major vicariant event (e.g., closing of the isthmus of Panama), with
the same four scenarios.

If, on the other hand, your answer to my first question is "no", then I'd
like to know which of the scenarios counts as speciation, and which doesn't.
And why.

Maybe I completely misunderstand what you mean when you say "an ancestral
species totally transforming into a descendant species without
lineage-splitting ... never happens".  But by my reckoning, *every* species
is the product of a sequence of reproductive events in which an ancestral
species transforms into a descendant species -- whether or not any of the
siblings or cousins happened to persist long enough to exist today or be
represented in the fossil record.

Aloha,
Rich