[Taxacom] Evolutionary misconceptions (was: Ladderisingphylogenetic trees)

[Richard Pyle]

I've been quietly brooding as this thread goes on in the background.  There
have been many statements that I wanted to comment upon, but I know from
experience that doing so would only further exacerbate my
already-overflowing email inbox.

But Ken, you've given me a temptation to comment that I am finding it
difficult to resist.

>       But what really concerns me the most are very asymmetic 
> "splits", the most extreme occurence probably being a single 
> pregnant female being isolated in a new isolated habitat 
> (like an island).  The new population obviously will be just 
> a new subspecies until further anagenesis results
> in reproductive isolation which exceeds mere geographic 
> isolation.

I think I understand what your point is, and if I understand correctly, I
don't think I disagree.  But consider the scenario as you describe it in the
above paragraph.  I know this is not your point (this message is not
directed at you; it's directed at this whole exchange), but let me ask this:

When the preganant female arrives at the island, is it suddenly a new
species?  (please say 'no'...please say 'no'....please say 'no'...)

When it gives birth to its offspring on that island, is that offspring a
separate subspecies from its mother? (please say 'no'...please say
'no'....please say 'no'...)

What about when that (presumably male) offspring goes Oedipal and produces
more offspring with its mother, are those offspring a different subspecies
from their parent?

I'm going to guess (hope) that we are all in agreement that the answer to
all three questions above is "no".  And I know that's not what you were
implying.  But the reason I'm replying (something I'm sure I'll come to
regret), is to make a broader point.

We all seem to agree that eventually, with sufficient genetic isolation, the
descendants of that pregnant female will anagenize into something with
consistently different morphological traits/DNA sequences/reporductive
imperfections to the point that we would regard the members of that
descendant population as a distinct "subspecies" from the descendants of the
original population from which the pregnant female came. 

The point is (echoing what I've said many, many times before on this list),
that process from single pregnant female to descendant population that is
sufficiently divergent that we regard it as a distinct subspecies, happens
one reproductive event at a time. Unless you're willing to decalre that one
offspring was a distinct subspecies from its parent (second question above),
then the boundary between "same subspecies" and "different subspecies" is
necessarily fuzzy.

The easy counterpoint to this is that, looking at the larger picture, there
was a discrete event when an otherwise coherent population began its
divergence down two separate paths.  Thus, we can draw a nice little
cladogram and declare the node to be the founding pregnant female.  But this
counterpoint ignores the fact that the divergence process happens **one
reproductive event at a time**.  And besides, what happens when we step back
even further?  Now instead of looking at fuzzy boundaries between "same
subspecies" and "different subspecies", we're now talking about "different
subspecies" vs. "different species".  Back off a bit futher and we're
talking about "same subgenus" vs. "different subgenus" ... And so on and so
on. Once again, the process is extremely fuzzy -- happening **one
reproductive event at a time**.

So the argument between anagenesis vs. cladogenesis is, to me, essentially
the same as the "species are real entities in nature" vs. "taxa are a
convenient mechanism to communicate with each other about the heterogeny of
life on Earth" debate. In other words, it's an argument with no winners and
plenty of losers.

>       Likewise, I would not assume that all students 
> (especially college biology majors) have modern monkeys in 
> mind when they say that apes (and thus humans) evolved from 
> "monkeys".  Perhaps some of them just a have a more intuitive 
> understanding that mother-daughter species are just as 
> important to evolution as the less asymmetic sister-sister 
> splits that Hennig emphasized.  

Something to keep in mind here:  the only difference between a series of
mother-species/daughter-species, and an array of vicariantly fractioned
populations leading to distinct species, is that in the former case, the
descendants of the fractioned populations failed to persist long enough to
diverge/survice today/leave a fossil record.  In other words, the difference
isn't about the evolutionary path by which a given line of organisms came to
be what it is today vs. what its ancestors were eons ago; the difference is
in whether or not completely separate lines of organisms persisted or
failed.

Every organism on the planet got to be where it is today by exactly the same
fundamental process: ONE REPRODUCTIVE EVENT AT A TIME!

Aloha,
Rich

(Hmmmmm.....Delete key? Send key? ..... delete key? send key? .... Delete
key? Sen....  Oops...)