[Taxacom] Evolutionary misconceptions (was: Ladderisingphylogenetic trees)

[Curtis Clark]

On 3/10/2010 9:46 PM, Richard Pyle wrote:

> 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**.

None of us were there. We have the pregnant female's great^10 
grandchildren, and the mainland individuals. They are distinct 
morphologically, and are reproductively isolated. *Something* happened 
to lead to that (can you say "speciation"?).

The birth of that pregnant female's male offspring was the cladogenesis. 
*But only in retrospect*.

When I lectured about peripatric speciation, I pointed out that on the 
periphery of many species there are multiple oddball isolated 
populations, most of which either fail or re-establish gene flow with 
the bulk of the species. Only rarely will one of them persist to become 
a new species (many are called, few are chosen). The rest are noise. 
*But only in retrospect*.

As self-aware results of sexual reproduction, we tend to think in 
absolutes about lineages--"I" started with an act of syngamy, which in 
one step differentiated me from both my parents. But how early does a 
miscarriage have to happen before it wasn't a separate person (the 
foundation of much of the abortion debate)? Again, the answers are much 
clearer in retrospect.

One of the Aristotelean conceits that continues in modern biology is the 
premise that archetypes are timeless. Because the reality of a species 
would not be apparent to any observer possessed of all the facts that 
exist at any given time, gosh, they must not be real. The physicists 
gave up that conceit a while ago. I'm not sure they even care whether 
those hadrons and baryons are "real": they allow prediction, 
reproducibility, and hypothesis-testing to occur, and that's all a 
scientist can really ask for.

One can study, *in retrospect* (in most cases), the factors and often 
the events that lead to the formation of new "species", thus 
"speciation". These studies often allow prediction, reproducibility, and 
hypothesis-testing to occur. To say that species aren't real doesn't 
detract from that any more than saying that baryons aren't real.

But our training as scientists teaches us to eschew mixing science with 
mysticism. And so we resist the idea that we are studying something that 
is "not real", no matter how well it allows prediction, reproducibility, 
and hypothesis-testing. And we all know how dismissive it can be to say 
that a phenomenon is "not real".

So, for me, the bottom line is that species are real enough for 
scientific inquiry, and that's good enough for me.

-- 
Curtis Clark                  http://www.csupomona.edu/~jcclark/
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