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"Random selection": an oxymoron.




On Sun, 24 Jan 1999 Dinogeorge@aol.com wrote:

> New species appear randomly, or what is effectively the same thing,
> unpredictably, because the events that produce new species are contingent on a
> huge number of variables. Certainly the organisms in a daughter species will
> resemble the parent organisms, but >how< they will differ, or >whether< a new
> species will appear at all, is unknowable in advance.

By us, now.  But trying to perceive patterns in apparent disorder is one
of the most beautiful things in science, Man.  
 
> You may imagine you have identified a trend or a rule or a tendency of
> evolution, but such rules are much like loading dice--one may increase the
> odds that certain combinations will be thrown, but for any particular throw
> one still can't be sure of the outcome. This is the nature of natural
> selection.

Here is a simple example.  On a tree covered with lichen a white peppered
moth will be taken at a lower rate than the dark moth.  This is a rule we
have identified.  And with regard to moths and their predators it is
pretty iron clad.  Now, throw in a variable. See if I can make a
prediction (after all, I could do the experiment).  Strip off the lichen.
Now the dark moths are harder to see and the population will evolve to
have a higher frequency of taht allele.  This is no random change.  It is
_selection_.

> This is also, for example, the essence of something like Cope's
> rule for tetrapods. There seem to be more selection pressures to evolve larger
> size than smaller size, but every so often things work out such that a smaller
> organism evolves from a larger one; and most often there is no significant
> size change one way or another.

No.  This Cope is a rule akin to the medieval belief that the Sun went
around the Earth.  The appearance disguises the true underlying causes.  
Of the roughly 10,000 bird species, most 
are small and are staying that way.  Why? Because, as Collias says, being
small and flying allows them to conceal their nests.  This is a valuable
rule.  Well, let's see what happens if we relax the predation pressure by
putting a small species on a predator-less island.  Pressure keeping them
small disappears making other selection processes more important.  Another
rule says: Due to Size/Metabolism economy of scale, it pays species to be
bigger (until pathologies of size or some other competing force kicks in).
These rules (and I am really not saying they are true--but they do deserve
attention to figure out if they are true) are much more useful and
predictable than the simplistic: Species grow bigger.

> If there's any true or obvious "trend" or
> "rule" in evolution, it must simply be evolutionary stasis from generation to
> generation.

As I noted before, this is Hardy/Weinberg land.  And this condition only
holds if there is no natural selection, no mutation, no genetic drift, no
gene flow, random mating--which is to say: NEVER!!!

> Lots of scenarios have been advanced over the years to account for the
> differential survival of one species (particularly _Homo sapiens_!) over
> another, but there is really no way to confirm whether any of those scenarios
> holds water. Some sound quite plausible, others do not. We need to observe
> populations of organisms in detail for periods of time measured in hundreds of
> thousands of years to see whether evolution really does take place according
> to the scenarios we have put forth, and whether new species do indeed appear.

So let's start watching.  Perhaps we will find there really is more to it
than luck.