Re: Hard science of evolution


<geoproc@xxxxxxxxxxx> wrote in message news:1186496797.481772.181440@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Occasionally Bimms makes the claim that evolution is not a rigorous
mathematical subject like, for example, physics, for which every
principle has a cool equation with squares and divides and stuff. I of
course have never believed him on this, since creationists are well
known for making pronouncements about the theory of evolution without
actually having looked at it. Nonetheless, I myself could not point to
any mathematics either. So just out of curiosity, I looked up
population genetics on wikipedia and was immediately confronted with
statistical equations and models of exactly the kind Bimms claims is
lacking.

What I want to know is, why isn't any of this stuff ever mentioned
much when people ask for the hard science behind evolution?

Well, one reason is that people's eyes glaze over when you show them the
math. Or they assume you are just trying to snow them. Or, if they are
really good, they look at the math carefully and notice the unrealistic
assumptions embedded therein.

All mathematical sciences involve unrealistic assumptions at some level.
Just think of the frictionless sliding blocks and unstretchable cables
running through inertia-less pulleys that you encounter in Physics 101.
Of course, they are there just to simplify the math. People don't object
too much, but that is partly because they are not working under a religiously
inspired agenda of discrediting the whole program of Newtonian mechanics.

But, as it happens, the unrealistic assumptions embedded in the basic
population genetics math are often far worse than those encountered in
elementary physics. One reason is because the math is far uglier than
that in physics to begin with - so if you put in very much realism, no one
can understand the math.

Another reason deals with problems of measurement. Physics is very much
an empirical science - you can measure the starting conditions, run the
experiment, measure the results, compare to theory, and determine whether
or not all is well with theory and experimental setup. But measurement,
in the evolutionary theory part of population genetics, is far more difficult,
and sometimes practically impossible. One good example is the heritability
coefficient for fitness. The concept is at the very heart of the idea
of evolution by natural selection. If you survive better and have more
children than your peers, then your children should inherit that special
something from you so that they too can survive better and have more children
than their peers. And, if the theory is true, then it ought to be possible
to show this - to measure it. Observe a natural population carefully over
two or more generations, keep careful records of survival and reproduction
and good genealogical charts. And show that fitness really is heritable.
But there are problems with this. Beyond the obvious one of knowing what
the survival rates would have been for the children of the first-generation
population that did not survive!

Everytime anyone has tried to measure the heritability of fitness in the
field (i.e. not in a lab population of flies or bacteria) they have failed
to measure any. Heritability of fitness seems to be pretty small. Less
than about 0.04 anyways. So you would need to make very precise measurements
to be certain that it is positive. Suppose you set out to show that it is
definitely greater than 0.005, say. In wild elephants. Well, it happens that
there are probably not enough wild elephants in the world to achieve this
level of precision with any statistical significance. Not unless you continued
the observations for more than a few dozen elephant generations. Maybe you
should try birds. Ah! But it is difficult to be sure of paternity in birds
unless you get genetic samples from every bird that dies. But some of them
will be eaten by hawks before you can get the sample. And some will just fly
off to somewhere where you don't have observers stationed.

I've
always wanted to know if there was mathematics that can be used to
model evolution, and it seems this is it (although I failed to notice
before because in theory, population genetics is merely the study of
populations rather than evolution). Is it because it's so difficult
and specialised that most people don't know it, or maybe because
creationists don't ask very hard questions? It seems that the subject
of evolution would appear much more respectable and, as oxymoronic as
it sounds, real, if it looked like it was something people can
actually study.

Some creationists - ReMine comes to mind - are somewhat familiar with the
population genetics equations. But that doesn't stop them from doubting.
And if you look carefully at what Bimms is saying, you will see that he
is really objecting to the non-deterministic nature of mutation rather than
the non-deterministic nature of selection. And to things like the neutral
theory of Kimura and Nei which bring non-determinism to the forefront -
regardless of how impressive the math looks.

So, the bottom line is that while some pretty fancy and pretty useful math
exists, it doesn't suffice to impress the creationists. Nor is it meant to.
The fact that evolution happened is shown by a variety of observations
having little to do with the mathematical theory as to *how* it happens.
And the math showing *how* it happens does not (and maybe can not) make much
empirical contact with field experiments. It is beginning to make some contact
with sequenced samples of population genomes, but there are still enough
unrealistic and/or uncheckable assumptions so that we are still not in the
realm of hard science.

.

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