[ExI] Is Evolution Random?
citta437 at aol.com
citta437 at aol.com
Thu Dec 6 19:52:13 UTC 2007
Random Relative to What?
To understand the randomness claimed for evolution by scientists, as
opposed to that feared by theologians and moral philosophers, it's
important to ask "random relative to what?" In any model of a process
as described by a scientific theory, there are many things taken for
granted. Philosophers of science refer to these as ancillary
assumptions or hypotheses. Some of these are assumed from ignorance:
science might not yet have any workable and tested theory or model to
deal with that class of phenomena. Others are assumed because they are
well worked out in another scientific theory or discipline.
For example, Darwin knew that there was heredity, but he did not have a
good theory of heredity to work by. His selection theory (the version
he and Wallace published) had to assume that traits were heritable. He
did propose a theory of heredity (pangenesis) based on a now
discredited view of the influence of the use of traits on reproduction,
but it was never essential to the theory of natural selection. So far
as his theory of evolution by selection was concerned, heredity was an
area to be filled out later.
Once Mendel's principles of heredity were rediscovered, permitting
mathematical models of genetic change at the level of populations to be
formulated by Haldane, Fisher and Wright and others in the 1930s and
1940s, the so-called Neo-Darwinian ("synthetic") theory of natural
selection used these results as ancillary hypotheses. Added to this
Weissman's germ plasm theory that the sex cells (the "germ plasm") were
not "reverse programmed' by the phenotypic organism (the "soma"), and
natural selection of genetic content became a one-way causal process.
Genes cause the ecologically active phenotype, but the phenotype does
not program the information content of the genes. Hence, relative to
natural selection, genetic content changes are "random". Let's call
this the Black Box Conception of Randomness [See Bowler 1983 on the
history of post-Darwinian theory and Dawkins 1996 for a fuller
development of this.]
Another way to say this is just that the changes that get encoded in
genes occur with no forethought to the eventual needs of the organism
(or the species) that carries those genes. A gene change (for instance,
a point mutation -- a mistake at a single locus of the genetic
structure) may change in any way permitted by the laws of molecular
biology, according to the specific causes at the time. This may result
in a phenotypic change that may be better suited to current conditions
than the others about at the time. However, it probably won't. So far
as the local environment is concerned, the change is the result of a
random process, a black box that isn't driven with reference to things
going on at the level of the environment. It's not really random, of
course, because it is the result of causal processes, but so far as
natural selection is concerned, it may as well be."
Is it safe to say then that Evolution can both be random in some ways
as in genetic mutation and deterministic in the molecular level?
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