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Originally Posted by Fred
I'm not terribly clear what you mean by 'effectively random . . . with respect to their effect upon organisms,' but if you simply mean that 'mutation' is random . . .'
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No, that is not what I meant . . . I would agree with you in abstract that, technically (in the sense that everything is determined, etc. etc.), mutations are 'non-random'. We could in principle predict which/when/where mutations would happen if we knew the exact state of every particle in the universe and were able to model their future dynamics (in practice, of course, this kind of predictive power is beyond reach).
What I really meant by "random" is that mutations occur without regard for their effect upon the adaptive design of organisms (with a few exceptions that prove the rule, but I won't go into them). In other words, mutational processes that inherently benefit organisms don't exist, and most mutations decrease an organism's ability to produce offspring. You could also think of mutation as a process that continually pushes populations toward higher entropy . . . without a complementary process that reduced entropy locally, mutation would result in lower and lower organismal fitness until the population crashed to extinction. This is one of the primary concerns with respect to very small, endangered species, in which selection cannot act strongly enough to combat mutational meltdown.
Natural selection is the complementary process that siphons and preserves order from a pool of mutational disorder . . . organisms that are best adapted to their environments preferentially contribute to subsequent generations, while less effectively-adapted organisms fail to contirbute or contribute less heritable information to subsequent generations (as you may intuit, the difference between the conitrbutions of more-fit and less-fit organisms is directly related to the strength of selection, as described by the mathematics of evolutionary genetics). Deleterious mutations are thus expunged from the population . . . to what extent this occurs depends upon the strength of selection, population size, mutation rate, reproductive mechanism of the species in question (sexual, asexual, etc.) and, in some contexts, immigration/emmigration rates. The details of why certain organisms and traits are more or less "fit" are highly context-dependent; e.g. a lizard that specializes upon swimming and consuming seaweed can do very well in a marine tidal habitat, but the same lizard is pretty screwed in a desert.
So, to re-iterate my meaning: mutations may in principle be governed by deterministic laws, but they don't preferentially benefit organisms or rain down according to a grand design. Rather, mutation is the process that drives populations toward the thermodynamic equivalent of entropy, and natural selection is the process that ultimately resists localized entropy (while allowing universal entropy to increase by the release of metabolic heat, etc.)