dabs

I didn't say "its all a mutation bias", you did. I said "dual causation". The "dual" in this phrase refers to the concept of "two", and the "causation" part refers to causation. The two kinds of causes are biases in the introduction of variants that did not exist previously (mutation bias), and biases in the reproduction of variants once they exist (selection). Got it?

Foodchain, your sentences are nearly incomprehensible, so its hard to tell what you are saying. It might help to run your draft message through a grammar-checker. In any case, it is simply wrong to suggest that natural selection determines what happens in evolution, which is how I interpret your claim that "the overall decision of what lingers and what does not in time is natural selection." Natural selection only "decides" between alternatives, but the alternatives must emerge first by mutation and development. Since the mutation rates are not all the same, this dependence on mutation can impose a bias on evolution. To explain how this works, let me repeat a metaphor that Stoltzfus used at a scientific meeting last summer. To understand what he calls "dual causation", he asked the audience to imagine a climbing robot, placed on a rugged mountain. The climber operates by a two-stage proposal-and-acceptance algorithm. In the first stage, the climber reaches out with a foot or hand to find a hold. This might happen multiple times before the second "acceptance" step, when the climber commits to the hold and moves his body. If the "acceptance" step is biased so that the climber is more likely to commit to a hand-hold that is higher (relative to one that is lower), then the climber will climb. That's like the effect of natural selection. It biases evolution to go up in fitness. But what if there is also a bias in the proposal step? What if the climber's left arm is more active and tries out more hand-holds? Then obviously, the climber is going to climb to the left. One can't insist that the acceptance step (i.e., the analog of natural selection) determines the outcome, because obviously it doesn't determine the leftward bias. The leftward direction is caused by the bias in the proposal step, and the upward bias is caused by the bias in the acceptance step. The key to dual causation is that both biases can happen at the same time (up and to the left), and they have separable causes.

Foodchain, the issue with mutationism is not what happens if we try to "subtract natural selection from the equation" of evolution, but what happens if we control for, or account for, effects of differential reproduction (fitness differences) and then ask "what is left?". Is there anything else, any pattern or phenomenology, that is explained, not by selection, but by differential effects of mutation and development? By analogy, we could ask (in the context of the nature-nurture debate), what happens if we subtract out the effects of genetic variance on some human behavior, e.g., violence? Is there anything left to explain? It is crucial to understand that, by asking this question, we are not saying that genetics can be removed from the mechanism that generates humans and their behavior. However, we *are* assuming that we have experimental and mathematical tools to separate out genetic effects from other effects when we are accounting for patterns of behavior. Indeed, these tools exist. One relevant tool in this case is the study of identical twins raised apart-- same genetics, different environment (same "nature", different "nurture")-- but its not strictly necessary to do it this way. And of course, the answer is that yes, when we subtract out the effect of genetic variation, we still have much to explain about behavior. There are environmental components to behavior. Obviously both mutation and selection are necessary in any account of the mechanism of evolution. The historical position of mutationists is not a position of neutralism, of denying selection. The position of mutationists is that both steps influence the outcome of evolution in important ways. By contrast, the neo-Darwinian position is analogous to genetic determinism, i.e., denying the relevance of one factor. The neo-Darwinians say that, although mutation is necessary for evolution to occur, the nature of mutation does not have any influence on *how* evolution occurs, what direction it takes, etc. Instead, the neo-Darwinian view is that "selection is the ultimate source of explanation in biology". Of course if you re-define "natural selection" in a broad and fuzzy way so that it ends up meaning "whatever happens in evolution", then of course "natural selection" swallows up everything, including directional effects of mutation biases.