I've spoken on the naturalistic fallacy before but I recently came across a slightly more insidious variety, which doesn't have the same red flags as the fallacy in the forms it's usually encountered, such as revering nature because it's old, or pure, in ways which have no scientific basis. There's simply no good reason to believe that killing a wild turkey is healthier, or more nutritional, than a farm-raised turkey simply because the wild turkey is closer to nature. Perhaps it is, but the data would be found within the nutritional data for the turkey (less fat, perhaps, or more muscle definition) but not simply because the wild turkey is the natural one; it could also be riddled with parasites for the same reason. Natural becomes a non-issue, because we need to look at the specific traits belonging to that turkey, or that group of turkeys.
That aside, the fallacy I've been running into basically this: Trait X evolved, therefore it's beneficial. For instance, gender roles. I heard a brief argument recently that said that we needed to protect gender roles because they had evolved for a reason. To which my response was a resounding "Maybe."
The idea that something has evolved, therefore it is good, is patently false. Violence has evolved. That something has evolved and stuck around is simply a testament to one thing; it makes the bearers of those traits have more babies. In a world where tendencies toward violence were adaptive, violence was selected for. That world may or may not still be around. Evolution doesn't produce the best product; it produces the best compromise between effective and cheap, which is why men have nipples, we still hiccough, and very few of us are 8 feet tall.
Regarding gender roles, evolution almost certainly wasn't a factor, at least as far as strictly genetic evolution. A desire to wear dresses is not a chromosomal trait; it's a cultural one. And cultural norms change much more rapidly than genetic ones. Irrespective of that, though, the premise of the argument belies a misunderstanding of evolutionary theory, and is logically incoherent. Perhaps there are good reasons for gender roles; I doubt it. I think that as a society we've grown to the point where conformity isn't required, but that's the wrong reason to argue for it. Just as I mentioned in my blog on Climate Change, the reasons we believe something are important. It would be false for me to claim that one hot summer is good evidence for Climate Change, even if I'm right and Climate Change is occurring.
Evolution is a pervasive, powerful force, and understanding it is critical to understanding ourselves, biologically and socially. What it isn't is an excuse for bad behavior. It may explain an origin (and in the case of gender roles, badly at best), but it doesn't address the concern of whether or not the behavior is something we should encourage, and thus has almost zero weight as evidence for any cultural behavior. Deifying evolution as a basis for social actions is the naturalistic fallacy pure and simple, only masquerading as enlightened.