It's taken me quite a few decades to clarify my understanding of evolution. Like many people, I once believed that evolution somehow improves a species. Problem is that we think of improvements from our human point of view. That often makes our notions of improvement irrelevant. And even when our notions of improvement are relevant, they may be mistaken.
A widespread mistaken expectation is that evolutionary theory gives definitive answers. It doesn't. No science does, although some answers are more definitive than others.
Several years ago, a blog I read claimed that the epicanthic fold is “unimportant” if not “useless”, and therefore its existence makes the theory of evolution doubtful. For evolution is all about developing useful traits, right?
Well, no, actually. I'll take up the epicanthic fold.
a) "Unimportant" and "important" aren't what a human might think they are. Just because someone may think something is an unimportant feature doesn't mean that it really is. What’s more, “important” depends on context. "Context" for an organism means its environment.
b) The epicanthic fold may be a consequence of genetic drift. Evolution will not eliminate neutral changes in the genome. Accidents of mating may therefore concentrate some part of a genome and so enhance a particular variation of some trait. The primary accident of mating that affects this is the size of the mating pool. In a small population, genetic drift can show up within half a dozen generations or less, and can disappear just as quickly. In larger populations the effect is slower. However, a trait may become universal. A secondary cause of genetic drift is aesthetic preferences (for want of a better term), aka as "sexual selection".
c) Actually, the epicanthic fold is helpful in the Arctic in late winter and early spring, when there's still lots of snow around, and the sun is higher in the sky. By shading the pupil of the eye, it reduces the glare from snow and sky. Fact is, the Inuit made sunglasses by cutting narrow slits in flat bones which were fastened in front of the eyes. These are artificial epicanthic folds taken to the extreme, so to speak. It’s also helpful in insulating the eye.
d) The epicanthic fold shows up in several variations. I have a version, but it's not like the one you would see on a Japanese person.
Generally speaking, the phrase "survival of the fittest" has caused much misunderstanding of evolution. It does not mean "survival of the strongest/fastest/etc". It means "survival of those who fit their environment best; those which are the best suited to their environment”. At the time the phrase was coined, “physically fit” was also becoming common. It meant something like “physically well put together, hence suited to strenuous exercise”, but quickly morphed into “physically superior”.
“Being best suited to their environment” has a consequence that may seem counterintuitive when evolution is seen as primarily explaining changes. Evolution will preserve traits necessary for life, or that maintain a good adaptation to the environment, even if the environment changes. That’s why we share so much of our genome with other animals. The shared bits code for features such as enzymes or hearts, without which survival would be impossible or difficult in any environment.
On the other hand, genetic changes can change the environment, because every organism is part of the environment from the point of view of the other organisms in that environment. If the change confers some survival advantage, there will be new selective pressures on some of the other organisms, and they may change, which may change the selective pressures on still other organisms, including the one that triggered the changes. That means that adaptation is a complicated feedback loop. Or rather a feedback tangle, which means it’s a complex system. As in ecosystem. Unfortunately, our brains are not very good at making sense of simple systems, let alone complicated ones.
As for genetic determinism: People who believe that genes rule are way behind the curve. Genes cannot "determine" anything in the absence of environmental inputs, which includes inputs from other components of the organism itself. In fact many genes will have no effect until some environmental trigger causes them to "express", that is, to start making the proteins they specify. What happens next may eventually trigger other genes. This, in a general way, is how an organisms grows an develops.
You are what you are because of your genes _and_ your environment, and your environment includes the environment of your ancestors. Environmental factors can change the DNA by a process called "methylation", which affects gene expression. One consequence of methylation is that a mother's illness can affect her children and grandchildren, and possibly even her great-grandchildren.
Evolution is complicated, but it works because of the interaction of the environment and genetic differences between individuals. If an individual lives long enough to reproduce, its genes and the genes of its mate will survive for another generation. If some variation improves the odds of having more offspring than average, that variation may spread through the following generations until it dominates the population. Cumulative changes may make offspring long separated in time and space so different that they are different species.
But what’s a species? That’s another concept that's not so easy to define. I’m not happy with my concept. I may discuss the results of my attempts at clarification here. Or maybe not.
No comments:
Post a Comment