For people who are interested in protecting the environment and living a healthy life it is easy to fall into a sort of trap. Huge amounts of damage can be done by doing things that are "unnatural": misusing synthetic (unnatural) chemicals, using unnatural drugs, introducing exotic (unnatural) species into new areas, or the wholesale replacement of the natural mix of plants and animals by huge monocultures of corn or wheat.
In fact, a fairly safe rule to follow is that if you leave something in its natural state, you're less likely to get into ecological trouble than if you change it. Since staying out of trouble is generally "good", it's easy to jump to the conclusion that, in general, "natural is good, and unnatural is bad". That's one of the reasons that natural foods, natural remedies, natural childbirth, et cetera, are so popular.
Darwin was one of the first to state, and thousands of other scientists after him have amassed mountains of evidence to support him, that evolution by natural selection is "natural" --- in fact there's no way of avoiding it, and it is one of the most powerful forces of nature.
A common misconception is that it's easy to tell. Many think that the "fittest" people are those who are the smartest, or the fastest, or the strongest. Nonsense. The fittest people are those that have the most babies. It may be that stronger, smarter, or faster people tend to have more babies, but it's not guaranteed. The schizophrenic cult leader who has babies by all his female followers is vastly more fit by Darwin's definition than the handsome, famous, monogamous movie star who has only one child with his wife.
The biological definition of fitness measures the relative fitness of an individual by the number of copies of his/her genes that make it into the next generation. If I have four kids and you have two, and all of our kids make it to adulthood, I am twice as biologically fit as you. In the next generation, there will be twice as many people who are like me than are like you.
At first glance, this definition of fitness seems to say nothing. It seems to say only that the people who have more kids have more kids. This is obvious, but the powerful consequence is this: the kids carry copies of the genes of the parents, so if there is something in the genes that make an individual more likely to have kids, those sorts of genes will be relatively more common in the next generation, so the next generation will tend to have people more disposed to or able to have more kids than the previous.
Most of us think this sort of reasoning is completely immoral, but most of us do not think it's immoral if the species happens not to be human. We breed cows for more meat, better milk production, et cetera. We breed corn for higher yields and disease resistance. We breed weird-looking dogs just because we like the looks of them.
Evolution occurs because of selection acting on differential fitness, and it doesn't matter whether the fitness is "natural" or "unnatural".
But that's just where we're headed, and almost every "natural" drive we have is pushing us toward this end. To avoid catastrophe, we'd had better do something that is unnatural, from the point of evolution and natural selection; we've got to do some combination of lowering our population growth, decreasing our consumption, or somehow figure out how to produce more food/energy/water/et cetera from available resources.
Evolution and natural selection usually works on individuals; it does nothing to preserve a population. We humans, using our abilities of reasoning and communication are probably the only species the earth has ever seen that has the capability of doing something to preserve the species as a whole. But this will require cooperation on a large scale, and we've got four billion years of evolution where non-cooperation (or at most cooperation among a very limited set of humans) was selected for.
Let's hope we can overcome our "natural" tendency to breed and consume until we cause an ecological catastrophe with an "unnatural" large-scale cooperation.
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