Rather, this is a post intended to clear up some popular misconceptions about how evolution works. I've been meaning to write it for a long time, and some comments made at a Dragon*Con panel reminded me that I still haven't ranted about this in my journal. So, it's high time to get my rant on!
There are two popular notions about evolutionary processes that I hear all the time, often from folks who ought to know better, and they tend to get under my skin. The first is that evolution is no longer operating on human beings; the second is that evolution is goal-directed, that it makes a species "better." Ready? Here we go!
Evolution still operates on people, just as it always has
"Evolution is about survival of the fittest," people say. "Today, thanks to the miracles of modern technology, people who would have died a hundred or a thousand or ten thousand years ago can be kept alive. They don't die off, so their genes still spread. So that means we've stopped evolving."
Fine, except that it's wrong. Evolution isn't about survival of the fittest. That wasn't Charles Darwin's phrase; it was coined by Herbert Spencer, and was included in On the Origin of Species only at the fifth reprint, as it had become popular by that time.
But evolution is not, and never has been, abut "survival of the fittest." That's an overly simplistic and inaccurate view of how evolutionary processes work. Evolution is about the propagation of those genes which most enable an organism to...propagate its genes. What's good for the gene is often, but not necessarily, what's good for the organism; a gene that shortened its host's life by fifteen years but increased the probability that its host would reproduce by .01% would do quite well in the evolutionary game.
(As a segue, I've frequently heard an argument against transhumanism in general and life extension in particular that says "Mortality and a finite life expectancy must be good for us. If they were not good for us, then we would not have evolved to have a finite life span. So the fact that we have evolved in such a way means that there is some benefit to being mortal." This argument does not hold water, because the bulk of our evolutionary heritage comes from a time when most members of the species would die through accident, disease, or predation far, far before they would die of old age. A gene that conferred immortality offers no reproductive benefit to a species whose members are killed by leopards, diseases, tumbles off a cliff, or each other before they're thirty. Ergo, such a gene would not be selected in favor of. We have genes that confer mortality because there's no advantage to genetic immortality.)
Evolution is not about survival of the fittest. It's about the genes that spread. Evolution needs only three things to operate, namely:
1. A population whose individuals are different from one another;
2. A system whereby those differences are heritable; and
3. A system whereby those differences make a difference in how likely an individual is to reproduce.
That's it. That' all it needs. And yes, you have those things in humanity. We are not all the same; the differences between us can be transmitted to our children, and sometimes, those differences make a difference in how likely we are to have children, or how many children we have.
Contrary to the crude understanding of evolutionary processes so common in pop culture, it is not necessary for individuals who have a particular trait to die for that trait to be selected against. If a particular gene--a gene making its bearer more likely to have asthma, say--decreases the odds that a person will reproduce by 0.01%, that's enough. If even one person out of ten thousand has one fewer child because of a particular gene, then evolution is still working.
Modern medicine keeps many people alive today who would die in a pre-industrial society. That does not mean that people with detrimental genes have exactly the same number of children at exactly the same rate as people without that gene. As long as a particular gene has any impact on the number of children its hosts have, however slight, evolution still works.
Evolution is not goal-directed
Evolution does not make a species "better" for any value of "better" that people often use. Evolution favors genes that make its hosts more likely to reproduce. That's it. A gene that causes you to die of a horrifying, debilitating cancer after you hit menopause isn't going to be selected against.
Furthermore, evolution is completely blind with regards to "better" and "worse" as human values. At the panel, one person used Down's syndrome as an example of how evolution no longer applies to human beings. If people with Down's, he reasoned, have children, then how can evolution make the human species better?
This question falls down on a number of levels, and shows a lack of understanding of what evolution is. Down's syndrome is not generally heritable; it's caused by a particular genetic malfunction that does not, usually, affect the gametes.
But leaving that aside for the moment, let's assume that it is heritable. What does that mean? If people with Down's syndrome had more children than people without it, then from an evolutionary perspective, Down's syndrome would be "better." From an evolutionary standpoint, there is one and only one definition of the word "better," and that is "more likely to reproduce."
I mean, if you think about it, I am a worst-case scenario. I have not had children at all, and I have even opted for voluntary sterilization, so I never will have any children. My particular collection of genes is a dead end. I am, evolutionarily speaking, the poorest possible outcome. From the perspective of the processes we're talking about, a person who has Down's syndrome and has children is better than I am.
It frustrates me that American culture is so divided and American politics is so wrapped up in the idea of evolution, yet very few people even understand what "evolution" is. They feel passionately about it, but they're incapable of articulating the most basic principles of evolutionary biology.