Without natural selection

I've blogged about this before, but I think I have a new way of explaining this, so at the risk of repeating myself, here goes:

I remember hearing this example from a Genetics class in college. In every generation of wild rabbits, different rabbits have different lengths of hair, some long, some short, and some medium. The rabbits with shorter length hair get too cold at night, leaving them susceptible to disease, so they tend to be selected against. The rabbits with longer length hair tend to overheat and can't run as fast when being chased by predators, so they tend to be selected against. By the time of the next breeding season, you tend to have a predominence of medium haired rabbits. However, the genes for hair length in rabbits are particularly susceptible to mutation, so that by the next generation, you still have roughly the same proportions of long/medium/short haired rabbits.

Evolution has selected for rabbits with a high mutation rate in the hair length gene because the weather often changes from year to year, and can go in cycles such as the ice ages. This high mutation rate results in a loss of reproductive efficiency each year, but it helps them adapt to changing conditions from year to year. Say, for example, that the weather begins to get colder from year to year. Each year, instead of the medium haired rabbits being selected for, it's the longer haired rabbits that get that survive best. Their offspring will again show a variability in hair length, but now median hair length will center around the hair length of the longer haired rabbits.

Now, what would happen if the rabbits suddenly developed high technology? They would have central heating, so the shorter haired rabbits wouldn't get too cold at night, and they'd have guns to protect them against predators, so the longer haired rabbits wouldn't get eaten. By the next breeding season, all of the rabbits would be able to reproduce. They'd probably have birth control, so we wouldn't have to worry about over population, but the shorter haired rabbits would produce who's hair length varied around the hair length of the shorter haired rabbits, and the same with the longer haired rabbits. With each subsequent generation, the extremes in hair length would get shorter and shorter, and longer and longer, on each end of the scale. As their technology got better, they would be able to support even greater extremes of hair length. After several generations, you'd have nearly naked rabbits running around with big old shaggy rabbits.

Now, let's apply the same principle to humans, who really do have technology. The concept of highly mutable regions of DNA is a common strategy, so we surely have some as well. In a primitive culture, where natural selection is still at play, the extremes of any particular feature are selected against, so, although they appear in each generation, the majority of each generation is centers closely around the median. But in a highly technological society, the extremes survive to produce offspring, so each generation becomes more and more extreme, and the extremes make up a larger proportion of society.

One obvious charactertic that we have a large variety of in our current society is weight. We see a lot of variation in individual weight in our society, and I think we see more variation in more modern societies than in primitive societies, but it's hard to say if this is because of the principle I'm describing, or if it's because of other factors, e.g. more availability of food on the one hand, and a culture that prefers skinny people on the other.

Another candidate for this principle is mental stability, and intelligence. I don't really know if there is an increase in variability in these traits in our society, but because our species has see a lot of change in this area fairly recently in our evolution, it wouldn't surprise me if genes affecting the brain are highly mutable. After all, we're obviously descended from individuals who had mutations that affected the brain.