My friend Jen is due to have an impacted wisdom tooth removed. This led to a discussion around the gaming table about each of our experiences with getting our wisdom teeth removed. Some of us were better off than others, needing only upper teeth removed, or suffering lesser degrees of impaction, or growing teeth more exposed to surgery, but we’d all been compelled to surgical removals. Which got me to thinking about evolution.
Homo sapiens sapiens has smaller jaws than our immediate relatives in the evolutionary family tree, which is why we have wisdom tooth trouble: our genes still tell our bodies to produce the same number of teeth in a smaller space. The last teeth to come in get crowed aside, often failing to grow out of the lower jaw at all. Failing to grow out is bad, but growing out part-way is much worse—or would be, in a pre-industrial, pre-surgical environment, where being able to reach the tooth easily for removal doesn’t count for much—because the irregularities and inaccessibility of the partially-grown tooth are magnets for tooth decay. Again, in a pre-industrial, pre-surgical environment, that’s very dangerous, because the blood and lymph vessels serving the jaw are closely tied to those serving the brain; untreated or maltreated tooth decay often leads to death as infections are carried brain-ward. Even today, people who neglect their teeth to an extreme degree occasionally succumb to brain infection.
(Since the change in jaw predates surgery, I’m at a loss to explain how our jaws could have shrunk in the first place. There must be some link to an evolutionary advantage even more important than reducing the chances of death by brain infection. Greater mating potential from the attractiveness of neotenous features?)
The idea that modern medicine renders humans immune to the pressures of evolution and natural selection is plausible only so long as you don’t think very hard about it. Okay, maybe we’re no longer subject to the same evolutionary pressures as animals in the wild, and increasingly rapid changes in society and technology may shorten the timespan over which a given pressure might operate, but that just means we’re subject to different evolutionary pressures. Behaviors are just as subject to natural selection as gross physical features. Perhaps a modern, industrial, urbanized lifestyle selects for greater comfort in enclosed spaces, or the beauty of youth in place of the beauty of health, or a reduced territorial drive. Your guess is as good as mine.
