So about a year & a half ago I was compelled to visit the dentist to get a crown. He informed me at the time that I had a wisdom tooth that would need to come out soon. He expressed surprise that it had not already caused me trouble or pain, and said he would leave it for the time being - the tooth would let me know when it was time to go. This week the tooth started talking to me. It's scheduled to come out on the 8th. Meantime I have to take antibiotics and I have a prescription for pain killers to get me through. I am trying to avoid the pain killers as much as possible - it's just barely tolerable on ibuprofen, we'll see if it gets worse.
Of course this got me thinking about the whole concept of wisdom teeth and why we have them when they cause so much trouble - a rather "unintelligent" design flaw to say the least - and the irony of then calling them "wisdom" teeth is inescapable. Nothing wise about a set of teeth that your mouth doesn't have room for.
The obvious (not necessarily correct, just intuitively obvious) explanation is that in our evolutionary history the modern human mouth (the jaw, really) decreased in size but the number of teeth remained the same as our larger-jowled ancestors. Scientists debate why this event occured: Was it a change in diet and eating habits or the necessary by-product of an increase in brain size? In other words, did the change in diet and subsequent decrease in jaw size allow the development of a larger brain or did the development of the larger brain drive the decrease in size of the jaw? I don't see why these two alternatives are mutually exclusive and I can see how both forces could have been at work simultaneously. Although it's not obvious why a larger jaw for a third set of molars would in itself be disadvantageous for eating softer or cooked foods.
Whatever the ultimate driving force, it seems the wisdom tooth problem is a pretty nice argument for evolution and illustrates the way evolution works- and perhaps more importantly how it DOESN'T work. It produces characteristics that are not perfect, just "good enough" to allow for survival. Who knows, perhaps given more time and a more primitive technological world, the wisdom tooth would not be such a problem - either we would have settled for a larger jaw or the wisdom-toothless trait would have become the norm. As it is, the wisdom tooth is not a fatal (normally) condition and even then it usually causes trouble relatively late in life - thus there's really no evolutionary mechanism for eliminating it.
In cursory research of this topic, I stumbled across this article from the Columbia News Service. Columbia as in Columbia University. It's an article by a journalism student, so I'm more than willing to cut a little slack here, but I still expected to find a pretty accurate and intelligent story. Unfortunately the author completely botched the concept of evolution generally & natural selection in particular. Here's a quote:
Scientists agree the human race is advancing -- if very, very slowly -- along the evolutionary track by shedding unnecessary parts like the wisdom tooth, though there's debate about what is causing it to disappear.
I'll just mention without going into the details that the whole concept of evolution representing some sort of "advance" in any metaphysical or cosmic sense is pretty much a dead topic and a little jarring to see people still discussing it in those terms.
What strikes me more is the Lamarckian explanation for the way in which the wisdom tooth is supposedly disappearing, the idea that we are shedding wisdom teeth simply because we don't need them. I read the whole article looking for a clarification of this simplistic explanation, but there is none. It reminds me of those stories I heard when I was younger about how we are losing our little toes because we don't use them any more. I also looked elsewhere for data that support the idea that we, as a species or even a population in the US, are losing the wisdom teeth at all. I browsed a couple of studies from PubMed that looked at wisdom teeth in a sampling of students. Both put the number at around 10% showing no wisdom teeth (congenitally missing) but neither refer to any change in this percentage over time. So I'm not even sure the general statement is supported by the evidence and I can't think of any plausible explanation for how it would occur. In general, here's what would have to happen.
Assumption: Congenitally missing wisdom teeth is an inherited condition - it is not a result of pre-natal or post-natal nutrition or the texture of the food eaten in early childhood or adolescence. If this trait is becoming more prevalent, then one of the following conditions would have to be met (there may be others, but these are the obvious possibilities.)
1. People who inherit congenitally missing wisdom teeth have an advantage over people who are born with wisdom teeth. By advantage, I mean ONLY that they are able to survive longer and produce more offspring. In the modern world this seems a rather unlikely scenario. I could be wrong, but an article that asserts an increase in the number of people who do not have wisdom teeth (as a result of evolution) needs to address this issue - do a significant number of people die as a result of having wisdom teeth compared with those who do not? Do the wisdom-toothless live longer and thereby produce more offspring? Are they more attractive and therefore find mates more successfully? Again, none of these possible explanations seem plausible.
2. The second possibility is that congenitally missing wisdom teeth is bundled with some other trait that is advantageous - a stronger jaw line, which seems to be a particularly attractive male feature (if less so for females), for example. Again this seems rather implausible, and in fact the opposite would seem more intuitively correct - a stronger jaw line would be more likely to have room for the extra set of molars.
3. Genetic drift - by pure chance a slightly larger number of offspring are produced with the missing wisdom teeth, and over time we have drifted toward a decrease in the incidence of wisdom teeth in our population. Like tossing a coin and getting 7 heads and 3 tails out of ten, this possibility is more likely in small isolated populations (If a subset of a population is getting 7/10 heads, by chance, another subset is just as likely to get 7/10 tails - when they commingle the outcome is back to the expected 5/10 each). I'm not sure this is a plausible answer given the large population size we are dealing with and the constant influx of immigrants from around the world into the gene pool.
I have absolutely no data to support or refute any of these possibilities. I also realize there may be more complicated factors at work. I'm just wondering where the author got her data and arrived at her conclusions. I'm always interested in how people imagine evolution occurs, and Lamarckian "disuse" seems to be a particularly common conception.
PS- Alexbarnett gets the award for most catchy title relating to this topic: An Inconvenient Tooth
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