pz

It's interesting that you'd bring that up, since it is not, strictly speaking, genetic -- it can't be.

Biff the unclean

It can't be? Why wouldn't the size shape of you bones be genetic?

pz

There's more to it than genes. There is, however, a more intuitive way to see why: how many people do you know of who have died or failed to reproduce because their jaws are large enough to accommodate their wisdom teeth? How would the frequency of putative alleles that specify the size of the jaw have changed so rapidly (in the last century) with so little apparent affect on the reproduction of their bearers?

Doubting Didymus

That, pz, is an excellent point. However, doesn't the argument then reject any kind of natural selection at all in this case? What, then, is driving the change?

Biff the unclean

An impactful thought

Celsus

Did it have anything to do with molarcular analysis?

pz

Yes -- isn't that an interesting phenomenon? It's kind of like the Flynn effect.

(Although evolution is not just natural selection, so it isn't necessary to restrict it to just that mechanism. I don't think drift could be responsible, either.)
What a good question. I presume you agree that it can't be driven by differential reproduction?

I'd have to answer with environment. Diet and cultural factors.

Doubting Didymus

Of course, but I admit that it is usually the first place I usually look for an evolutionary explanation, especially when the phenomena looks like an adaptation (which this doesn't).

What about 'use it or lose it'? Can the wisdom tooth problem be veiwed in the light of historical statistics? The first question I would ask is; has the phenomena increased in frequency since people have been removing problem teeth? This may not be accessible information, however.

It has no benefit I can see, so it is my guess that it isn't an adaptation. In veiw of this, I will agree that natural selection is not a player.

Sounds good, but the question is resolvable if we could test the trait for heredity. Do certain groups of people not develop the problem wisdom teeth? If so, do any people born to problem-prone parents still develop their problematic jaws if they grow up in a different environment?

Unless, of course, you are suggesting that there are maternal effects, with the diet of the mother affecting these traits in utero.

pz

That's interesting. Adaptation is usually my last assumption.
It has, but I definitely would not be looking for a Lamarckian explanation.
No, this doesn't address the issue. There is a heritable component, I'm sure. The problem is that we cannot explain the phenomenon as seen in modern populations with changes in the frequency of alleles. It's too fast, and these populations have not experienced anywhere near the kind of mortality or differential reproduction to fit the observation. The kind of selective pressure that would cause a 10% increase (to pick a conservative arbitrary number) in the frequency of such an allele over 3-5 generations is tremendous and would be noticeable.

Some other explanation is necessary -- that's what's interesting about the problem.

Doubting Didymus

I know, it's kind of a bad habit.

Do you really think that is what I was implying, or are you making a joke? What I was implying is 'use it or lose it'. Like our broken vitamin C synthesis, I imagined that the removal of the selection pressure to keep the jaw long may have resulted in atrophy, which I now realise on second thoughts is silly. As you say, there IS no selection pressure, as no-one is severely encumbered in the reproductive stakes by having this problem.

I don't see that problem at all. In this case, any problems with genetic explanations are just as problematic for any other heritable explanations. Unless you are suggesting that there is some heritable factor that can evolve much faster then genes, I think we must be looking at non-heritable explanations.