Credit: iStockPhoto

~ Catherine de Lange

I am in agony. For the last four days I've been struggling to cope with an ever-worsening infection of my wisdom tooth. It's bad enough having a massive new tooth pushing its way through your gums when all the space in your mouth is already taken, but when it also gets hijacked by a bunch of evil bacteria, the pain becomes unbearable.

Which got me thinking: what's all this in aid of anyway? Wisdom teeth are still a bit of a mystery, one of those vestigial body-parts which paradoxically seem to do us more harm than good. In fact, millions of wisdom teeth are extracted each year, and not without risks - it's not unheard of for people to die as a result of wisdom tooth surgery, even with modern medical practices.

There is some comfort in the knowledge that this pain is, indirectly, a trade off for my big brain. Whereas our early ancestors had big jaws and small brains, weaker jaw muscles and therefore smaller jaws helped accommodate a larger skull. So back in the day, our ancestors had plenty of room for this third set of molars, whereas we do not.

The problem is made worse by the fact that with our bigger brains, we figured out how to process our food. Mushier food means less wear and tear on our molars, so there's even less room for the wisdom teeth when they come through. And last year, and international team published findings in the Proceedings of the National Academy of Sciences suggesting that the shift to agriculture and the resulting change to our diets caused our jaws to become shorter, meaning less space for our teeth.

So why hasn't evolution done a better job and got rid of our wisdom teeth? Why is this primitive relic of our ancient ancestors still causing me so much grief? One explanation is that wisdom teeth come through quite late in life, often after people have reached reproductive age, so there are weaker selection forces against them. Or it might be that the genes responsible for molar growth are also important for other things.

As many as 35% of people don't get wisdom teeth at all and in 2000, scientists at the University of Texas-Houston Dental Branch and the Baylor College of Medicine in the U.S. made an unusual discovery which provides important clues about one of the genes responsible for molar growth. They reported a bizarre case in which three generations in one family fail to grow molar teeth at all. One 13-year-old boy in the family was missing 14 of his permanent teeth, and out of 43 family members, 21 grew no molars. Gene sequencing revealed that those family members lacking molars had a mutation in one copy of a gene called PAX 9. But PAX 9 is also known to be involved in body shape and organ development during embryogenesis, and experiments in mice show that when both copies of the gene are faulty, the animals also have more serious problems such as deformed limbs on top of the missing teeth. Maybe the genes involved in molar formation are simply too important to mess with.

On the plus side, wisdom teeth have recently proved they do have some uses. A team of Japanese scientists have managed to extract stem cells from a wisdom tooth which had been frozen for three years, suggesting that tooth pulp could be a good source of stem cells and an alternative to embryonic cells. Maybe wisdom shouldn't be confined to the history books quite yet after all.