Fangs for the memories

Compared with other species, humans have childhoods that are unusually long and demanding - especially for parents. And they are getting even longer.

- PAUL LITTLE

You can find Brenna Hassett described variously online as a bio-archaeologist, biological anthropologist, or an osteo-archaeologist.

"I study the human remains part of the human past," explains Hassett, a researcher at University College London. "The skeletons and particularly the teeth. That falls under something called biological anthropology, but I also do the digging, which is the archaeology." So, a sort of dental amalgam.

Her book Growing Up Human is a millennium-spanning, multifaceted account of how and why we have evolved to have a childhood that is unique among species. And it all comes from looking at old teeth.

"Teeth are essentially a fossil in your mouth," explains Hassett. "A tooth forms once, so it has a series of incredible regular structures, which means we can tell daily episodes of growth while your teeth are forming, which is, of course, childhood."

Fortunately for her research, which clearly runs on molar power, teeth tend to stay around even after other human remains have disappeared. "They capture the chemistry of the growing environment; they capture the stresses and the diseases that kids pick up. They are a brilliant record."

Over the course of human evolution, teeth have changed as what we eat has changed.

"When your teeth come into your mouth is linked to different life history goalposts. When most primates stop breastfeeding, they get that first molar, because they're going to chew food now and they need that to happen. Your second molar comes when you're able to eat all the foods all by yourself. And then you get that third molar[wisdom teeth], the one that gives us humans so much trouble, at sexual maturity."

Drilling down, as it were, Hassett can work out the daily schedule of how animals were growing. It is possible, for instance, to deduce that a two-and-a-half-million-year-old fossil that looks like a 6-year-old's teeth is actually from a 3-year-old.