Tanya Smith: What we’re doing is finally answering a question that’s been debated for over 80 years, which is whether Neanderthals grew and developed just like modern humans did.
In a study published in November 2010, Harvard anthropologist Tanya Smith provided evidence that humans’ closest prehistoric cousins, the Neanderthals, developed faster and had shorter childhoods, than early humans. She told us that the proof is in their fossilized teeth.
Tanya Smith: There’s this really beautiful record, sort of like rings in tree trunks, that allows us to read the speed and the time of formation, inside teeth.
Smith used powerful X-rays to compare the microscopic growth lines on 3D images of ancient Neanderthal and early human teeth. The counts of these tiny daily growth lines between birth and death revealed that Neanderthal children grew their adult teeth faster than our own species, she said.
Tanya Smith: There’s this correlation, or relationship, between how long you take to grow your teeth, and what your overall growth and development is like. By inference, the fact that Neanderthals are growing their teeth in a relatively rapid way suggests that their overall growth and development was a little different from our own.
Smith said scientists theorize that humans’ long childhood – the longest of any primates – allowed our species more time to develop our brains and social skills, and outlast our Neanderthal cousins.
Tanya Smith: What we did in our study was we looked at a sample of juvenile Neanderthals from across Europe, from different time periods and from different locations, and of different developmental stages. What we found was that those Neanderthals were younger than you would have expected, based on modern developmental standards.
For example, Smith said, her research revealed that a fossil that had been thought to belong to four- to six-year-old Neanderthal child, based on information about its brain size, actually belonged to a three-year-old. That information was hidden inside its teeth.
Tanya Smith: In the work we did in our study, we use this really interesting and new technique called virtual histology. Using powerful synchrotron X-rays, we are able to see inside teeth and actually see these microscopic lines with a very high magnification.
Smith described how in each fossilized set of teeth she studied – and in our own teeth as well – there’s a line she called the “birth certificate,” making a record of birth and allowing age to be recorded through teeth.
Tanya Smith: We used particularly the first molar tooth, because it contains this birth certificate – and we were able to go in, find this line, then reconstruct using this record of development how long each particular tooth took to form.
Smith said this hasn’t been done before, because the X-ray imaging technique is new technology that allows scientists to peer inside fossilized teeth without physically slicing pieces from them.