A
study of juvenile hominin jaws dating from 1 to 4 million years ago
suggests early human species grew at widely different rates.
Tanya Smith of Harvard University
says that the teeth of juvenile hominins grew in a way that was unlike
those of either modern humans or apes. “We calculated the age of death
of 16 fossil individuals that lived between about one and four million
years ago, and were able to look at how their teeth formed relative to
living humans and chimpanzees of the same chronological age,” she
explained. Rather than slicing into the teeth and examining their
structures with microscopes, Smith and her colleagues used high-powered
x-rays generated by a synchrotron to produce super-high-resolution
images of the internal structures of the teeth. Then by counting the
daily growth lines, they were able to determine an exact age for each
individual. The team discovered a wide variation in the speed of
development across the fossil species. “These fossil species have to be
seen independently, as having their own evolutionary trajectory that is
not identical to any living animal,” she concluded. To read about the
evolution of the ability to throw, see "No Changeups on the Savannah."
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