"Teeth are like the safe-box of the genetic code," Martinón-Torres said.
That's because—compared to bones—teeth change shape very little once they are formed, and their shape is strongly influenced by genetics.
The researchers classified each of the teeth using more than 50 indicators, such as fissure patterns, overall size, and length-to-width ratio.
"We looked at the entire landscape of the teeth—the mountains, valleys, ridges—everything," Martinón-Torres said.
What they found is that European teeth were more similar to Asian teeth than they were to African teeth.
However, the results don't rule out African influence on European genes.
"This finding does not necessarily imply that there was not genetic flow between continents," Martinón-Torres and colleagues write in their paper, "but emphasizes that this interchange could have been both ways."
The work will be published in tomorrow's issue of the Proceedings of the National Academy of Sciences.
Rather than a one-way stream of people coming from Africa, Martinón-Torres and colleagues think there must have been a more fluid pattern of migrations.
"Just because people had come out of Africa didn't mean that they couldn't turn around and go back again," she said.
The researcher also believes that climate, food, and geography were major influences on hominid migration patterns.
The Sahara, for example, presented a big barrier for movement out of Africa and directly into Europe (see photos and read a related feature about athletes who ran across the Sahara earlier this year).
Rather than struggling across the Sahara, it appears that human ancestors spread in many directions before arriving in Europe.
Erika Hagelberg, a geneticist from the University of Oslo in Norway, is impressed with the study, but cautious about how it should be interpreted.
"The study shows that the genetic impact of Asia on Europe is stronger than that of Africa. But the teeth can't tell us the direction or the time when people migrated," she said.
Nonetheless, the new study does complement direct gene studies and supports the idea that hominids evolved independently in many different parts of the world.
"The fossil teeth are a way to study the traits of past peoples," Hagelberg said, "and help balance the work being done on the genes of people alive today."
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