Even after their first molars emerge, the apes continue to suckle

By Erin Wayman

Web edition: January 28, 2013

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BABY TEETH

This 3.1-year-old female chimpanzee has two lower molars.

Credit: Courtesy of Andrew Bernard

Contrary to scientists’ prior beliefs, the age at which a chimpanzee gets its first permanent molar tooth doesn’t predict when the ape will stop nursing and start eating solid foods. The finding could alter the way anthropologists think about how ancient hominid infants matured.

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OPEN WIDE

Researchers took hundreds of photos of chimp mouths and determined that wild chimpanzees get their first molar by about age 3.

Credit: Courtesy of Andrew Bernard

In many primate species, the appearance of the first molar tooth marks the age of weaning. Researchers have assumed this to be true for chimpanzees, humans’ closest living relatives, and have used the tooth’s emergence in chimps to infer growth and behavioral patterns in extinct hominids. To find out whether this assumption holds, Harvard University’s Tanya Smith and colleagues photographed the gaping mouths of five wild infant chimpanzees in Uganda between August 2011 and December 2012.

Each chimp’s lower first molar emerged by age 3.3, but all of the infants continued to suckle after the tooth erupted — some beyond age 4, the team observed. Therefore, scientists might need to rethink using the presence of the first molar in a hominid fossil as a sign of weaning, the researchers report online January 28 in the Proceedings of the National Academy of Sciences.