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.
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.