New study on teething in chimpanzees

The Kanyawara chimpanzees are the focus of a recently published study in the Proceedings of the National Academy of Sciences examining patterns of tooth development. Researchers from the Kibale Chimpanzee Project partnered with Harvard Professor Tanya Smith to determine the age at which infant chimpanzees in our community erupt their first molar teeth. Our two wildlife photographers, Ronan Donovan and Andrew Bernard, spent two years in the field photographing infant chimpanzees in situations when their mouths would be open enough to see if their back teeth had come in. I’m not sure about Ronan and Andrew, but I can certainly think of worse ways to spend time than photographing baby chimpanzees playing with each other!

Ronan Donavan photographing the Kanyawara chimpanzees. Photo by Alex Georgiev.

We obtained thousands of photographs and were able to determine that our infants erupted their first molar teeth before the age of 3.3. years. Interestingly, when we compared this pattern to our long-term behavioral data we found that infants continued to nurse long after these teeth came in. This was surprising since primate-wide patterns indicate that molar tooth emergence is related to the period of weaning. Instead, we found that molars come in around the time that infants begin showing adult-like patterns in solid food consumption. This is the first study of a wild population of primates that has both the dental and corresponding long-term behavioral data which means we can really test the relationship between tooth emergence and feeding/nursing behavior for each individual.

Azania, one of our female infants, showing that both of her lower first molars (M1s) have erupted before this photo was taken at age 3.1 years. Photo by Andrew Bernard.

Understanding the timing of these developmental milestones in wild chimpanzees is particularly important because evolutionary anthropologists have been debating for years whether early humans followed ape-like or human-like patterns of growth. Since chimpanzees are our closest living relative, it is important to make sure that we document their development before we can fully interpret the fossil evidence. Prior to this study, almost all the research on dental development in chimpanzees came from captive individuals or from a small sample of skeletons collected in the wild and it is unclear how representative these data are of living wild animals. By using this novel photographic approach, our study shows that molar eruption in our chimpanzees is not delayed relative to captive animals and both are very similar to data gathered from fossils of early human ancestors.

For more information about this study and to see more photos and videos of our infants showing off their teeth, please check out our detailed press release here: http://www.heb.fas.harvard.edu/Press3/

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