Macaque tooth study casts doubt on view of human evolution

The tooth, the whole tooth and nothing but the tooth has prompted University of Otago dentistry researchers to reassess the way the scientific community looks at human evolution.

Otago’s Sir John Walsh Research Institute dentistry researchers Ian Towle and Carolina Loch collaborated with colleagues in Japan, to study root grooves and large uniform scratches in the teeth of a group of wild Japanese macaques, which had previously only been seen in fossil humans.

"Unusual wear on our fossil ancestors’ teeth is thought to be unique to humans and demonstrates specific types of tool use," Dr Towle said.

"These types of wear have also been considered some of the earliest evidence of cultural habits for our ancestors.

"However, our research suggests this idea may need reconsidering, since we describe identical tooth wear in a group of wild monkeys that do not use tools."

The research raised questions about our understanding of cultural changes during human evolution and suggested the scientific community might need to reassess early evidence of cultural habits, he said.

The study concluded the "toothpick-like" grooves on the back teeth and large uniform scratches on the front teeth of macaques were actually caused by something more mundane — eating shellfish from rocks and accidentally chewing grit and sand with their food.

The skulls of a group of macaques, well-known for remarkable behaviours such as washing foods in water and consuming fish, had been studied for more than 70 years and there was no evidence of them using tools or other items that could cause the unusual tooth wear that had been observed, he said.

Dr Towle has been studying tooth wear and pathologies in a wide variety of primate species and said he was "extremely surprised" to find this type of tooth wear in a group of wild monkeys.

"Up until now, the large scratches in the front teeth of fossil humans have been considered to be caused by a behaviour called ‘stuff and cut’, in which an item such as an animal hide is held between the front teeth and a stone tool is used for slicing.

"Similarly, ‘toothpick’ grooves are thought to be caused by tools being placed between back teeth to remove food debris or relieve pain.

"Although this does not mean hominins were not placing tools in their mouths, our study suggests the accidental ingestion of grit and/or normal food-processing behaviours could also be responsible for these atypical wear patterns."

He believed the findings provided insight into how researchers interpreted cultural changes through the course of human evolution.

"We are so used to trying to prove that humans are unique that similarities with other primates are often neglected.

"Studying living primates today may offer crucial clues that have been overlooked in the past."

john.lewis@odt.co.nz