Scientists have rubbished a long-held belief that prehistoric humans avoided eating tough plants because they damaged their teeth.
It is now thought hard plant foods may have made up a larger part of early human ancestors’ diet than previously thought.
Scientists in the US discovered even the hardest plant tissues scarcely wear down primate teeth.
‘We found that hard plant tissues such as the shells of nuts and seeds barely influence microwear textures on teeth,’ said Adam van Casteren, lecturer in biological anthropology at Washington University in St Louis.
Scientists studied Bornean orangutan molars to see how hard plants affected enamel.
They found that microscopic pits were not created by hard plant tissue, such as nuts and seeds as was expected.
‘If teeth don’t demonstrate elaborate pits and scars, this doesn’t necessarily rule out the consumption of hard food items,’ Dr van Casteren said.
The study shed light on a little-known group of ancient humans known as austrolopiths which had large, powerful jaws.
It is suspected they had extremely powerful jaw muscles as well, similar to some modern-day primates.
‘All these morphological attributes seem to indicate they had the ability to produce large bite forces, and therefore likely chomped down on a diet of hard or bulky food items such as nuts, seeds or underground resources like tubers,’ Dr van Casteren said.
Researchers attached tiny pieces of seed shells to a probe and repeatedly dragged it across enamel from a Bornean orangutan molar tooth.
A total of 16 different tests were conducted to replicate three sorts of nuts which make up modern primate diets, each with different levels of hardness.
Researchers also dragged the seeds with the same amount of force as a jaw would create.
The seed fragments made no large pits, scratches or fractures in the enamel, the researchers found.
There were a few shallow grooves, but the scientists saw nothing that indicated that hard plant tissues could contribute meaningfully to dental microwear.
The seed fragments themselves, however, showed signs of degradation from being rubbed against the enamel.
Researchers now believe big australopith jaws could have been put to use chewing on large amounts of seeds and it would not scar the teeth.
‘And that makes perfect sense in terms of the shape of their teeth’ said Peter Lucas, a co-author at the Smithsonian Tropical Research Institute, ‘because the blunt low-cusped form of their molars are ideal for that purpose.’
‘When consuming many very small hard seeds, large bite forces are likely to be required to mill all the grains,’ Dr van Casteren said.
‘In the light of our new findings, it is plausible that small, hard objects like grass seeds or sedge nutlets were a dietary resource for early hominins.’