The macaques of The Japanese island of Koshima is a smart bunch. Well-known for performing remarkably complex tasks, such as washing sweet potatoes and straining wheat from sand into seawater, they have even been spotted catching live octopuses from the sea.
During continued observations, the macaques’ unique skills quickly spread through the population and provided some of the earliest evidence of local habits among the animals.
I recently visited Kyoto University’s Institute of Primate Research to study the tooth remains of naturally deceased macaques on Koshima Island, one of the world’s oldest primate sites.
This was part of a project to create a database of tooth wear and dental disease in wild primates – but I soon noticed something extremely unexpected. All of the dead macaques had identical – and highly unusual – tooth wear for a primate. And not only that, it looked remarkably similar to the tooth wear commonly found in fossil samples of hominids (humans and our closely related ancestors). I knew I had to investigate further.
Through collaborations with local primatologists and experts in the study of microscopic features on tooth surfaces, we studied the dental remains of 32 individuals in more detail, recording overall tooth wear, fractures and pathologies. . This allowed us to directly compare tooth surface features with published examples in hominid fossils.
Surprising dental similarities
The “toothpick” grooves on the back teeth and the large vertical scratches on the front teeth are thought to be unique to hominids, and most likely caused by the use of distinctive tools. Marks are used as evidence of early forms of cultural habits identified during human evolution.
But since my colleagues and I found these same types of unusual tooth wear in the preserved teeth of deceased wild macaques from Koshima, we attempted to explain the similarities using a combination of extensive literature and ongoing field observations. .
In fossil hominin specimens, large scratches on the front teeth are generally thought to be caused by a type of behavior called “stuffing and cutting” in which an object, such as animal skin, is held between the front teeth and a stone tool used. to cut portions.
Accidental contact of the stone tool with the exterior of the front teeth causes the marks, and it is suggested that by studying the orientation and concentration of the scratches in different areas of these teeth, insight into the straightness or left-handedness can be gleaned.
Also, since “toothpick” grooves usually form between the rear teeth and long, thin, parallel scratches are often found in these grooves, it has long been considered that these grooves must be caused by a tool placed into the space between the teeth and backed up repeatedly. and forward to clear food debris or ease discomfort (hence the name toothpick grooves).
But there is no evidence for these types of tool use in macaques on Koshima Island, or indeed for any behavior that could be considered habitual tool use. Instead, this wear and tear is likely caused by eating shellfish and accidentally chewing and eating sand. Macaques have been seen frequently scavenging for food on sandy beaches – and despite their attempts to wash the sand away, some still get chewed on as there is sand in their droppings.
Crustaceans are also regularly eaten, and macaques use their front teeth to dislodge them from rocks and scoop out the contents. These behaviors probably cause this extreme wear, due to sand, hard shells and rock that regularly come into direct contact with different tooth surfaces.
It’s easy to imagine how wide parallel scratches can form when biting into sand-covered food or trying to dislodge and consume shellfish without tools.
Why root grooves and marks within grooves should form on the back teeth when sand or gravel is chewed requires further investigation, but is likely due to small, hard particles passing over these surfaces during the chewing cycle and during swallowing.
Implications for human evolution
Thus, it appears that normal chewing and food processing can cause these types of wear without the need to infer complex and habitual tool use.
And since there are even more dental similarities between the fossil hominin samples and this group of macaques at the microscopic level – along with high rates of tooth chipping, extreme overall tooth wear, and the beveled appearance of the teeth of front – it must be considered that there is a common cause that has nothing to do with the use of tools.
Of course, it’s true that humans have used tools for a long time, as evidenced by the significant number of stone tools found throughout human evolution. But that doesn’t mean they were responsible for the unusual wear seen on hominid teeth.
In fact, there is growing evidence of sand chewing, and marine molluscs are also thought to have been eaten. If tooth wear in fossil hominins is caused by feeding behavior, further study of their tooth wear can provide vital insight into dietary and behavioral changes during human evolution. And studying primates alive today could continue to offer crucial clues that have been overlooked in the past.
This article was originally published on The conversation by Ian Towle at London South Bank University. Read it original article here.