Caroline Spry


Ancient Teeth Reveal Clues to Why More People Are Right-Handed

Where are all the lefties?


Roughly 90 percent of humans are right-handed, and this is one of the traits that separates us from most other primates who don’t really show any overall preference for left or right handedness.



It is less well-known that brain lateralization, or the dominance of some cognitive processes in one side of the brain, is a distinctive feature of humans, and one associated with improved cognitive ability.

Could handedness have played a role in brain lateralization? Ancient stone tools made and used by our earliest ancestors reveal some clues.

Use of Tools


See also: Neanderthal Bone Scars Reshape What We Assume About Their Behavior


While this relationship is not straightforward, it would appear that, in most cases, handedness and brain lateralization go hand in hand (pun intended).


Without matching left and right sets, it is impossible to examine differences in size and shape to determine which hand an individual favored when completing manual tasks.

Teeth, on the other hand, tend to survive relatively well in the fossil record and can preserve scratches, or “striations,” that establish handedness.

In an earlier study, researchers noted striations on the front side of teeth belonging to European Neanderthals. They hypothesized that these marks were made when material was held in one hand and gripped between the front teeth and worked by the other hand with a stone tool, with the stone tool occasionally striking these teeth.



The subject of the new study — an ancient upper jawbone — provides the oldest evidence for right-handedness known in our genus Homo.


Marks on Teeth


Interestingly, nearly half of all striations were right-slanting. Right-slanting striations were particularly dominant on four of the front teeth (left and right central incisors, right second incisor, and right canine).


The Homo habilis jaw is important as it provides the oldest evidence for right-handedness in the fossil record. But it is also significant as it suggests that a major level of brain organization had occurred in humans by at least 1.8 million years ago.

See also: The Evolution of Round Brains Ushered in the “Human Revolution”

This brain development enabled us to master crucial early skills such as stone tool making and potentially also paved the way for language development. Right-handedness, therefore, means a lot more to us than simply a preference for using the right hand.

Just some food for thought next time you are brushing your teeth, sending a text message, or high-fiving someone.

This article was originally published on The Conversation by Caroline Spry. Read the original article here.