By Erika Owen
October 26, 2016
Three perspectives of the OH-65 maxilla. a. Palatal view; b. labial view; c. close-up of the two central incisors showing concentration of labial striations.
Courtesy of David Frayer

A new fossil discovery has researchers scratching their heads about how old hand dominance is in humans.

The fossil, which is a 1.8-million-year-old jaw bone, has a number of scratches that indicate a right-hand dominance. This is currently the oldest fossil that shows a tendency for dominant hands. A study in the Journal of Human Evolution found that the fossil is four times older than the previous record holder.

So, how exactly can they take a few scratches and tell that the person was right-handed? A series of small cuts are visible on the lip side of the incisor and canine teeth is the answer. These cuts ran from left to right, and analysis of the cuts showed that they were most likely caused by a tool held in the right hand and used to break food into pieces while being held in the specimen's mouth.

“We already know that Homo habilis had brain lateralization and was more like us than like apes,” David Frayer, the lead author of the study and a University of Kansas emeritus of anthropology, said in a statement. “This extends it to handedness, which is key.”