Modern humans are mostly right-handed, which is weird. After all, other apes hand preference is more evenly split 1. So what changed? Well, a group of researchers are studying fossils to try and find out. In the process, they've stumbled upon the first ambidextrous person in our family 2.
Additionally, they're making progress towards their actual goal. Their discoveries are also pushing back the rise of the right-hand a few hundred thousand years 2.
Hands behind the brain
The ambidextrous fossil in question is one of 9 individuals Poza-Rey and colleagues were studying. All of them belong to an ancient human species hailing from the mysterious pit of bones, chosen because that enigmatic cave preserves fossils extremely well 2.
As a result of this, Poza-Rey et al. were able to study the brains of these fossils. Or at least, the brain imprints left behind on the inside of the skull. Since the brain develops an asymmetry depending on what hand you use, they were hoping to find similar evidence in the fossil skulls 2.
These fossils also contain well-preserved teeth. Like Neanderthals, this ancient species would often use their teeth as tools; holding material taut as they worked it. The resulting damage would vary, depending on which hand they were using 2.
Thus, these fossils gave Poza-Rey et al. a unique opportunity. They could carry out two tests of their handedness; providing a chance to cross reference the reliability of either method 2.
Sure enough, the majority of fossils appeared to be right-handed, as you might expect for a human species. And in most, this conclusion was supported by both the teeth and the brain. However, one individual was different. Their brain seemed left-handed, whilst their teeth showed they used their right hand more often 2.
It seems Poza-Rey had found an ancient, ambidextrous individual 2.
Ambidextrous history
This mysterious individual was known as endocranium 6, being the 6th endocranium investigated by Poza-Rey and colleagues. It seems that their methods may be inventive, not their naming conventions.
Boring names aside, it was clear they'd found someone who naturally favoured the left hand, yet was using the right hand a lot. This tells us more than just "Endo 6 was ambidextrous". It tells us that, despite this skill, they still found themselves mostly using their right hand.
There are many stone age scenarios that could lead to this. Maybe Endo 6 got into a tussle with a wild beast, injuring their left hand early in life and forcing them to adapt. Or perhaps their teacher was right-handed, and Endo 6 was lacking the ability to transfer the techniques he was learning to his left hand.
With only small fragments of their life left, Poza-Rey et al. were unable to tell what was driving Endo 6's behaviour. But one thing is clear: their mates were all right-handed.
This shows our lineage was right-hand dominant since at least 430,000 years ago; nearly doubling previously known estimates. What's more, we didn't inherit this dominance from Endo 6's group; as they don't seem to be our direct ancestors.
As such, we both probably got this trait from our last common ancestor, even further back in time. The human family, it seems, has favoured the right hand for hundreds of thousands of years.
But for just as long, there have been people - like Endo 6 - bucking the trend.
References
- Hopkins, W. (1996). Chimpanzee handedness revisited: 55 years since Finch (1941) Psychonomic Bulletin & Review, 3 (4), 449-457 DOI: 10.3758/BF03214548
- Poza-Rey, E.M., Lozano, M. and Arsuaga, J.L., 2017. Brain asymmetries and handedness in the specimens from the Sima de los Huesos site (Atapuerca, Spain). Quaternary International, 433, pp.32-44.