Handedness in ancient hominins

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Michael Balter writes about the work of Liverpool archaeologist Natalie Uomini, who is studying the evolution of handedness by experiment and attempting to find signs of hand dominance in finished stone tools.

Uomini argues that these findings [in human experiments] are similar to those found in studies of nonhuman primates, in which the degree of handedness varies depending on the complexity of the task they are facing and the level of skill required to perform it. The nut-cracking task required five basic actions, Uomini saysgrasp nut, place nut on anvil, grasp hammer, hit nut, and eat nutwhereas the puzzle required at most three actions (grasp flake, grasp core, fit flake to core.) And along with other researchers who have offered a similar hypothesis, she suggests that the increasing sophistication of hominin toolmaking technologies over time may have selected for a greater degree of handedness. Indeed, Uomini says, the technology-dense lifestyles of early hominins might have required our ancestors to more or less make up their minds about what hands they were going to use to perform complex tasks. Moreover, such hand bias could have aided the learning process as hominins taught each other toolmaking and other skills; a number of studies have shown that people learn manually difficult tasks, such as knot-tying, more easily when they use the same left- and right-hand movements as their teachers.

In other words, once a procedure becomes sufficiently complex, it is likely to require asymmetric spatial operations that will be learned in a biased way from models who have mastered the procedure. But if a model bias is likely to exist, that’s not sufficient to induce selection in favor of added bias. Random changes that reinforced the bias wouldn’t be selected against, but that still leaves us wanting an explanation for the frequency of lefties – as Balter and Uomini both point out.

I’m not sure that this technological explanation actually explains anything. Possibly the causation is in the opposite direction: right versus left handedness tends toward a given frequency for other reasons (maybe pleiotropy, maybe chance) and the use of hands in technology accommodates to the prevailing population mean – to a greater or lesser extent for more or less complex procedural operations.

Still, it’s a very interesting article about some clever ways of applying behavioral science in archaeology.