Neanderthal thumbs were better adapted to holding tools in the same way that humans hold a hammer, new research suggests.
The findings suggest Neanderthals may have found precision grips more challenging than power squeeze grips.
Precision grips involve holding an object between the tip of the finger and the thumb, and power squeeze grips are where objects are held like a hammer, between the fingers and the palm with the thumb directing force.
Using 3D analysis, Dr Ameline Bardo and colleagues, mapped the joints between the bones responsible for movement of the thumb – referred to collectively as the trapeziometacarpal complex – of five Neanderthal individuals.
They compared the results to measurements taken from the remains of five early modern humans and 50 recent modern adults.
The researchers from the University of Kent found covariation in shape and relative orientation of the joints that suggest different repetitive thumb movements in Neanderthals compared with modern humans.
The joint at the base of the thumb of the Neanderthal remains was flatter with a smaller contact surface and better suited to an extended thumb positioned alongside the side of the hand.
According to the study, published in Scientific Reports, this thumb posture suggests the regular use of power squeeze grips – like the ones humans now use to hold tools with handles.
These joint surfaces are generally larger and more curved in recent modern human thumbs, an advantage when gripping objects between the pads of the finger and thumb, known as a precision grip.
Researchers said that although the morphology of the studied Neanderthals is better suited for power squeeze grips, they would still have been capable of precision hand postures.
However, they would have found this more challenging than modern humans, according to the authors.
Comparison of fossil morphology between the hands of Neanderthals and modern humans may provide further insight into the behaviours of our ancient relatives and early tool use.
The authors wrote: “Results show a distinct pattern of shape covariation in Neanderthals, consistent with more extended and adducted thumb postures that may reflect habitual use of grips commonly used for hafted tools.”
They added: “These results underscore the importance of holistic joint shape analysis for understanding the functional capabilities and evolution of the modern human thumb.”