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Neanderthal thumbs were better suited to holding tools in the same way humans hold a hammer, new research suggests.
The results suggest that Neanderthals may have found precision grips more challenging than power take-offs.
Precision grips involve holding an object between the fingertip and thumb, and power compression grips are where objects are held like a hammer, between the fingers and palm with direct thumb force.
Using 3D analysis, Dr. Ameline Bardo and colleagues mapped the joints between the bones responsible for motion of the thumb, collectively referred to as the trapeziometacarpal complex, of five Neanderthals.
They compared the results with measurements taken from the remains of five early modern humans and 50 recent modern adults.
Researchers at the University of Kent have found covariations in the shape and relative orientation of the joints that suggest different repetitive thumb movements in Neanderthals than in modern humans.
The joint at the base of the thumb of the Neanderthal remains was flatter with a smaller contact surface more suited to an extended thumb positioned along the side of the hand.
According to the study, published in Scientific Reports, this thumb posture suggests the regular use of power compression grips, such as those 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 grasping objects between the finger and thumb pads, known as precision grip.
The researchers said that although the morphology of the Neanderthals studied was more suitable for PTOs, they would still be capable of precision hand postures.
However, according to the authors, they would have found it more challenging than modern humans.
Comparing the fossil morphology between Neanderthal hands and modern humans can provide further insight into the behaviors of our ancient relatives and early use of tools.
The authors wrote: “The results show a distinct pattern of shape covariation in Neanderthals, consistent with more extended and adducted thumb postures that may reflect the habitual use of grips commonly used for handled instruments.”
They added: “These findings underscore the importance of holistic joint shape analysis for understanding the functional capabilities and evolution of the modern human thumb.”
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