Neanderthals may have found precision grips (where objects are held between the tip of the finger and thumb) more challenging than power squeeze grips (where objects are held like a hammer, between the fingers and the palm with the thumb directing force), according to new research led by the University of Kent.
Reconstruction of a Neanderthal. Image credit: Neanderthal Museum.
“Much research has debated the technological abilities of Neanderthals (Homo neanderthalensis) relative to those of early modern humans (Homo sapiens), with a particular focus on subtle differences in thumb morphology and how this may reflect differences in manipulative behaviors in these two species,” said lead author Dr. Ameline Bardo from the Skeletal Biology Research Centre at the University of Kent and colleagues.
“We provide a novel perspective on this debate through a 3D geometric morphometric analysis of shape covariation between the trapezial and proximal first metacarpal articular surfaces of Neanderthals in comparison to early and recent humans.”
The researchers used 3D analysis to map the joints between the bones responsible for movement of the thumb (referred to collectively as the trapeziometacarpal complex) of five Neanderthal individuals.
They then compared the results to measurements taken from the remains of five early modern humans and 40 recent modern adults.
They found covariation in shape and relative orientation of the trapeziometacarpal complex 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 is flatter with a smaller contact surface, and better suited to an extended thumb positioned alongside the side of the hand.
This thumb posture suggests the regular use of power ‘squeeze’ grips, like the ones we now use to hold tools with handles.
In comparison, 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.
“Although the morphology of the studied Neanderthals is better suited for power ‘squeeze’ grips, they would still have been capable of precision hand postures — but they would have found this more challenging than modern humans,” Dr. Bardo said.
“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 team’s paper was published online in the journal Scientific Reports.
A. Bardo et al. 2020. The implications of thumb movements for Neanderthal and modern human manipulation. Sci Rep 10, 19323; doi: 10.1038/s41598-020-75694-2