Research press release


Scientific Reports

Archaeology: Neanderthal thumbs better adapted to holding tools with handles

ネアンデルタール人の親指は、現生人類がハンマーを握るのと同じように、石器を握ることによく適応していたことを報告する論文が、Scientific Reports に掲載される。この知見は、ネアンデルタール人にとっては、「精密グリップ」(親指とその他の指の指先に挟むように物体をつかむ方法)が、「パワーグリップ」(ハンマーのような物体を親指以外の4本の指と手の平で包み込み、親指が力を制御して物体をつかむ方法)よりも難しかった可能性を示唆している。

今回、Ameline Bardoたちの研究チームは、3次元解析を用いて、5人のネアンデルタール人個体の親指の動きをつかさどる複数の骨(「大菱形中手骨複合体」と総称される)の間の関節をマッピングし、その結果を5人の初期現生人類の遺体と50人の現代の現生人類の成人から得られた測定結果と比較した。




Neanderthal thumbs were better adapted to holding tools in the same way that we hold a hammer, according to a paper published in Scientific Reports. The findings suggest that 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.

Using 3D analysis, 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, and compared the results to measurements taken from the remains of five early modern humans and 50 recent modern adults.

The authors 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 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.

doi: 10.1038/s41598-020-75694-2


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