Systematic stone tool production and use are regarded as one of humanity’s defining characteristics and a pillar of our bio-cultural evolution, closely connected with our increased manual dexterity and ability for precise grasping motions. However, even though heightened manual dexterity is critical for human behavior and subsistence, its role in the development of early human culture remains unclear, as does the timing of its appearance and the hom-inin species with which it was first associated.  

The team addressed this research gap through a new, integrative approach for analyzing fossil thumb bones from different human species - including from early modern humans, Neanderthals, Australopithecus and Homo naledi. The researchers developed an innovative biomechanical model to analyze the forces that the thumb muscles might have exerted in each species and calculated each thumb’s dexterity. For further comparisons, the team also looked at how today’s great apes use their thumbs.

The researchers found that the earliest proposed tool-making hominins of the genus Austra-lopithecus, had consistently low thumb opposition efficiencies, similar to those observed in great apes today. This was also the case for Australopithecus sediba, a species whose human-like thumb proportions had been thought to reflect human-like grasping capacities.

In contrast, more recent hominins, including Neanderthals, the small-brained Homo naledi and early Homo sapiens, all exhibited similarly high levels of thumb-using efficiency. “The fact that thumb opposition efficiency was consistently substantial in the genus Homo highlights the major importance of this evolutionary advantage for human bio-cultural evolution”, Harvati concludes.     

Publication: 

Fotios Alexandros Karakostis, Daniel Haeufle, Ioanna Anastopoulou, Konstantinos Moraitis, Gerhard Hotz, Vangelis Tourloukis, Katerina Harvati: “Biomechanics of the human thumb and the evolution of dexterity”. Current Biology, DOI: 10.1016/j.cub.2020.12.041