Thumb dexterity similar to that of people today already existed around 2 million years ago, possibly in some of the earliest members of our own genus Homo, a new study indicates. The finding is the oldest evidence to date of an evolutionary transition to hands with powerful grips comparable to those of human toolmakers, who didn’t appear for roughly another 1.7 million years.
Thumbs that enabled a forceful grip and improved the ability to manipulate objects gave ancient Homo or a closely related hominid line an evolutionary advantage over hominid contemporaries, says a team led by Fotios Alexandros Karakostis and Katerina Harvati. Now-extinct Australopithecus made and used stone tools but lacked humanlike thumb dexterity, thus limiting its toolmaking capacity, the paleoanthropologists, from Eberhard Karls University of Tübingen in Germany, found.
The researchers digitally simulated how a key muscle influenced thumb movement in 12 previously found fossil hominids, five 19th century humans and five chimpanzees. Surprisingly, Harvati says, a pair of roughly 2-million-year-old thumb fossils from South Africa display agility and power on a par with modern human thumbs.