The fact that humans have opposable thumbs, and other primates such as chimpanzees do not, suggests that our hands are more evolved to cope with skills such as using tools. Remarkable new research, though, is suggesting just the opposite; our hands are actually fairly primitive, and it is chimps who have experienced changes over time.
The research, published in Nature Communications, was carried out by Sergio Almécija of Stony Brook University in New York and his colleagues. “Human hands have not changed much,” he told IFLScience. “Hands were already like ours today in prehistoric times.”
The team came to their conclusion by studying the hands of modern primates and the remains of early apes and human ancestors. Specifically, they examined the thumb to finger length, which in humans and gorillas is characterized by a relatively long thumb compared to the four fingers, resulting in opposable thumbs. In chimps, their hands are much longer and narrower, and they do not have opposable thumbs.
Human ancestors that were studied included Ardipithecus ramidus and Australopithecus sediba, which lived around 5.6 million and 2 million years ago, respectively. But despite the huge age gap, their hands were not found to be all that different in terms of thumb and finger size. Chimps, conversely, have seen their fingers elongate in that time in order to help them cope with hanging from branches.
“Our hypothesis is that the hand proportions that facilitate a refined human-like ‘pad-to-pad’ precision grasping are one of the earliest adaptations in hominins,” said Almécija.
He added that since hominin hands appear to have changed very little, the hand proportions of A. ramidus were likely similar to the as-yet unidentified last common ancestor of humans and chimpanzees, which possibly existed up to 13 million years ago, suggesting that our hands stretch even further back in time in their primitiveness.
Humans may have had opposable thumbs longer than we thought. Sergio Almécija.
One implication is that the hands of human ancestors were similar to ours today, even when the use of tools began 3.3 million years ago, and did not alter as a result. Instead, changes that encouraged the widespread use of tools among human ancestors were likely neurological and not physical, if the research holds true.
The “bigger implication,” according to Almécija, is that the last common ancestor of humans and chimps was likely more human-like than chimp-like.
He added: “The results of our study show that the hand proportions of living apes are not as similar as previously assumed. In fact, gorillas and chimpanzees are more different from each other than chimpanzees from orangutans, or those from gibbons.”
On whether this could mean that other anatomical parts are also more primitive in humans than thought, Almécija added: “That could be the case.”