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The killer app in the evolution of our hands was our opposable thumbs, which allow humans to precisely hold tiny things between our fingers and the pad of our thumb.
A new take on this question, however, suggests that while the earliest hominids may have been dexterous, they did not have the powerful thumb typical of humans today until later, about 2 million years ago. It was around this time that one of the first species of humans first left Africa, and our dexterity could have been the engine of a more complex human culture that emerged then.
“Increased manual dexterity in the form of effective thumb opposition was one of the first defining characteristics of our lineage, providing a tremendous adaptive advantage to our ancestors,” said paleoanthropologist Katerina Harvati, professor at the University. Eberhard Karls from Tübingen in Germany and responsible author of a new study published in the journal Current Biology.
“It is probably a crucial element underlying the development of a complex culture over the past 2 million years, shaping our biocultural evolution.”
Researchers estimated thumb power in some of our fossil human relatives by virtually modeling a thumb muscle that is important for opposability and movement that brings the thumb into contact with other fingers.
This involved comparing the hold of recent and modern humans, living chimpanzees, and six different hominid species. These six species include one of the oldest – Australopithecus afarensis (Lucy) – and more recent archaic humans such as Neanderthals who existed before and, in some cases, alongside the first Homo sapiens in centuries and millennia before. that we don’t become the only hominin. survivor.
The scientists took into account soft tissue as well as bone anatomy.
“Until now, manual dexterity has primarily been assessed by simply comparing fossils with anatomy present in humans, and assuming that the more anatomically similar a fossil is to the modern human condition, the greater its dexterity and abilities. manual were similar, ”Harvati said by email.
“However, this view is relatively simplistic, because similar efficiency can be achieved by different forms, and also because it does not take into account the effect of muscles. The latter is extremely important, but is of course not preserved in the fossil record. “
Early stone toolmakers in the Australopithecus family who lived around 2 million to 3.8 million years ago did not have the increased manual dexterity that later hominids had, the researchers found. It would have been more difficult to make precise movements like holding a pen to write, but these australopitchecines could have used tools like sticks and unmodified rocks – much like chimpanzees do in the wild.
“The phalanges (bones of the fingers) of Australopithecine hands were generally longer and more curved than those of modern humans (though not as much as living great apes). So they would probably be able to shake your hand, but it would probably do a noticeable difference, ”Harvati said.
Researchers’ The results suggest that the mighty thumb that characterizes the human hand only evolved in some fossil hominid species around 2 million years ago.
Around this time, Homo erectus emerged – the first humans to have body proportions similar to Homo sapiens and the first to disperse from Africa – along with evidence of systematic slaughter of hunted animals and use of aquatic resources. Stone tools also became more sophisticated and were used more widely, expanding early human diets.
“Of course, it is not possible to show a direct association,” said Harvati. “But we are seeing increased cultural complexity over time in the fossil record after around 2 million years, which is the age of the oldest fossil showing increased thumb efficiency in our sample.
“This includes a more systematic use of stone tools, the gradual development of more complex stone tool industries, the progressive increasing dependence on animal resources and, of course, the appearance of Homo erectus, a large hominid. larger brain and body, whose geographic reach has widened. across Africa and Eurasia. “
The study also found that Neanderthals and modern humans had a fairly similar level of dexterity – suggesting it was inherited from a common ancestor.
Tracy Kivell, a professor at the School of Anthropology and Conservation at the University of Kent in the UK, who was not involved in the research, said many hypotheses need to be made in this type of analysis because the muscles are not preserved in the fossil record. It can, however, provide useful information and new ideas to test, she said.
Kivell said the study’s authors did “a great job of managing all of the complexities involved in this type of research to make their results as robust as possible.”
“Many primates are capable of precision and power grips. However, humans are capable of powerful pad-to-pad precision grips, for which a strong thumb is an essential component,” she said by e- mail.
“This ability in humans is often thought to have evolved in response to the use of tools. Being able to efficiently craft and use tools (stone, bones, herbal tools) would allow us to take advantage of new food resources that would otherwise be unavailable or take more time / energy to access. ”
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