Archaeology news: Evidence our ancestors used stone tools BEFORE opposable thumbs

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The opposable thumb’s evolutionary arrival is commonly associated with the dawn of our ancestors’ first use of stone tools. Most primates – including humans, apes, and some monkeys – boast this incredibly useful trait.

Having opposable thumbs helps grasping things with ease – from picking-up objects to scrolling on smartphones.

However, archaeological evidence now reveals opposable thumbs and tools may not be as intertwined as first thought.

A new study has found opposable thumbs evolved roughly two million years ago and there is evidence indicating human ancestors used stone tools before then.

A genus of early hominins, the australopithecines, are now the most likely early humans with indirect evidence of tool use, between two and three million years ago.

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This latest archaeology suggests their thumbs were more similar to those of chimps than to yours our mine.

Although australopithecines had improved manual dexterity, their thumbs remained unable to achieve the same extent of efficient opposition as ours.

Professor Eberhard Karls, a University of Tübingen paleoanthropologist, said: “Increased manual dexterity in the form of efficient thumb opposition was among the early defining characteristics of our lineage, providing a formidable adaptive advantage to our ancestors.

“These consistently high dexterity levels in species of Homo are indicative of the great adaptive value of thumb opposition for human biocultural evolution.”

This study is all the more remarkable as it is the first successful attempt to pinpoint when efficient thumb use arose in human history while correlating it with tool development.

In 2011, an Australopithecus, dubbed A. sediba, alive approximately two million years ago, was believed to boast human-like precision grasping.

And researchers in 2015 discovered another species Australopithecus africanus had a bone pattern in its thumb and palms they suspected could have allowed for forceful opposition of the thumb more than two million years ago.

However, this new research reportedly refutes both studies, by relying on the thumb’s biomechanics instead of thumbs’ comparative anatomy.

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In order to do so, the team focused on a single muscle and joint in the hominin hand, called the opponens pollicis.

This is considered to be crucial for thumb opposition, allowing flexion at the trapeziometacarpal joint (TMC).

The location of this muscle, its pathway and its general areas of attachment were compared among a variety of fossils of human species.

Dr Alexandros Karakostis, a University of Tübingen biomechanics expert, said: “Our methodology integrates cutting-edge virtual muscle modelling with three-dimensional analysis of bone shape and size.

“Importantly, we were able to validate the predictions of our models by confirming that the differences observed between living taxa – chimpanzees and modern humans – reflect those reported from past experimental studies.”

While Neanderthals (Homo neanderthalensis) exhibit similarly high degrees of manual dexterity, other hominins did not, with both thumb efficiency and dexterity in all Australopithecines consistently lower.

Even the latest species of Australopithecus, A. sediba, showed lower flexion at the TMC joint.

And early hominins from this time period, found at the Swartkrans site in South Africa, had hands much more similar to our own.

And Dr Karakostis goes so far to claim the Swartkrans’ thumb mechanics are halfway between chimpanzees and modern humans.

He said: ”One of the greatest surprises was to find that hominin hand fossils from the Swartkrans site in South Africa, which date to ca. 2 million years ago and are attributed to either early Homo or to the extinct hominin side branch Paranthropus robustus, could achieve a thumb-using dexterity similar to that of modern humans.”

This dexterity may explain why the Swartkans site hominins are considered the earliest users of fire and the first to begin butchering large animals in South Africa.

The researchers added how this shift may well explain how this created to “a significant evolutionary advantage, which might have been part of the crucial bio-cultural developments taking place after two million years.”

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