Oldest Modern-Looking Human Hand Bone Could Shed Light On Our Evolution

The bone is thought to have come from a little finger. Jason Heaton.

At what point in human history did we switch from tree-swingers to ground-dwellers? A new discovery published in Nature Communications could help to answer this question, and also provide further information on how we began to use stone tools.

Humans and chimpanzees are believed to have shared a common ancestor up to 13 million years ago, but the specifics regarding our separate evolution remain a bit of a mystery. One key tool in working this out has been studying the hands of humans and chimps, to see how they have differed over time.

This latest discovery by a team from the Institute of Evolution in Africa (IDEA), based in Madrid, reveals the earliest modern-human-like hand bone known of so far, dating back 1.84 million years. It was found at Olduvai Gorge in Tanzania. The bone is thought to be from an unidentified modern-looking hominin (human ancestor) lineage, similar to Homo erectus, that originated in East Africa and lived alongside other ancient hominins called Paranthropus boisei and Homo habilis. But this hand is more similar to modern humans than any other.

Called Olduvai Hominin (OH) 86, the finger bone (phalanx) suggests that human hands took their present form early in our evolution – but have barely changed since. It is thought to be from the little finger of a hand, and its importance is due to the bone being straight. Older hand bones have been discovered, but they are curved – and thus more suited for living in trees. “The discovery shows the species was 100% committed to living on the ground,” lead researcher Manuel Domínguez-Rodrigo from IDEA told IFLScience.

It is thought that human ancestors started to use tools around 2.6 million years ago (although some research pushes that back to 3.3 million years), so one would expect hands to have adapted by then. Finding evidence for this, though, has been difficult, making this discovery of great significance.

Its similarity to modern human hands also supports previous research that our hands are relatively primitive. “If we judge from this fossil, we can basically say in almost two million years at least, the human finger has not evolved at all,” said Domínguez-Rodrigo.

Evolving straight hand bones likely allowed our ancestors to use their fingers to more easily grip objects, alongside the evolution of opposable and elongated thumbs.

To further solve the mystery of how human hands evolved, Domínguez-Rodrigo said the team needed to find more bones from the same hand, or another older than two million years, to understand when the bones began to lose their curvature.

Image in text: Researchers at the excavation site. M. Domínguez-Rodrigo.

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