Whether it’s calluses, osteoarthritis, or the “phone pinky,” our hands tell a story and can reveal a lot about the lives we live and the daily items we use. But what about the hands of our ancient human relatives?

According to a new study, published in Science Advances, two hominin fossil hands showed surprising bone structure and added complexity to the story of human evolution.

“This work offers yet more evidence that human evolution is not a single, linear transition from upright walking to increasingly better tool use, but rather characterized by different ‘experiments’ that balanced the need to both manipulate and to move within these past environments,” said senior author Tracy Kivell in a press release.

Ancient Hands From Ancient Human Relatives

This new research focuses on two fossil hand skeletons found in South Africa belonging to two different ancient human relatives: Australopithecus sediba and Homo naledi.

The two ancient groups appear to have significantly different bone morphology, especially in their fingers. But both fossils suggest that A. sediba and H. naledi were likely using stone tools. The structure of their hands and wrists is more common with modern human dexterity than that of chimpanzees and gorillas. 

“Since stone tools are found in South Africa by at least 2.2 million years ago, and many primates are all excellent stone tool users, it is not surprising that A. sediba and H. naledi would be dexterous tool users as well,” said Kivell in the press release. “However, how exactly they used tools and if they manipulated their tools in similar ways is unclear.”

Although they share a skilled use of tools, A. sediba and H. naledi showed significant and surprising differences in their hand and finger bone structure. 

To identify these differences, scientists looked at variations in the internal structure of the fingers, specifically investigating the cortical bone. Bone, like our skin and other living tissue, can adapt its structure based on things like repetitive use and load bearing. The higher the load, the thicker the bone.

By analyzing the internal cortical thickness of the two fossils, the team was able to uncover how each of these ancient humans likely used their hands. 

Read More: Was Australopithecus sediba Our Ancestor?

Ancient Human Tool Use and Climbing

The A. sediba fossil was discovered in 2010 and dated to about two million years ago. The cortical bones in the middle of its fingers were similar to those of apes. The thumb and pinky finger were closer to those of humans. What this suggests is that A. sediba used their hands for multiple daily activities that involved dexterity, including tool use and climbing.

The results for H. naledi are more unique and unusual. This hand fossil, found deep in the Rising Star Cave system in 2015 and dated to around 250,000 years ago, also showed human- and ape-like bone structures but in unexpected places. Different parts of each finger showed distinct cortical bones, with the middle of the finger being ape-like and the bottoms of the fingers, specifically where the fingers meet the palm, as more human-like.

“This distinct pattern was unexpected and indicates that H. naledi likely used and loaded different regions of its fingers in different ways,” said Samar Syeda, lead author of the study, in the press release.

The loading pattern shown in H. naledi is typical of a very specific type of grip still used today – the crimp grip. Crimp grips are characterized by using the tips of your fingers to grip onto a surface, much like modern-day rock climbers. This loading pattern, combined with H. naledi’s unusually curved finger bones, all but confirms that it used its hand for locomotive purposes.

Knowing that H. naledi, the younger of the two fossils, likely used its hands and fingers to propel itself while walking or running shows that ancient humans evolved at different paces, based on factors like their environment that would dictate how they needed to use their hands to collect food, use tools, and even move.

Read More: Were These 335,000-Year-Old Hominins The First to Bury Their Dead?

Article Sources

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As the marketing coordinator at Discover Magazine, Stephanie Edwards interacts with readers across Discover’s social media channels and writes digital content. Offline, she is a contract lecturer in English & Cultural Studies at Lakehead University, teaching courses on everything from professional communication to Taylor Swift, and received her graduate degrees in the same department from McMaster University. You can find more of her science writing in Lab Manager and her short fiction in anthologies and literary magazine across the horror genre.