Recent human ancestors may have regularly climbed trees, research suggests.
Based on analysis of fossil leg bones, scientists in England say a hominin species, believed to be either Paranthropus robustus or early Homo, regularly adopted highly flexed hip joints.
This is a posture that in other non-human apes is associated with climbing trees.
Hominins are members of the human family tree more closely related to one another than to apes.
Today, only one species of this group remains, Homo sapiens, to which everyone on Earth belongs.
The study, led by the University of Kent, analysed and compared the internal bone structures of two fossil leg bones from South Africa, discovered more than 60 years ago and believed to have belonged to a creature which lived between one and three million years ago.
For both fossils, the external shape of the bones were very similar, showing a more human-like than ape-like hip joint, suggesting they were both walking on two legs.
The researchers also examined the internal bone structure, because it remodels during life based on how individuals use their limbs.
But when they analysed the inside of the spherical head of the thigh bone, it showed they were loading their hip joints in different ways.
The study, published in Proceedings of the National Academy of Sciences, was led by Dr Leoni Georgiou, Dr Matthew Skinner and Professor Tracy Kivell at the University of Kent’s School of Anthropology and Conservation.
Dr Georgiou said: “It is very exciting to be able to reconstruct the actual behaviour of these individuals who lived millions of years ago and every time we CT scan a new fossil it is a chance to learn something new about our evolutionary history.”
Dr Skinner said: “It has been challenging to resolve debates regarding the degree to which climbing remained an important behaviour in our past.
“Evidence has been sparse, controversial and not widely accepted, and as we have shown in this study the external shape of bones can be misleading.”