[Reading Science] Unveiling the Secret of 'Upright Walking,' the Key to Human Evolution

University of Texas Research Team
Compares X-ray Images with Genomic Maps
Identifies Regions Related to Human Bipedal Evolution

Humans are the only primates that walk exclusively on two legs. As a result, they have evolved with long legs, short arms, and small hips. But why did only humans develop such a unique body structure? Recently, scientists analyzed human genes to uncover the secret behind this distinctive skeletal evolution.

Human skeleton. Reference image.

A research team from the University of Texas in the United States announced on the 21st that they completed a genomic map related to human skeletal evolution by analyzing genome maps and full-body X-ray data obtained from the UK Biobank, which collects genetic and health information of British citizens. The team's paper was published in the international journal Nature on the 19th (local time).

The researchers collected data from about 31,000 individuals to accurately measure bone lengths and compared these measurements with the genomic map. As a result, they identified 145 genomic regions associated with changes in human skeletal proportions. Many of these regions were already known to play roles in skeletal development. Forty-five of these overlapped with single protein-coding genes. Additionally, 32 regions were previously identified in mouse experiments as involved in abnormal skeletal formation when bones were fractured, and four regions were linked to rare human skeletal diseases.

The team further examined various skeletal ratios of the participants and analyzed them alongside the genomic map. They measured ratios such as hip width to shoulder width, forearm length to height, torso length to leg length, and limb length to torso length, comparing these with the genomic map. The results showed that these skeletal ratios were associated with individual genomic regions, suggesting that the development of such skeletal features is regulated by distinct genetic programs unique to each person.

Notably, having longer legs than arms is the most prominent feature of bipedalism in humans. The researchers confirmed that the genomic regions responsible for this skeletal structure in humans evolved differently from similar regions in other primates. This means that during evolution, humans uniquely selected these changes, resulting in the long legs and short arms skeletal structure and enabling upright walking.

They also found evidence supporting the existing hypothesis that early humans chose bipedalism to adapt to hot climates. By analyzing metabolic rate and body mass data, they confirmed that longer leg length improves the body's heat dissipation function to maintain coolness. The team also succeeded in identifying genomic regions related to hip and knee arthritis, leg length discrepancies, and pelvic size.

Professor Bao Xia, a geneticist at Harvard University, stated, "Further research is needed to identify the specific genomic elements causing each detailed phenomenon."