Humans doubled body mass over 4.5 million years
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- Jacob Gardner of the University of Reading led a PNAS study published 22 June that compiled body mass estimates for 386 specimens across 21 hominin groups, finding average mass rose from 40 kg in early hominins like Ardipithecus and Australopithecus to 75 kg in prehistoric Homo sapiens
- The team identified two trends: a gradual 1-3 kg increase per million years (explaining roughly a third of the total change) and a "big jump" around the appearance of Homo erectus about 2 million years ago, which averaged 60 kg and was the first hominin known to migrate out of Africa
- A separate 2017 Royal Society Open Science study led by Manuel Will at the University of Tübingen tracked stature across the same period, finding most hominins stood under 140 cm before 2.2 million years ago, with individuals exceeding 170 cm first appearing around 1.6 million years ago
- Gardner attributes the size surge partly to dietary shifts: more meat eating plus the earliest evidence of cooking appearing in Homo erectus, which unlocked more calories and may have also fueled brain expansion
- Reduced sexual dimorphism likely contributed too: early hominins showed male-female size gaps comparable to chimpanzees, while early Homo males and females converged in body size
- Not every hominin got bigger - Homo floresiensis on Indonesia stayed around 100 cm tall until 50,000 years ago, and Homo naledi in South Africa (335,000-236,000 years ago) topped out near 140 cm, showing each group followed its own evolutionary path
Why it matters: The body-size shift reframes the standard brain-centric narrative of human evolution: bigger frames demanded more calories, cooking helped deliver them, and the extra nutrition may have simultaneously powered brain growth. For paleoanthropology, the study gives a sharper timeline and a fresh puzzle - the sudden size jump around Homo erectus may help explain why that species was the first to leave Africa, something earlier hominins never did.
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