How humans evolved to be twice as big as our ancestors
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- Jacob Gardner at the University of Reading, lead author of a PNAS study published June 22, analyzed 386 specimens from 21 hominin groups dating 4.5 million to 30,000 years ago, identifying two trends: a gradual 1–3 kg increase per million years and a "big jump" around the appearance of Homo erectus ~2 million years ago
- Average body mass nearly doubled across hominin evolution — from 40 kg in Ardipithecus and Australopithecus, to 45 kg in Homo habilis, 60 kg in Homo erectus, and 75 kg in prehistoric Homo sapiens
- Height climbed in step with mass: a 2017 Royal Society Open Science study by Manuel Will at the University of Tübingen found hominins under 140 cm before 2.2 million years ago, with some individuals exceeding 170 cm by 1.6 million years ago and such heights only becoming commonplace around 500,000 years ago
- Sexual dimorphism shrank markedly — Australopithecus males reached 170 cm while females stood as little as 105 cm with larger canines, but early Homo males and females grew more alike in stature, likely contributing to the overall size increase
- Dietary shifts fueled the growth: early Homo ate more meat than Australopithecus, and Gardner notes the earliest evidence of cooking appears in Homo erectus — extracting more calories per food source and possibly enabling the brain expansion that followed
- Not every hominin lineage got bigger: Homo floresiensis on the Indonesian island of Flores topped out near 100 cm until 50,000 years ago, while Homo naledi in South Africa stayed under 140 cm between 335,000 and 236,000 years ago, illustrating independent evolutionary trajectories
- Larger bodies may explain the first migration out of Africa: Gardner argues Homo erectus's longer legs and bigger home ranges help account for why they reached Java, when earlier hominins never left the continent
Why it matters: The fossil record shows human body size wasn't a gradual climb but hinged on a pivotal jump with Homo erectus roughly 2 million years ago — the same species carrying the earliest cooking evidence. That dietary shift, alongside shrinking sexual dimorphism, coincided with brain expansion and the first hominin migrations out of Africa to Java, suggesting body size, cognition, and geographic range were tightly linked in our evolutionary origins.
