Humans Evolved to Double Ancestors’ Size

Evolutionary biologists at the University of Reading in the UK determined humans have roughly doubled in size compared to their earliest ancestors over 4.5 million years. Researchers led by Jacob Gardner analyzed 386 hominin specimens from 21 groups, finding a modest initial increase in body mass of 1 to 3 kilograms per million years.

A more substantial jump occurred with the emergence of Homo erectus around 2 million years ago. Analysis of stature estimates from 4.4 million years ago to the present day revealed that most hominins were under 140 centimeters tall before 2.2 million years ago, with significant increases starting between 2 and 1.6 million years ago.

Factors driving this growth include shifts in diet, early Homo consumed more meat and cooked food, and potentially reduced sexual dimorphism, where differences in size between males and females lessened. Not all hominin groups followed this trend, however.

Species like Homo floresiensis and Homo naledi remained significantly smaller, adapting to their unique environments. Larger body size in Homo erectus may have enabled longer strides and expanded home ranges, possibly contributing to their migration out of Africa.