New analysis maps complex evolution of human body size

A new study identifies a substantial evolutionary increase in body size within the genus Homo approximately 2 to 2.5 million years ago, near the appearance of Homo rudolfensis or Homo erectus/ergaster. This finding complicates previous views that human ancestors either grew gradually larger over millions of years or experienced a sudden leap in size.

Published in the Proceedings of the National Academy of Sciences, the research from the University of Reading and the University of Oxford analyzed estimated body weights from 386 fossils spanning 21 hominin species. The study reveals that while some species such as Homo floresiensis and Homo naledi remained small, others, including Homo erectus/ergaster, reached average weights of about 60 kg, comparable to many modern humans. Early hominins like Australopithecus averaged around 40 kg and were roughly child-sized.

How Body Size Varied Across Species

Lead author Dr. Jacob Gardner explained that previous studies produced conflicting conclusions because they examined different fossil subsets and used varying methods to estimate body mass. By integrating multiple fossil records, considering species relationships, and accounting for uncertainties in fossil classification, the study presents a more comprehensive view. It concludes that human body size evolution involved both gradual increases and a significant later growth spurt within Homo, while some lineages followed different paths.

Gardner stated, “The human story is not simply one of constant growth, but also of a major change that happened later, within our own genus, while other branches of the family, including some surprisingly small relatives, went their own way entirely.”

What Does the Body Size Increase Indicate?

The timing of the body size increase corresponds with broader lifestyle changes in later Homo species. These ancestors exhibited more efficient bipedal locomotion, consumed more meat, and traveled greater distances for food and habitats. Larger bodies may have supported these behaviors by enhancing mobility and dietary adaptability.

Co-author Dr. Thomas Puschel from Oxford’s School of Anthropology and Museum Ethnography noted, “Although body mass generally increased throughout our evolutionary history, the most significant shift occurred later within the genus Homo. This change coincided with broader developments in how our ancestors moved across landscapes and exploited their environments, pointing to a close relationship between body size and major ecological and behavioral transitions.”

The research challenges the traditional notion of a straightforward, continuous increase in body size among human ancestors, instead highlighting a complex evolutionary pattern involving both steady growth and abrupt changes.