Ancient hominins had small brains like apes, but longer childhoods like humans

Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the hominin species Australopithecus afarensis more than 3 million years ago, we scanned eight fossil crania using conventional and synchrotron computed tomography. We inferred key features of brain organization from endocranial imprints and explored the pattern of brain growth by combining new endocranial volume estimates with narrow age at death estimates for two infants. Contrary to previous claims, sulcal imprints reveal an ape-like brain organization and no features derived toward humans. A comparison of infant to adult endocranial volumes indicates protracted brain growth in A. afarensis, likely critical for the evolution of a long period of childhood learning in hominins.

Media Mentions

Science Magazine | ‘Lucy’s baby’ suggests famed human ancestor had a primitive brain. April 1, 2020 [online article]

The Conversation | Baby steps: this ancient skull is helping us trace the path that led to modern childhood. April 1. 2020 [online article]

ScienceNews | Lucy’s species heralded the rise of long childhoods in hominids. April 1. 2020 [online article]

UChicago Medicine | Ancient hominins had small brains like apes, but longer childhoods like humans. April 1. 2020 [online article]

Gizmodo | Lucy’s Brain Was Part Ape, Part Human. April 2, 2020 [online article]

The Times | Big-brained ancient ape was in no hurry to grow up. April 2. 2020   [online article]

United Press International |Ancient human relative Lucy’s brain was surprisingly ape-like. April 1, 2020 [online article]

Cosmos |More clues to the story of our past. April 2, 2020 [online article]