Evolution can be studied at two levels: macroevolution, or species evolving into new species, and microevolution, which involves smaller changes within a species over time. Macroevolution is evident in the fossil record, but microevolution is much trickier to detect. Two cave sites in South Africa, Drimolen and Swartkrans, contain fossils of Paranthropus robustus, an extinct human relative, spanning hundreds of thousands of years.

A fossil cranium recently found at Drimolen helps to show evolutionary change within this species between the sites. The older fossils from Drimolen are noticeably different from the later ones from Swartkrans, yet both are clearly fossils of the same species. These microevolutionary changes help shape our understanding of how human ancestors and relatives evolved.

Published online in the journal Nature Ecology & Evolution November 9, 2020, by Martin and colleagues, and in print in January 2021.