Homo erectus was sexually dimorphic: the males were bigger than females, scientists hypothesize, based on exactly two partial braincases discovered in Gona, Ethiopia. In addition, as these skulls were associated with both crude "Mode 1" and relatively complex stone "Mode 2" tools, they also deduce that this archaic species may have been more flexible in its tool use than had been supposed.
The crania were both discovered in Gona, the Afar region of Ethiopia, but the two erectuses lived very far apart, temporally speaking. One has been dated to 1.26 million years ago and the other to 1.6 to 1.5 million years ago, report Sileshi Semaw of the Spanish National Research Center for Human Evolution and colleagues in Science Advances.
In other words, the difference in time between them is roughly the same as the entire evolution of anatomically modern humans, which is now thought to have begun at least 300,000 years ago.
For its part, Homo erectus is believed to have evolved around 2 million years ago in Africa, and to have headed to Eurasia about 1.9 million years ago. Once there they split further into various hominin species, until eventually all went extinct. We do not know if Homo erectus is directly ancestral to us; our own evolution is a knotty conundrum. In any case, some also stayed in Africa, including in Ethiopia.
To be or not to be erectus
It has become increasingly clear that various hominin species coexisted in both Africa and Eurasia, until around 30,000 years ago. Which begs the question, given the scantiness of the remains, how confident are they in identifying these two as Homo erectus?
Reconstruction of Homo erectusfrantic00 / Shutterstock.com
“The larger seems fairly straightforward: the various shape indices of the skull (including the brow ridges) are classic H. erectus,” co-author Prof. Michael Rogers of Southern Connecticut State University tells Haaretz. “The smaller cranium is more open to interpretation, but again the overall shape and projecting brow ridges look most like H. erectus, in our opinion.”