First humans emerged in Africa 2.8 million years ago during sudden climate change

The first humans lived in a dry and grassy landscape very like today's Serengeti in East Africa, a wide-scale study of the region has revealed.

East Africa dried out around three million years ago and forests turned into grassy plains. The earliest known example of the Homo genus – at 2.8 million years old – thrived through this change while earlier species, such as that of the famous "Lucy" fossil, died out.

Lucy was discovered in 1974 in Hadar, in the Afar region of Ethiopia. The ancient Homo fossil was discovered in 2013, just 30km away from this site in the lower Awash Valley.

Our early ancestors lived in a landscape that was very like today's dry grassy plains of East Africa. The changing climate didn't have a big impact on the prey that they ate, according to a study in the journal Nature Ecology and Evolution. The earliest humans ate similar food to Lucy, an Australopithecus afarensis, the authors found.

"We weren't necessarily surprised that the diet of early Homo was similar to Australopithecus," said study author Chris Campisano of the Arizona State University in a statement. "But we were surprised that its diet didn't change when those of all the other animals on the landscape did."

The researchers analysed the teeth of the 2.8 million-year-old human ancestor, as well as the large animals that roamed the plain in the same period. Data from animals grazing across the lower Awash Valley and nearby regions have been used to piece together a climate history from 3.5 to one million years ago.

Analysis of bones of wildebeest, antelope, ancient horses, giraffes and prehistoric elephants revealed that the climate change in East Africa at this time was significant, changing the diets of many species.

"Although Lucy's species persisted through many environmental changes in the Hadar sequence, it seems the species was unable to persist as really open environments spread in the Afar during the late Pliocene," said study author John Rowan, also of Arizona State University.

This fundamental shift in climate could have been the cause for the earliest human species to arise, the authors speculate.

"It is possible that late Pliocene environmental change in the lower Awash Valley played a role in the emergence of early Homo from Australopithecus, but the evidence is too scant at present to draw such causal links," they write in the paper.

The next stages of the research will be to create climate records through analysing animal remains to see how and when the grasslands spread through East Africa, and how the earliest Homo managed to fit in to the new, arid landscape.