What's the Big Idea?

One of the most significant periods in human evolution occurred 1.8 million years ago. Humans adapted to fundamental environmental changes by migrating out of Africa and developing substantially greater brain capacity. 

These occurrences have been statistically linked in a study published in the journal PloS ONE

As the authors of the studies note, early human evolution "cannot be explained fully by global or continental paleoclimate records." Therefore, the study looked at regional paleoclimate conditions in Africa, specifically the appearance and disappearance of deep-freshwater lakes along the East Africa Rift valley. The authors write:

During this period, ephemeral deep-freshwater lakes appeared along the whole length of the EARS, fundamentally changing the local environment. The relationship between the local environment and hominin brain expansion is less clear. The major step-wise expansion in brain size around 1.9 Ma when Homo appeared was coeval with the occurrence of ephemeral deep lakes. Subsequent incremental increases in brain size are associated with dry periods with few if any lakes.

What's the Significance?

According to Mark Maslin, one of the authors of the study, we now have started to put together "a coherent picture of how the changing East African landscape has driven human evolution over the last ten million years." 

Read more here