Figure 1.

(a) The East African Rift Valley lake variability shown as the number of basins containing deep or shallow lakes. Lake basin occupation was calculated by collating the published geological evidence for the appearance of either deep ephemeral or shallow alkaline lakes in seven major basins (see §2). (b) East African hominin species diversity over time, which was calculated every 100 kyr interval using first (FAD) and last appearance dates (LAD) from the literature [7]. (c) Hominin brain capacity estimates for Africa and for Africa and Eurasia combined. Hominin specimen dates and brain size estimates were taken from Shultz et al. [7]. Homo erectus and H. ergaster were treated as a ‘super-species’ referred to in the figure key as Homo erectus (sensu lato). (d) The age range for key hominin species from Shultz et al. [7]. Hominin dispersal dates were estimated by FAD of hominin specimens outside the East African Rift System and are shown by the pink bars labelled ‘D’ (arrows show out of Africa, dotted within Africa only); however, it is stressed that these are liable to large dating errors and can change significantly with new discoveries. (Online version in colour.)