Lowly Origin offers a biogeographic overview of hominin evolution, with original insights for what may have happened during the split of chimp-human lineages. Thus, it has a strong focus on explaining the functional origins of bipedalism among the very first hominins. Kingdon’s ideas are inspired by the terrestrial squat-feeding hypothesis (Jolly, 1970). In this earlier model, delicate foraging for seeds from grasses, as geladas and savannah baboons do today, allowed for a more upright posture while squatting was favoured as an early precursor behaviour for bipedal walking.
Kingdon proposed a change of scenario from the grassland setting to a forest one and also expanded seeds to a variety of other nutritional resources, including insects, crustaceans, small mammals, various kinds of vegetation, and low-hanging fruits that would be readily available on the Indian Ocean coastal forests extending continuously from Somalia all the way to South Africa. This hypothetical event might have occurred as African ape lineages become geographically isolated because of aridity cycles starting at 10.5 Ma, with maximum dry peaks at 7.8 and 6.2 Ma.
Right now there are no known coastal forests of the right age and location on the fossil record to test this. But this will soon change, google Paleo-Primate Project, Gorongosa to know more.