Earliest Olduvai hominins exploited unstable environments ~ 2 million years ago.

Rapid environmental change is a catalyst for human evolution, driving dietary innovations, habitat diversification, and dispersal. However, there is a dearth of information to assess hominin adaptions to changing physiography during key evolutionary stages such as the early Pleistocene. Here we report a multiproxy dataset from Ewass Oldupa, in the Western Plio-Pleistocene rift basin of Olduvai Gorge (now Oldupai), Tanzania, to address this lacuna and offer an ecological perspective on human adaptability two million years ago. Oldupai's earliest hominins sequentially inhabited the floodplains of sinuous channels, then river-influenced contexts, which now comprises the oldest palaeolake setting documented regionally. Early Oldowan tools reveal a homogenous technology to utilise diverse, rapidly changing environments that ranged from fern meadows to woodland mosaics, naturally burned landscapes, to lakeside woodland/palm groves as well as hyper-xeric steppes. Hominins periodically used emerging landscapes and disturbance biomes multiple times over 235,000 years, thus predating by more than 180,000 years the earliest known hominins and Oldowan industries from the Eastern side of the basin.

Testosterone and paternal care in East African foragers and pastoralists.

The 'challenge hypothesis' posits that testosterone facilitates reproductive effort (investment in male-male competition and mate-seeking) at the expense of parenting effort (investment in offspring and mates). Multiple studies, primarily in North America, have shown that men in committed relationships, fathers, or both maintain lower levels of testosterone than unpaired men. Data from non-western populations, however, show inconsistent results. We hypothesized that much of this cross-cultural variation can be attributed to differential investment in mating versus parenting effort, even among married fathers. Here, we directly test this idea by comparing two neighbouring Tanzanian groups that exhibit divergent styles of paternal involvement: Hadza foragers and Datoga pastoralists. We predicted that high levels of paternal care by Hadza fathers would be associated with decreased testosterone in comparison with non-fathers, and that no such difference between fathers and non-fathers would be evident in Datoga men, who provide minimal direct paternal care. Twenty-seven Hadza men and 80 Datoga men between the ages of 17 and 60 provided morning and afternoon saliva samples from which testosterone was assayed. Measurements in both populations confirmed these predictions, adding further support to the hypothesis that paternal care is associated with decreased testosterone production in men.