Increased ecological resource variability during a critical transition in hominin evolution

Abstract

Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated. We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site. Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores. Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover. Interaction of these factors offers a resource-oriented hypothesis for the evolutionary success of MSA adaptations, which likely contributed to the ecological flexibility typical of Homo sapiens foragers.

Fine-grained temporal mapping of derived high-frequency variants supports the mosaic nature of the evolution of Homo sapiens

“…Our analysis highlights the importance of a temporal window between 300-500k that may well correspond to a significant behavioral shift in our lineage, corresponding to the Jebel Irhoud fossil, but also in other parts of the African continent, to increased ecological resource variability [53], and evidence of long-distance stone transport and pigment use [54]. Other aspects of our cognitive and anatomical modernity emerged much more recently, in the last 150000 years, and for these our analysis points to the relevance of gene expression regulation differences in recent human evolution, in line with [55,56,57].…”

The evolution of the human trophic level during the Pleistocene

“…The evidence of an adaptation to a highly carnivorous trophic level for H. erectus and H. sapiens , and possibly a further specialization in the acquisition of large prey, present an alternative hypothesis to the one marking human adaptive transitions toward general resource variability (Potts et al, 2020). The selection for specialization in large prey instead of dietary variability, if accepted, can provide causality to the association made by Potts et al (2018) between a decline in prey size in East Africa and the appearance of the MSA.…”

Cascading effects of elephant-human interactions in a savanna ecosystem and the implications for ecology and conservation

“…Here at 1 million BP, the fossilized remains of Elephas recki , a species twice the weight of Loxodonta africana , is surrounded by discarded stone tools and shows multiple cut marks on the bones (29). It is unclear if the disappearance of Elephas recki, which coincided with the 75% turnover of the large mammal fauna in the transition from the Lower to Middle Stone Age 500,000 to 350,000 BP, was due to climatic changes or the emergence of more sophisticated weaponry and hunting techniques or both (30). The eruption of taller grasslands following the loss of the largest species across a range of herbivore taxa at a time the climate was drying is, however, consistent with Owen-Smith’s (1987) herbivore release hypothesis explaining the growth of coarse vegetation following the extinction of megaherbivores.…”