Review of “Brain Expansion in Early Hominins Predicts Carnivore Extinctions in East Africa” (2020)
Read in 2020.
Statistical comparison of possible reasons for the high extinction rate of large carnivore species in East Africa (now Ethiopia, Kenya, Tanzania), in the past four million years, as compared to an apparently static background rate of extinction among small (<21 kg) carnivores.
Among the variables surveyed (Fig. 1), we found significant support for two scenarios for this increase in extinction rate among large carnivores: either an anthropogenic impact, indicated by a correlation between extinction rate and hominin brain size; or, alternatively, an increased extinction rate driven by reduced forest cover (Fig. 2). On the other hand, we found no support for the effects of temperature, precipitation or water deficit (Fig. 2; Table S3).
Thus the near ancestors of humans were out-competing their competitors across millions of years, “as a function of more advanced behaviour and eventually more advanced tool use”, such as (hypothetically) thorny branches as weapons and kleptoparasitism, though their diet wasn’t necessarily high in meat. The authors suggest that the status of modern humans as a “hyperkeystone species” extends back into this era.
Exciting stuff for a scientific paper; an admirably clear study with the usual limitations (fairly few fossils, deriving causation from correlation through several complex computer models). A useful antidote to old culture-focused fluff like “A Non-Euclidean View of California” (1982), and to more bizarre theories like the one presented in Fantastic Fungi (2019), which is that human brains grew because humans were consuming psilocybin from mushrooms growing out of the faeces of their prey.