*Geek Box: A ‘Shore-Based Perspective’ of Evolution
This predominant role of DHA in the brain has generated a “shore-based perspective” of human evolution, theorising that early Sapien migration and the process of encephalisation [the growth of the brain] occurred along coastal regions with access to direct food sources of DHA, in particular fish.
Stable isotope analysis of bones of early Sapiens have indicated that marine protein sources constituted significant proportions of daily energy in the human diet. Anthropological evidence for the expansion of the genus Homo from the African rift valley suggests a migration along coastal and inland watercourses, provided access to both marine and freshwater sources of fish, and in particular long-chain omega-3 fatty acids.
The evidence suggests that the consistent access to such food sources coincided with the period of exponential encephalisation, preceding the rapid development of language, complex reasoning, and problem solving cognitive capacities associated with the prefrontal cortex. Relative to other mammalian species, and indeed our primate cousins, the human brain is disproportionately large compared to body size.
A number of lines of nutritional evidence support the anthropological research. First, other mammals with high levels of other polyunsaturated fats in membranes, but without a direct dietary source of preformed DHA, did not develop large brains, indicating a foundational need for preformed DHA in the early modern human diet. Secondly, humans lost the full activity of the delta-6-desaturase enzyme responsible for converting ALA to EPA and ultimately to DHA. While it is highly active in neonatal periods, in adulthood there is very little conversion of ALA through to DHA, which again suggests a direct source of preformed DHA as a foundational dietary characteristic associated with human encephalisation.
While the Paleo narrative fantasies have often focused on our cavemen forebears huddled around the slain wooly mammoth, the reality is that the cost of obtaining land mammals as prey may have been quite high. Shore-based evolution has more anthropological, and nutritional, support, given the ease of access and low risk of obtaining freshwater and coastal marine sources, which are energy dense.