Modern humans have evolved with a staple source of preformed docosahexaenoic acid (DHA) in the diet. An important turning point in human evolution was the discovery of high-quality, easily digested nutrients from coastal seafood and inland freshwater sources. Multi-generational exploitation of seafood by shore-based dwellers coincided with the rapid expansion of grey matter in the cerebral cortex, which characterizes the modern human brain. The DHA molecule has unique structural properties that appear to provide optimal conditions for a wide range of cell membrane functions. This has particular implications for grey matter, which is membrane-rich tissue. An important metabolic role for DHA has recently been identified as the precursor for resolvins and protectins. This is from the work of Nicolas Bazan. The rudimentary source of DHA is marine algae; therefore it is found concentrated in fish and marine oils. Humans are not designed to eat marine algae. They contain DHA in the SN-2 position. When the marine food chain consumes the algae they convert it to the SN-2 position so that mammals can utilize this is in their CNS and PNS. This is one reason why ALA conversion is poor in humans. They have relied on the marine food chain for 2-4 million years as they went brain evolution from chimp to silly taking monkey: humans.
Unlike the photosynthetic cells in algae and higher plants, mammalian cells lack the specific enzymes required for the de novo synthesis of alpha-linolenic acid (ALA), the precursor for all omega-3 fatty acid syntheses. Endogenous synthesis of DHA from ALA in humans is much lower and more limited than previously assumed. The excessive consumption of omega-6 fatty acids (seed oils) in the modern Western diet further displaces DHA from membrane phospholipids. An emerging body of research is exploring a unique role for DHA in neurodevelopment and the prevention of neuropsychiatric and neurodegenerative disorders. DHA is increasingly being added back into the food supply as fish oil or algal oil supplementation. This is a suboptimal strategy in the fish oil case due to the sensitivity of light and temperature of DHA outside of the marine food tissue. And algal oil is heavily loaded with the unusable SN-1 and SN-3 position.
Interestingly, the exploitation of food from aquatic and marine sources coincided with a rise in a more elaborate enrichment in material cultures, such as personal ornamentation, decoration of burials, pottery figurines, and knotted textiles. Richards et al. concluded that the inclusion of seafood is likely to have “…rendered humans more resilient to natural pressures and the increasingly packed social environments of Late Pleistocene Europe”
Crawford, Broadhurst and Cunnane et al. move the argument forward by linking diet with brain size; specifically, the expansion of the diet to include seafood with the expansion of grey matter in the cerebral cortex. They note that over 3 million years of evolution had little effect on the brain capacity of Australopithecus spp.
Conversely, brain capacity doubled in the million years between Homo erectus and Homo sapiens. In fact, they observed that the encephalization growth rate was exponential in the past 200,000 years. When you add in the fact that DHA has never been replaced one time in 650 million years of evolution you can only be left with one thought: If evolution records adaptation as most believe.......the evolution of the human neocortex relies exclusively on concentration this one fat.

https://www.biomolther.org/journal/view.html?uid=277&vmd=Full