Evolution of the Human Brain: the key roles of DHA (omega-3 fatty acid) and Δ6-desaturase gene

Abstract

The process of hominization involves an increase in brain size. The development of hominids’ cognitive capital up to the emergence ofHomo sapienswas due to interactive, iterative, and integrative coevolution, allowing positive selection. Although this depends on many factors, in this position paper we show three categories that stand out: gene mutations, food resources, and cognitive and behavioral stimulation.Australopithecusbenefited both from the inactivation of theGULOanduricasegenes and from bipedalism causing the cognitive capital of theHomo genus to develop advantageously. This evolution depended on two factors. Firstly, a triggering factor: gradual climate change.Homostarted to regularly consume meat in addition to plants and insects. Secondly, a stimulating factor: mutations in theFADS2gene, which encodes Δ6-desaturase; a key enzyme for the synthesis of DHA and sapienic acid. The polymorphism of this gene appears to have been essential in allowing theHomo genus to adapt to its food, and for its evolution. It provides an undeniable advantage in terms of the productivity of fat synthesis (DHA), and may partly explain positive selection. With the advent of cooking and new mutations producing even moreFADS2, the brain reached its maximum size inHomo neanderthalensis, in a food ecosystem that provided favorable quantities of α-Linolenic acid and DHA. However, the Würm glaciation upset this equilibrium, revealing its fragility as regards to the brain and fertility.Homo sapiens, benefiting from new variants of theFADS2gene, were able to adapt to this harsh environment, whereas Neanderthal man was unable to do so and became extinct.