Perspectives in Biology and Medicine

THE POSSIBLE ROLE OF LONG-CHAIN, OMEGA-3 FATTY ACIDS IN HUMAN BRAIN PHYLOGENY JACK G. CHAMBERLAIN* Nothing in biology makes sense except in the light of evolution.—T. Dobzhansky , Mankind Evolving (1962). Background The present era has been designated as the decade of the brain [1], and fellowships are being given for research concerned with "the probing of nature's mysteries and challenging dogma" [2]. Nothing in biology has generated more interest of late than narrative theories and outright fantasies about human origins and evolution [3-10]. Within that paradigm a great enigma still remains: namely, how the human brain tripled in size within three million years ofevolution [1 1-18] . In some ways, only emeritus professors appear to have the freedom to devote some thought to such cosmic issues of human evolution [19]. Why is that? Because, although refuted by Eccles [20], many neuroscientists still feel that human brain evolution narratives appear to be empty of facts and good only for unjustified speculation. However, the narrative approach allows for new hypotheses [3, 12]. Since brain growth determines skull shape, virtually all our understanding of brain phylogeny is based on relatively few fossils (endocasts) and related cultural artifacts (tools) [21-23] . Soft tissues don't fossilize and are lost to the geologic record. Much also has been made about hominid comparisons with extant hunter-gatherers, i.e., !Kung san, Native Australians, etc. [6, 24-26] . One of the banes in the lives of paleoneurologists is surely the lack of sufficient fossil evidence and the precise dating of the earliest tool making [23, 27-29] . Although nutrition and foraging no doubt played a selective role in brain evolution, they have received less attention than, *1534 Scenic Avenue, Berkeley, CA 94708.© 1996 The University of Chicago. All rights reserved. 0031-592/96/3901-0946101.00 436 Jack G. Chamberlain ¦ Fatty Acids in Human Brain Phylogeny say, speech, language, or tool making [23, 30-34] . Although protein, carbohydrate , and energy sources for brain expansion have been surmised, little is known about the micronutrition of early humans [10, 12, 35-42]. Our recent fatty acid analyses offood sources ofextant primates, showing relatively high polyunsaturated fatty acid (PUFA) intake, provides a clue perhaps to dietary elements eaten by early humans [43-46]. If much of our knowledge regarding human origins and brain evolution is based on bones and stones and extant nonurbanized peoples, then we also may have learned something from lipid analyses of extant food sources, since many edible plants have been around for at least 30 million years (e.g., Ficus). I present here an additional key element underlying brain phylogeny: animal fat, particularly the possible role ofvital, highly unsaturated, long-chain fatty acids (HUFA). Brain in General As multicellular organisms evolved, the needed integrative function of the nervous system became localized more and more at the head or leading end of the animal. In fact, in the Arthropoda, the most numerous phylum, and in some worms, the brain evolved around the anterior digestive tract; these animals had the evolutionary choice to either eat a lot and stay dumb or become smart but starve to death—an evolutionary dead end. Likewise, in Australian marsupials the adult brain lacks a corpus callosum [20, 47]. It is within the Eutherian (placental) mammals that brain development reaches its zenith, although it appears that it will take molecular methods to resolve the many phylogenetic and cladistic quandries in this taxon; appearances can deceive [48-52]. Obviously, various animal groups have become quite "intelligent," even to the point of making tools and communicating within their respective niches; there are various kinds of ' 'intelligence " [53-57]. Modern humans have large brains relative to body size, but the tree shrew, house mouse, porpoise, and squirrel monkey do also [6] . But then again humans are bipedal; animals no doubt eventually think better when they stand upright for a million years. Over millions of years, plants and most animals have evolved the ability to elongate and desaturate dietary fatty acids so as to supply their cells with HUFA [58]. Such compounds of 20 to 24 carbons with four to six double bonds are necessary for membrane formation, prostaglandin production, development and...