Tropical forest biochemistry, the driving force in human evolution
By Tony Wright
Do the universal myths of humanities fall from grace contain an accurate diagnosis relating to the onset and progression of a complex neurological condition? Were the origins of ancient religious practice an attempt to treat the symptoms of that condition and do those various practices offer specific insights into its nature? Are there any anomalies or evidence in modern neurology, psychology, consciousness research and other disciplines that would support such a scenario?
These questions have been central to my research for the last 12 years, the answer to these questions in my opinion is yes on all counts. More importantly if such a condition is proven to exist then it may be possible to both treat it and prevent its further occurrence.
The following article provides a basic introduction to a new theory that may shed light on a number of apparently unrelated mysteries.
The evolution of the large human brain remains one of biology's greatest unsolved mysteries. Primates generally have a relatively large brain to body ratio, apes, the extinct hominids and particularly humans have taken this trait to extreme. No theory to date has come close to explaining this phenomena.
Some of the key elements
- The relatively large brain to body ratio exhibited by primates generally
- The continued expansion of the brain from apes through the extinct hominids to humans.
- The rapid and accelerating expansion of the brain in the later phase of human evolution.
- The abrupt stall in neural expansion c 200,000 years ago and the subsequent shrinkage.
Associated traits that have also proved difficult to explain, i.e. retention of juvenile characteristics, fertility/menstruation, nakedness, gut morphology, fuel hungry brain, dentation etc.
Attempts to explain the large brain and other unusual traits have centred on adaptive selection i.e. identifying environmental/social pressures that may have led to such unusual physiological adaptations.
The savannah was virtually accepted as the environment that must have driven these traits though it could not account for what was already a significant mystery i.e. the relatively large ape brain that had already evolved in the forest. However without solving that unique problem a totally new one was invented, how to explain the extra large brain of the hominids. That two such clearly related and unusual phenomena would have two utterly distinct causes seems unlikely.
The savannah model has in recent times been significantly discounted, subsequent pollen analysis at famous 'savannah' hominid fossil sites has clearly indicated that the habitats were wooded or forested. In addition Dr Michael Crawford a biochemist from the Institute of Brain Chemistry and Human Nutrition at the University of North London has pointed out that there are insufficient fatty acids (specifically DHA, the brain is composed of 80% DHA) available on the savannah to grow a large brain.
Dr. Crawford and others support a coastal dwelling scenario whereby human ancestors moved from the forest to live by the coast as this environment provides an abundant supply of DHA. The implication being that the expansion of the brain was limited by the lack of a ready supply of DHA or the rate the body can convert omega 3 fatty acids to DHA and simply providing a ready source was all that was required to induce rapid expansion.
In recent correspondence with Dr Crawford I pointed out that an ape can grow a c200 cubic centimetre brain in around 8 months primarily by converting omega 3 fatty acids available in a forest diet to DHA. By simply extending the rapid growth windows a much larger brain is feasible via omega 3 conversion without recourse to additional ready made DHA. Human brain growth occurs over a much longer period than apes. Longer gestation and a very significant period of postnatal brain growth is a unique feature of human development. Breast milk contains significant amounts of DHA depending on the fatty acid composition of the diet being eaten and can be drawn from reserves laid down before pregnancy. Extending the breastfeeding period may have been an essential part of the neural expansion formula ironing out the high demand for DHA during early development.
Another contender is the aquatic ape theory, it suggests many human traits could be explained by a long period of living in a semi-aquatic environment. No mechanism is proposed to explain how the association was responsible for producing such a large brain.
The reality is that no coherent model exists and there is no consensus to explain the unique features of the primate brain particularly the apes, extinct hominids and humans.
Perhaps it is reasonable to consider that evolution of such rare traits may have required a novel mechanism to produce them. Genetic mutation and selective adaptation seems to account very well for virtually all traits in all organisms. In the case of primate/human evolution a subtle variation may have been at work alongside classic selection.
One well known anthropologist, Dr Colin Groves has suggested that the large brain may be a fortuitous consequence of neoteny (retention of juvenile features). This contradicts previous ideas where neoteny has been presumed to be a consequence of the expanding brain. In recent correspondence he stands by his proposal though he has not proposed a mechanism to account for this.
A common factor central to juvenility and brain development is our own endocrine system and the hormones it produces, particularly the sex steroids. They play a major role in governing windows of development and directly influence the structural development of the brain. In addition steroids are directly involved in the transcription of DNA, they are part of the reading mechanism dictating how the code is translated into bio-chemical structure. Anything that alters the action of steroids will inevitably alter all of the above.
I have proposed that the powerful steroid modulating chemicals that are abundant in a typical primate diet were responsible for modifying the growth and development of the brain and the window that such growth and development occurs.
The chemicals in question are particularly rich in fruit and flowers and typically inhibit the activity of sex steroids such as testosterone and estrogens. In addition they have mild to moderate neuroactive properties (Monoamine oxidase inhibitors).
Flavonoids are increasingly the subject of research in part because they demonstrate such powerful endocrine altering properties.
Any animal consuming these chemicals in quantity will be affected.
A tropical forest environment has the capacity to provide these chemicals 24/7 for evolutionary time scales.