Tony Wright gives a brief introduction to his symbiotic theory of human evolution presented in 'Left in the Dark'. He describes how the limitations of cerebral dominance (left hemisphere in charge) affect our capacity to see the problem. He then describes our symbiotic relationship with plants and how this is a key factor in our cognitive capacity.
"A lot of our complex traits have been shaped and sculpted by the chemistry of the plants, it's not logged in our DNA, it's not something we can do so you end up with a situation where our consciousness system, our neural system and much of our physiology becomes entirely dependent on the plants particularly fruit."
Separated from our natural environment, the non-seasonal tropics, our unique traits which are to do with this unique symbiosis, including cognitive function, dwindle.
Fruit compounds such as flavonoids have a triple effect on the way our DNA is transcribed or read. They affect transcription directly, they also affect the steroids which are the major players in terms of transcription and they affect the hormonal output of the pineal principally pinoline and melatonin which also affect DNA transcription. We are not talking about subtle changes here, with changes to the neural system, we are talking about the potential to effectively experience a different sense of self.
Forging a relationship with the hormone rich sex organs of plants, as if in the uterus of the plants, led to less differentiation and longer windows of development, less differentiation meant more fluid neocortex and less difference between the brains of men and women. Take that away by losing our relationship with the fruit forest and we revert to a simpler mammalian type - good at survival but it's the symbiosis with the humans and the fruit chemistry that produces the amazing neural system with all its traits.