Brain Rules vs. 10,000 Year Explosion

These two books fell into my hands at the same time. Reading them concurrently was quite interesting.  They paint starkly contrasting pictures of the human brain.

Brain Rules (pgs. 4-5) says the brain’s formative period, evolutionarily speaking, was on the Serengeti:

The brain appears to be designed to solve problems related to surviving in an unstable outdoor environment, and to do so in nearly constant motion.

10kYE (pgs. 74-75), in contrast, says:

Many [alleles] are very recent: the rate of origination appears at about 5,000 years ago in the European and Chinese samples, and at about 8,500 years ago in the African sample. […]  Many involve changes in metabolism and digestion, in defenses against infectious disease, in reproduction, in DNA repair, or in the central nervous system [emphasis mine – CF].

10kYE (pg. 98) later elaborates on this idea:

The most interesting kind of genetic changes are those that affect human personality and cognition, and the evidence is good that such changes have indeed occurred. […] Several of the new alleles have effects on serotonin, a neurotransmitter involved in the regulation of mood and emotion. […] And there are new versions of genes that play a role in brain development: genes that affect axon growth, synapse formation, formation of the layers of the cerebral cortex, and overall brain growth.

Brain Rules (pg. 81) says “Universally experienced stimuli…follow strict Darwinian lines of threats and energy resources.”

10kYE (pg. 112) says:

The polymorphism [the7R allele of the DRD4 {Dopamine Receptor D4} gene, associated with Attention-Deficit/Hyperactivity Disorder] is found at varying but significant levels in many parts of the world, but is almost totally absent from East Asia….It is possible that individuals bearing these alleles were selected against because of cultural patterns in China.

Brain Rules (pg. 10) describes our evolutionary history this way:

When our bountiful rain forests began to shrink, collapsing the local food supply, we were forced to wander around an increasingly dry landscape looking for more trees we could scamper up to dine.  As the climate got more arid, these wet botanical vending machines disappeared altogether.  Instead of moving up and down complex arboreal environments in three dimensions, which required a lot of dexterity, we began walking back and forth across arid savannahs in two dimensions, which required a lot of stamina.

10kYE devotes an entire chapter, titled “Medieval evolution: How the Ashkenazi Jews Got Their Smarts”, to informed speculation that Ashkenazi Jewish brains have profoundly evolved in the last 1000 years.

Our brains’ evolution either stopped when we were hunter-gatherers and has had no time to adapt to the hugely different set of risks and stimuli provided by modern society, or it didn’t.  Cochran and Harpending admit some of their specific examples are speculative and unproven, but in general, they are solidly convinced that humans and human nervous systems have been evolving rapidly in the last 10,000 years. In contrast, Brain Rules is rooted to the idea that the cubicles of our modern workplace or the desks of our modern class rooms are “anti-brain”, because our brain evolved in hunter-gatherers who lived in open grasslands. The tension between these two core ideas seems inescapable.

I am no neuroscientist; I am just an outsider looking in. But my sense is that Harpending and Cochran are challenging neuroscience orthodoxy, and that Medina’s book is, scientifically, a distillation of current mainstream thought. It will be interesting to see how well the ideas of Cochran and Harpending catch on in coming years.


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