Deflationary Evolution? (MedicalExpress via Naked Capitalism)

Study suggests humans are slowly but surely losing intellectual and emotional abilities 

November 12, 2012 

Human intelligence and behavior require optimal functioning of a large number of genes, which requires enormous evolutionary pressures to maintain. A provocative hypothesis published in a recent set of Science and Society pieces published in the Cell Press journal Trends in Genetics suggests that we are losing our intellectual and emotional capabilities because the intricate web of genes endowing us with our brain power is particularly susceptible to mutations and that these mutations are not being selected against in our modern society. 

 "The development of our intellectual abilities and the optimization of thousands of intelligence genes probably occurred in relatively non-verbal, dispersed groups of peoples before our ancestors emerged from Africa," says the papers' author, Dr. Gerald Crabtree, of Stanford University. In this environment, intelligence was critical for survival, and there was likely to be immense selective pressure acting on the genes required for intellectual development, leading to a peak in human intelligence. From that point, it's likely that we began to slowly lose ground. With the development of agriculture, came urbanization, which may have weakened the power of selection to weed out mutations leading to intellectual disabilities. Based on calculations of the frequency with which deleterious mutations appear in the human genome and the assumption that 2000 to 5000 genes are required for intellectual ability, Dr. Crabtree estimates that within 3000 years (about 120 generations) we have all sustained two or more mutations harmful to our intellectual or emotional stability. Moreover, recent findings from neuroscience suggest that genes involved in brain function are uniquely susceptible to mutations. Dr. Crabtree argues that the combination of less selective pressure and the large number of easily affected genes is eroding our intellectual and emotional capabilities.

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