Wiring the Brain

This is a modified version of a letter published in Trends in Genetics: Kevin J. Mitchell (2012). Genetic entropy and the human intellect. Trends in Genetics, 14 th December 2012. Two articles by Gerald Crabtree float the notion that we, as a species, are gradually declining in average intellect, due to the accumulation of mutations that deleteriously affect brain development or function [ 1 , 2 ] . The observations that prompted this view seem to be: (i) intellectual disability can be caused by mutations in any one of a very large number of genes, and: (ii) de novo mutations arise at a low but steady rate in every new egg or sperm. He further proposes that: (iii) genes involved in brain development or function are especially vulnerable to the effects of such mutations. Considered in isolation, these could reasonably lead to the conclusion that mutations reducing intelligence must be constantly accumulating in the human gene pool. Thankfully, these f

An enduring question in philosophy and neuroscience is whether any individual’s subjective perceptual experiences are the same as those of other people. Do you experience a particular shade of red the same way I do? We can both point to something in the outside world and agree that it’s red, based on our both having learned that things causing that perceptual experience are called “red”. But whether the internal subjective experience of that percept is really the same is almost impossible to tell. There are some exceptions, of course, where there are clear differences between people’s perceptions. Colour blindness is the most obvious, where individuals clearly do not experience visual stimuli in the same way as non-colourblind people. This can be contrasted with the experience of people who are tetrachromatic – who can distinguish between a greater number of colours, due to expression of a fourth opsin gene variant. Conditions like face blindness and dyslexia