MaHuman 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.
But not to worry. The loss is quite
slow, and judging by society's rapid pace of discovery and
advancement, future technologies are bound to reveal solutions to
the problem. "I think we will know each of the millions of human
mutations that can compromise our intellectual function and how each
of these mutations interact with each other and other processes as
well as environmental influences," says Dr. Crabtree. "At that time,
we may be able to magically correct any mutation that has occurred
in all cells of any organism at any developmental stage. Thus, the
brutish process of natural selection will be unnecessary."
More information: Crabtree et al.: "Our
fragile intellect. Part I." Trends in Genetics Crabtree et al.: "Our
fragile intellect. Part II." Trends in Genetics
http://www.sciencedirect.com/science/article/pii/S0168952512001588
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