Human intelligence progressively diminishing: study

Researchers from Stanford University claim the intricate web of genes which endows us with our brain power is particularly vulnerable to mutations - and these mutations are not being selected against our modern society because we no longer need intelligence to survive.

However, we shouldn't lose any sleep over our diminishing brain power - as by the time it becomes a real problem - technology will have found a solution making natural selection obsolete, the 'Daily mail' reported.

"The development of our intellectual abilities and the optimisation of thousands of intelligence genes probably occurred in relatively non-verbal, dispersed groups of peoples before our ancestors emerged from Africa," said Dr Gerald Crabtree, lead author.

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.

It was downhill from there on in as, from that point, it's likely that we began to slowly lose ground, researchers claim.

According to researchers, with the development of agriculture, came urbanisation, 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 2,000 to 5,000 genes are required for intellectual ability, Crabtree estimates that within 3,000 years - about 120 generations - we have all sustained two or more mutations harmful to our intellectual or emotional stability.

Recent findings from neuroscience suggest that genes involved in brain function are uniquely susceptible to mutations, the report said.

Crabtree argues that the combination of less selective pressure and the large number of easily affected genes is eroding our intellectual and emotional capabilities.

The study was published in Cell Press journal Trends in Genetics.