Parallel regress

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Published: June 1, 2015 12:24 AM

Was Alzheimer’s disease a fallout of the evolution of human intelligence?

It would be one of life’s deep ironies if it turns out that the same factors that caused human intelligence to develop were also responsible for Alzheimer’s disease, a neurodegenerative condition, that eventually completely incapacitates the brain’s memory faculties. As per a report in Nature that cites a paper posted on bioRxiv, a pre-print platform for biologists to discuss their research, six genes that are held to be behind the increased connectivity of neurons in humans as compared to their hominin ancestors could also be behind Alzheimer’s.

A study at the Shanghai Institutes for Biological Sciences has found evidence that, some 50,000 to 200,000 years ago, natural selection drove the six genes to induce intelligence in humans. At the same time, Kun Tang, the lead researcher of the study, holds, Alzheimer’s developed as ageing brains struggled with new metabolic demands imposed by increasing intelligence—humans, it is worth noting, are the only species known to suffer from Alzheimer’s; not even closely-related primates like chimpanzees have it. The researchers combed modern human DNA across races for evidence of this evolution, looking for variations driven by changes in population size and natural selection. The analysis though, Nature reports, is quite tricky as the two effects often are indiscernible. The researchers isolated natural selection effects by establishing controls for the population effects by estimating population shifts over time. The genome segments that didn’t match for population history were studied to reveal changes brought about by natural selection. The method enables the study of selection events that occurred upto 500,000 years before, beats most others that can go as far back as 30,000 years. Tang and his team focussed on events some 200,000 years ago—the dawn of the modern man—to study for evolution of human intelligence and the inception of Alzheimer’s.

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