Alzheimer’s disease may have evolved alongside human intelligence, researchers report. The study finds evidence that 50,000 to 200,000 years ago, natural selection drove changes in six genes involved in brain development. This may have helped to increase the connectivity of neurons, making modern humans smarter as they evolved from their hominin ancestors.
That new intellectual capacity was not without cost: the same genes are implicated in Alzheimer's disease. Kun Tang, a population geneticist at the Shanghai Institutes for Biological Sciences in China who led the research, speculates that the memory disorder developed as ageing brains struggled with new metabolic demands imposed by increasing intelligence. Humans are the only species known to develop Alzheimer's; the disease is absent even in closely related primate species such as chimpanzees.