The bigger brains that evolved with early modern humans may have come with an unfortunate side effect—Alzheimer’s disease. A new study shows that this memory-robbing disease may have evolved alongside human intelligence, a finding that could eventually help us eradicate it.
Using a new technique, a team of scientists led by Kun Tang, a population geneticist at the Shanghai Institute for Biological Sciences, searched for genetic variation among 90 people of African, Asian, or European ancestry.
Here’s Nala Rogers, writing for Nature:
The analysis was tricky, because the two effects can mimic each other. To control for the effects of population changes ― thereby isolating the signatures of natural selection — the researchers estimated how population sizes changed over time. Then they identified genome segments that did not match up with the population history, revealing the DNA stretches that were most likely shaped by selection.
The team was able to identify and trace instances of natural selection as far back as 500,000 years ago. Modern humans came onto the scene about 200,000 years ago, so this is the first time scientists have been able to get a glimpse of different genes as anatomically modern humans evolved. They found that six genes drove evolution in brain development between 200,000 and 50,000 years ago. Tang speculates that Alzheimer’s is a byproduct of an intelligent, energy-hungry brain paired with an aging metabolism.
Perhaps even more promising is the approach Tang and his colleagues used, which may be applicable in other genetic contexts, though researchers still have to test it in other situations.