The Genetic Correlation strikes again

How the ‘Black Death’ Left Its Genetic Mark on Future Generations:

They found DNA in the skeletons of 198 Danes who lived between 850 and 1800. Mutations in immune genes also rapidly spread in Denmark after the Black Death, they found. When the scientists lined up the mutations from the London and Denmark samples, they found four that had spread in both populations. These four mutations spread so quickly in London and Denmark that they must have provided an impressive protection against the plague.

The researchers found that carrying two protective versions of a gene called ERAP2, for example, made people 40 percent likelier to survive the Black Death — the largest evolutionary advantage ever found in humans, Dr. Barreiro said.

Most genetic variants have multiple effects. This is pleiotropy. And with many polygenic traits that means that there are correlations across traits impacted by how the genes underpinning them vary. I believe that many disease risks are probably just the outcome of evolutionary pressures in other directions; adapt fast to disease 1 and you become more susceptible for less serious disease 2. Over time in a stable environment, you expect evolution to “smooth out” the rough edges of the evolutionary process through modifier genes, but that can take a while. I think it’s possible the environment (pathogens) just evolve too fast for us ever to really be “in equilibrium” and get ride of the deleterious side effects, as we stay one step ahead of disease.