Agreed. I'm a non-secretor and I've benefited from not getting a norovirus when I really ought to have. But if such a valuable trait hasn't reached fixation i

Agreed. I'm a non-secretor and I've benefited from not getting a norovirus when I really ought to have. But if such a valuable trait hasn't reached fixation in the population there's bound to be a reason. It also has a variety of effects on susceptibility to other diseases, some positive, some negative. https://www.snpedia.com/index.php/Rs601338 https://www.snpedia.com/index.php/Rs601338