It seems plausible to me that the season you are born in (and thus, the season of your gestation) would have an effect. Especially in more dramatic climes, and

It seems plausible to me that the season you are born in (and thus, the season of your gestation) would have an effect. Especially in more dramatic climes, and in times previous to refrigeration, rapid transport of food, climate control. Different foods and vitamins would be available, which do have an effect. There could also be a markedly different social atmosphere in different seasons, lazy summer, forboding autumn, austere winter, hopeful spring. Thus, it wouldn't be 12 divisions, but perhaps 4 or so (and rotated 180 in the southern hemisphere). And possibly not apparent in modern society. EDIT (goodness, downvote?) some studies: intelligence correlation (http://www.thaindian.com/newsportal/health/people-born-in-spring-are-brainier-how-seasons-of-birth-influence-our-personalities_1007485.html http://www.thaindian.com/newsportal/health/people-born-in-sp...) ----- anorexia correlation http://www.independent.co.uk/life-style/health-and-families/health-news/people-born-in-spring-are-more-likely-to-become-anorexic-2275782.html http://www.independent.co.uk/life-style/health-and-families/...