Human beings exhibit considerable variations in behavior and culture because of adaptation to local environments, random drift and so on. The average age at which women have their first child varies across culture. Evolutionary theory predicts that the age of onset of female reproduction should be sensitive to variation in mortality rates, so that the variations in reproductive timing are expected to be related with the variations in local ecology among societies. Previous studies showed that age at first marriage and family size varied among prefectures in Japan because of local adaptation.

In the present study, using demographic data, we show the temporal change of the latitude cline in the average marriage age. Besides, we also show the temporal change of geographical clines in other factors influencing environmental quality and life history strategies. Based on the results, we discuss the relationship between cultural transmission and ecological adaptation.