Fertility and the Plough. Nathan Nunn, 2011, Paper. "Recent studies provide evidence that a significant portion of the cross-country variation in female labor participation and fertility can be explained by cultural norms. In a recent paper, we examine the historical origins of these cultural differences (see Alesina, Giuliano, and Nunn 2010). We test the long-standing hypothesis, first developed by Ester Boserup (1970), that different attitudes about gender roles evolved because of differences in the form of agriculture traditionally practiced. In societies with shifting cultivation, agriculture is labor intensive, cultivation uses a hoe or a digging stick, and women actively participate..." Link