aut.sagepub.com 'male disorder' (e.g. Zwaigenbaum et al., 2012). The need for females to display more severe symptomatology to receive a diagnosis of ASD may explain the apparent paradox that in clinically diagnosed samples, females may show more severe ASD traits and comorbid psychopathology than males even though the latter have a greater vulnerability to ASD (e.g. Dworzynski et al., 2012). The reported gender ratio in ASD varies according to the age and type of population studied. Large-scale studies of

This essay details past and current research into the area of human birth seasonality. It focuses on the contrast in the mechanisms affecting the energetic regulation of ovulation (ERO), which leads to birth seasonality between tropical and temperate subpopulations. In doing so, the seasonal nutritional conditions of females in sub-Saharan Africa and Nepal are evaluated, as well as the climatic and cultural factors that affect the hormonal balance that creates ERO. The essay finds that whereas decreased energy intake causes ERO and therefore birth seasonality in tropical agricultural/pastoral populations, it is increased energy expenditure that has the same effect in temperate agricultural/pastoral populations. Finally, current directions in the field of ERO are briefly explored as they relate to birth outcomes that remain unlinked to seasonality in industrialist populations.