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Seasons of Life – Russell G Foster and Leon Kreitzman

Almost universal weight loss is a common feature of the pre-harvest season among the Lese women in the Ituri Forest of the Democratic Republic of the Congo.  This weight loss is accompanied by lower levels of salivary progesterone and oestradiol, longer inter-menstrual intervals, and shorter durations of menstrual bleeding.  All these trends are reversed after the harvest, as a positive energy balance is established.  Over time this seasonal variation in ovarian function is reflected in a statistically significant seasonal pattern of conceptions after the harvest……….

During our history, the pressures on an agrarian economy that was largely dependent on the seasonal weather, meant that social organisation, and with it conception and birth timing, was closely tied to the requirement to provide the necessary labour force for the peak times of planting and harvesting.