Over the past 150,000 years humans have manifestly been migratory, travelling into vastly different climatic regions of the globe. Darwinian evolution can lead to genetic differences in populations living in different climates, but any mechanism that can protect individuals from relatively short-term changes in living conditions that differ from those in which previous generations lived will also be highly advantageous. If a mother can transmit to her unborn offspring cues that will affect its stature, metabolism and a host of life-history characteristics, she will be at an advantage in fitness terms over a mother who cannot. Paradoxically the reasons for thinking that this has indeed been the case is best found when things go wrong. (more…)