The end of conflict: the placenta and imprinting

The placenta is the unique organ of therian mammals, key to their evolution and viability. The chorion is the outermost of the extra-embryonic membranes, and in birds and reptiles it is a simple membrane in contact with the shell allowing gas exchange. But in eutherian mammals the chorion is highly vascularised by the allantois to form the placenta. While the placenta serves the common role in all eutherian mammals of supporting fetal nutrition and oxygenation, serving as the route to excretion and providing an immune barrier between the mother and fetus, there are enormous species differences in the structure of the placenta. (more…)

Weather forecasting or maternal manipulation?

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…)