Cooperation and conflict in human pregnancy.

For many humans living today, obstetric care begins early in pregnancy, and most babies are born in hospitals. These are precautionary measures. Medical complications during the brief nine months of pregnancy are such a common part of human experience that we rarely ask ourselves why gestation does not always proceed as smoothly and reliably as the lifelong beating of our heart or filtration of blood by our kidneys. The birth of a healthy child is central to reproductive fitness and must have been subject to strong natural selection. Why then should placentas be less reliable organs than hearts or kidneys? Why should maternal hearts and kidneys be more subject to catastrophic failures during pregnancy than at other times? A crucial contrast distinguishes obstetrics from cardiology and nephrology. The coordinated activities of heart and kidneys take place within an individual comprised of genetically largely identical cells, whereas pregnancy involves an interaction between genetically-distinct individuals whose cooperation is obviated by evolutionary conflicts of interest.