Evolution of invasive placentation with special reference to non-human primates.

It is now possible to view human placentation in an evolutionary context because advances in molecular phylogenetics provide a reliable scenario for the evolution of mammals. Perhaps the most striking finding is the uniqueness of human placenta. The lower primates have non-invasive placentae and even tarsiers and New World monkeys show restricted trophoblast invasion. Moreover, a truly villous placenta occurs only in Old World monkeys and great apes. The two latter groups of haplorhine primates show varying degrees of trophoblast-uterine interaction, including differences in the extent of decidualization, formation and disintegration of a cytotrophoblastic shell, degree of interstitial trophoblast invasion and depth of trophoblast invasion into spiral arteries. Recently, the occurrence of human-like deep invasion was confirmed in gorillas and chimpanzees. As the still enigmatic disease of pre-eclampsia also occurs in these species, such information may reveal the evolutionary roots of this disease of impaired maternal-fetal interaction.