Fetal-maternal conflict, trophoblast invasion, preeclampsia, and the red queen.

The much publicized conflict hypothesis for understanding fetal-maternal interaction during pregnancy often invokes a 'battle' metaphor, rather than a well orchestrated interplay occurring as a series of well controlled moves and counter-moves as happens in a game of chess. Such stepwise interaction is particularly obvious in the spiral artery remodelling process, and it would be interesting to trace the history of the successive steps in histological adaptation throughout primate phylogeny. The restricted invasion observed in a few species on a 'lower' evolutionary scale suggests a tendency of progressive deeper invasion during primate evolution. Unfortunately, our knowledge of invasive processes in the placental bed in nonhuman primates is highly inadequate. A paradigm underscoring the stepwise interaction between mother and fetus may be provided by the Red Queen hypothesis, which is a useful model to explain co-evolutionary processes between different species. The apparent association between preeclampsia and restricted endovascular trophoblast invasion, combined with the absence of the disease in primate species showing shallow invasion, suggests that preeclampsia may result from a failure in one or more interactive steps necessary for deeper invasion. Evidence for a genetic component invokes the puzzling question as to why "preeclampsia genes" are not eliminated from human populations. As in other fields of medicine, a proper understanding of Darwinian selection processes may throw some light on the causes of preeclampsia.