the placenta regulates a pregnant mother’s immune system, as it does for most mammals. But it’s especially true in the human body, where our extra-invasive placenta has to work extra hard to hold its ground. Evolving ways to make the maternal immune system look the other way makes perfect sense for the embryo, because in the trench warfare of maternal-fetal competition, you really do want to strip the enemy of its bigger guns as soon as possible.
