Lack of basic research has hampered assisted reproduction

On the third day after fertilisation a human embryo is made of six to 12 roughly identical cells; on day four its cells appear to fuse into a mostly uniform blob; and on day five it puffs out to reveal two completely new groups of cells—an outer layer that will go on to form the placenta, and an inner clump that will develop into the fetus. How this happens is a mystery. So is how things happen after day six—a particularly frustrating one, given that it overlaps with the crucial stage during which the embryo readies itself for implantation into the wall of the uterus and a pregnancy either begins or does not.