The Mother's Womb Tests the Viability of the Fetus

Given the invasive nature of pregnancy, it’s perhaps not surprising that the primate womb has evolved to be wary of committing to it. Mammals whose placentae don’t breach the walls of the womb can simply abort or reabsorb unwanted foetuses at any stage of pregnancy. For primates, any such manoeuvre runs the risk of haemorrhage, as the placenta rips away from the mother’s enlarged and paralysed arterial system. And that, in a sentence, is why miscarriages are so dangerous. It’s also w...

 Ontogeny Recapitulates Phylogeny

The similarity between different vertebrate embryos is indeed remarkable. Since the early 1800s, embryologists have been struck by the parallel between early development in various animal species and their evolutionary relationship, a resemblance conveniently abbreviated by the saying "ontogeny recapitulates phylogeny." Of course, each of us does not really pass through a "lizard" stage on our way to a fully developed human form. But it is true that animals who are more closely related in ter...