placenta

A light micrograph of a human placenta showing blood that will enter (red) or has exited (blue) the fetus

LENNART NILSSON, TT/SCIENCE PHOT

THE human placenta is riddled with cancer-like patterns of mutations. But the discovery is better news than it might appear: it is helping scientists open a new window on the mysterious world of early human development.

In some ways, the placenta is a forgotten organ. It begins to form shortly after fertilisation from the embryo’s cells and then helps to support the future fetus as it develops before it is discarded at birth.

But it …