Genetic conflict may play a role in pregnancy complications, such as preeclampsia and gestational diabetes, as well as developmental disorders.

Bits of viral genes incorporated into human DNA have been linked to cancer, ALS and schizophrenia. But many of these genes may not be harmful, and could even protect against infectious disease.

A fetus needs oxygen long before its lungs work and it's exposed to the air. Some ingenious biochemistry explains how the mother's blood delivers it.