No one knows why Hypospadias, a birth defect where the urethral opening is abnormally placed, became more common among Swedish boys in recent decades. Before 1990, it happened in 4.5 per 1,000 boys, and after that increased to 8 per 1,000 boys.
Researchers looked at past attributed causes (in epidemiology, they find two curves that go the same direction and attribute causation), such as low-birth weight, being born a twin, or being born from in vitro
fertilization (IVF) to conceive, but the curves did not match.
Maybe it was less reported in 1973. No one can say. So they created a new cause out of thin air: endocrine disruptors.