Biological sex is usually described in simple binary terms: male or female. This works well for germ cells (sperm versus eggs), but for other body organs it is of little help. A new study by the Max ...

The specialized arm that male octopuses use for mating is also a sensory organ that can detect the ovarian hormone progesterone, according to new experiments conducted by Pablo Villar and colleagues.

Male and female reproductive systems allow human reproduction. Fertilisation occurs when a sperm and egg join to form an embryo. An embryo develops into an unborn baby in the uterus during pregnancy.