Fairy wren nestlings learn “passwords,” or unique single notes, from their mothers while still in their eggs; after birth they must use the passwords when calling for food, or the mothers will abandon the nest. In a 2012 study, scientists in Australia experimented with switching eggs and mothers, and found that passwords were not genetically inherited; the chicks assumed the passwords of their adopted mothers.

The first-century Roman writer Gaius Julius Hyginus relates the story of Agnodice, a young Athenian woman who traveled to Alexandria to study medicine. On her return to Athens she disguised herself as a man in order to practice, and was brought before the court of the Areopagus. “You men are not spouses but enemies,” Agnodice’s patients protested, “since you are condemning the woman who discovered health for us.” Around 500 bc, the law forbidding women to study medicine was repealed.