Charles Darwin's paternal grandfather, Erasmus Darwin, made the Darwin name famous well before Charles was born. Erasmus was accomplished in many different fields. One of England's leading medical authorities, he was asked to be the personal doctor of King George III. He was a prolific inventor whose achievements included a horizontal windmill to power the Wedgwood factory. He was also a popular poet and natural philosopher whose ideas were credited with inspiring Mary Shelley's novel Frankenstein.

Erasmus's radical views included opposition to slavery, support for women's education, sympathy for the French and American revolutions and a theory of evolution that predated Charles Darwin's by several decades.

Erasmus's son Robert—Charles's father—was also a physician. But unlike his outspoken father, Robert was sober and respectable. Charles accordingly grew up in a dignified, upstanding household.