 His mother was Lady Nora Barlow, daughter of Sir Horace Darwin.He was a great-grandson of the naturalist Charles Darwin.Although Erasmus has been a common name in the family since the time of his great-great-great-grandfather Erasmus Darwin, he was named after his mother's brother, his uncle Erasmus Darwin IV who was killed at the Second Battle of Ypres on 24 April, nine days after he was born.