When I was a child, it was believed that animals became extinct because they were too specialized. My father used to tell us about the saber-tooth tiger’s teeth — how they got too big and the tiger couldn’t eat because he couldn’t take game anymore. And I remember my father saying, with my brother sitting there, ‘I wonder what it will be with the human beings that will be so overspecialized that they’ll kill themselves off?’

My father never found out that my brother was working on the bomb.

— Richard Feynman’s sister Joan, quoted in Christopher Sykes, No Ordinary Genius, 1994