Asimov wrote the story, his twenty-third, in August 1940 under the title "Twins". It was rejected by John W. Campbell, editor of Astounding Science Fiction, on 29 August, and accepted by Frederik Pohl on 4 September. It appeared in the April 1941 issue of Astonishing Stories under the title "Heredity" and was reprinted in the 1972 collection The Early Asimov.