Cover by Jack Coggins
Katherine MacLean was born on January 22, 1925. Her novella, “The Missing Man” received the Nebula Award in 1971, and in 2003 she was named an Author Emerita by the Science Fiction and Fantasy Writers of America. MacLean was the guest of honor at the first WisCon in 1977, and in 2011 she was named the recipient of the Cordwainer Smith Rediscovery Award. Best known for her short fiction, which has been collected in three volumes, she has also written three novels and has co-written works with Carl West, Tom Condit, and Charles V. De Vet.
“The Snowball Effect” was first published in Galaxy Science Fiction in the September 1952 issue, edited by Horace L. Gold. It has been reprinted several times, including in MacLean’s collections The Diploids and Science Fiction Collection.