Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
The Female of the Species (poem) "Female of the Species". The title was again lifted in 2006 for Joanna Murray-Smith's satirical play "The Female of the Species". A 1946 novel by James Hadley Chase was titled "More Deadly Than The Male". Another novel, written by Mindy McGinnis, is titled “The Female of the Species.” In 1984, Off Centaur Publications released an audio tape cassette album titled "The Horse-Tamer's Daughter" featuring a song based on the poem, set to music by Leslie Fish and performed by Julia Ecklar. In 1998, the song was nominated for a Pegasus Award for "Best Adaptation" by a ballot of science fiction