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,
Male/Female (Borofsky) as the centerpiece of a re-designed plaza in front of Penn Station. The project celebrated the Municipal Art Society's centennial and was completed in 2004. The sculpture was given to the City as a gift. "Male/Female" has generated considerable controversy ever since its installation. Its defenders cite the contemporary imagery and artistic expression as complementing an urban landscape, while opponents criticize what they decry as a clash with Penn Station's Beaux-Arts architecture, detracting from its classic lines. It has been named both Baltimore's kinkiest piece of public art, "The Invasion of the 50-Foot She-Male" that "bends genders and may very