# Which species do mules belong to?

**URL:** <https://boards.straightdope.com/t/which-species-do-mules-belong-to/284561>\
**Category:** Factual Questions\
**Created:** [January 13, 2005, 4:12pm UTC](https://boards.straightdope.com/t/which-species-do-mules-belong-to/284561 "2005-01-13T16:12:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![EmeraldGrue](https://avatars.discourse-cdn.com/v4/letter/e/dc4da7/32.png) [@EmeraldGrue](https://boards.straightdope.com/u/EmeraldGrue)\
**Post date:** [January 13, 2005, 4:12pm UTC](https://boards.straightdope.com/t/which-species-do-mules-belong-to/284561/1 "2005-01-13T16:12:35Z")

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We’re told that a horse and an ass belong to different species because their offspring (a mule) is sterile. But what is the mule - a horse, an ass, neither, or both? Or is there a better definition of species that accounts for such cases?

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**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\
**Post date:** [January 13, 2005, 4:23pm UTC](https://boards.straightdope.com/t/which-species-do-mules-belong-to/284561/2 "2005-01-13T16:23:10Z")

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The question seems to assums that all plants, animals, etc., must belong to a species. I would have though that sterile hybrids do not belong to a species.

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**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\
**Post date:** [January 13, 2005, 5:09pm UTC](https://boards.straightdope.com/t/which-species-do-mules-belong-to/284561/3 "2005-01-13T17:09:28Z")

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That is correct. Mules, or other interspecific hybirds (whether sterile or fertile) are not considered to belong to any species. They would be described scientifically as _Equus caballus x E. asinus._