Cue the '70s porn music: Male Mexican Mollies who sport something resembling a mustache are a hit with their female counterparts. Physorg describes the newly discovered mustache as a "series of epidermal outgrowths" on the upper lip of the small freshwater fish. US and German researchers tried to figure out the growth's purpose and concluded it's "a previously unrecognized sexually selected trait." Females prefer mustachioed mates, and one researcher thinks the 'stache is used as a lovemaking tool.
(Read more fish stories.)