First , the genitals . You ' ve got innies , outties , and . wait , what else is there ? Is this some kind of perverted trick you ' re playing ? Next , you know , the sexual aspects of some third gender . Perhaps they don ' t need other people ? That ' s clearly one option , but you could also allow for sex with male and females . The third sex individuals might mate with both , or , wait a second , why wouldn ' t they only mate with male or female ? There ' s nothing excluding that from the range of possibilities . Of course there are preferences for each sex , like , generally , pink for girls and blue for boys . They individuals might not prefer either color , but one is distinctly different from another . So is that color green ? We ' re starting to form a picture here . Some new form of genitals , sex with either male or female or both , and some new reference of identity . Green , for example , being very indicative of that specific gender . What have we learned in our musings ? Aliens , of course .