Kin selection
An alternative hypothesis for lekking is kin selection, which assumes that males within a lek are related to one another. As females rarely mate outside of leks, it is advantageous for males to form leks. Although not all males within a lek mate with a female, the unmated males still receive fitness benefits. Kin selection explains that related males congregate to form leks, as a way to attract females and increase inclusive fitness. In some species, the males at the leks show a high degree of relatedness, but this does not apply as a rule to lek-forming species in general. In a few species such as peacocks and black grouse, leks are composed of brothers and half-brothers. The lower-ranking males gain some fitness benefit by passing their genes on through attracting mates for their brothers, since larger leks attract more females. Peacocks recognize and lek with their brothers, even if they have never met before.