Boy dolphins often try to impress girl dolphins by giving them a sponge as a gift.  Male Australian humpback dolphins present large marine sponges to their favorite females- sometimes getting so excited that they aggressively throw the sponges at their desired mate. They also work in pairs with other males, making them one of the only species besides humans that use ‘wingmen.’  ()

The more biological older brothers a man has, the stronger his chances are of being gay.  It’s called the fraternal birth order effect, and it has to do with the mother’s immune response to certain male antigens while pregnant, which increases with each pregnancy.  (, , )