The vagina is part of the birth canal. A baby's head comes through it during childbirth. Wo there is no way that a penis of any size can impact on the vagina, even if the vagina was an organ with sensitivity to touch, which it is not. The vagina is inert and, unlike the penis, is solely a reproductive organ. Sexual response evolved in both sexes because of the anatomy men and women have in common, the phallus. Given orgasm is a vital characteristic of male reproductive function, it is illogical to suggest that sexual responsiveness could have evolved in women in anatomy that is not present in the male.