Eve: How the Female Body Drove 200 Million Years of Human Evolution

by Cat Bohannon

Put it this way: The average vagina is only three to four inches deep. When a woman is sexually stimulated, hormonal changes tense the ligaments holding the uterus and cervix in place. This makes them rise relative to the vaginal opening as the vagina expands its depth considerably. But a six-inch aroused vagina does not accommodate a seven-inch erect penis. In other words, there’s nothing usefully adaptive in a long human penis when four to six erect inches will do the job. In evolutionary terms, that is probably why the average erect human penis is still only a bit over five inches long.[*24] And yet, in a number of studies, heterosexual women rate pictures of men with longer penises as more attractive. There is, in other words, a disconnect between the human penis as a sexual show trait and its functionality.