Knowledge of humanity passes through masculinity and femininity. In other words, we can't understand ourselves individually as men or women if we don't have each other. When the author of Genesis says that "the Lord God then built up into a woman the rib that he had taken from the man," and "brought her to the man," he revealed God's critical intention--man was to have a partner like himself in dignity but also different from him in every way--especially on a physical level. And the author tells us that the man himself recognized this as a good exclaiming "at last, this is bone of my bone and flesh of my flesh!"