Sexual desire may be a powerful impetus for bonding in animals but is an enormous barrier to comfortable relations among human beings. The reason is that sexual desire is rarely exactly reciprocal between two persons: as a rule, either the man lusts more passionately after the woman than she does for him, or vice versa. But in the end, no one wants to lust after an unwilling, or even less willing, partner; nor does anyone want to be lusted after, and be the 'sex object' of a more lusting partner. This may be the main reason why sexual attraction and desire cannot serve as the foundation for marriage or a lasting friendship.
Thomas Szasz, 'The Untamed Tongue: a Dissenting Dictionary'
Great photo, thanks for sharing!