As most humans find out, the initial stage of romance is one of passion, characterized by physical and emotional attraction and mediated by our senses. Often short-lived, this phase must progress to affection, companionship and mutual respect if the relationship is to last. Indeed, many (if not most) romantic encounters end here.
But, from nature's point of view, that first stage is sufficient. She is concerned with procreation, not with long term relationships. While human societies have evolved to favor such relationships, fortified by the social constructs of marriage and family and closely tied to our belief systems, one might argue that they are unnatural. As we know, many do not endure.
Most of us would likely agree that the family unit enhances the stability of human society; genetic ties are especially strong. Just don't look to nature for her support.
See also: The Genetic Bond and Marriage: an Unnatural Union
