Defining heterosexuality

It's a little harder than you might think:

“We don’t know much about heterosexuality. No one knows whether heterosexuality is the result of nature or nurture, caused by inaccessible subconscious developments, or just what happens when impressionable young people come under the influence of older heterosexuals.” Far more scientific firepower, in other words, has been directed at the brains, genes, hormones and general physiologic processes behind homosexual attraction, leaving heterosexuality like a silhouette, outlined only by what it is not.

Yet the great behavioral descriptionists, Alfred Kinsey and others, have made it clear that sometimes it is exactly what it is not — or, rather, it is what many feel it should not be. From same-sex adults sharing a bed (for warmth? from friendship?) in the 19th century to married men “on the down low” in the 21st, self-defined heterosexuals have routinely behaved in ways that seem to contradict the basic principles.