Some things just can’t be tolerated.

Take, for instance, when food touches other food on your plate. Or when socks don’t match up. Or if, like, somebody, like, repeatedly uses a catch-phrase without, like, thinking.

We all have our individual likes, traits, and dislikes. But are our selves shaped by outside influence, or did we enter the world this way? Was our behavior learned or innate? In the new book “Gay, Straight, and the Reason Why” by Simon LeVay, you’ll find answers to similar questions of a more intimate sort.

Nearly two decades ago, Simon LeVay published a scientific paper asserting that gay men differed from straight men in brain structure; specifically, a cluster of nerve cells controlling sex drive were, in gay men, of the size that LeVay observed in straight women’s brains.

Since the publication of his paper, vast amounts of further research have been done concerning same-sex attraction and the nature / nurture debate. In this book, LeVay takes a deeper look at new findings.

While some gays and lesbians are “surprised” later in life by feelings of same-sex attraction, LeVay says that sexual identity, while not always immediately apparent, is present at birth (although women, throughout life, appear to be more “fluid” and cannot always be categorized). As small proof, he points to several cases in which male infants were, for one reason or another, “assigned” to live as the opposite sex. In most cases, upon adulthood, the “assignment” turned out to be wrong.

Childhood abuse has been theorized to be an influence on gayness, but survivors deny it as a factor. Some theories claim that older siblings hold sway. And as for “choice,” LeVay cites several quasi-claims of “conversions,” in which therapy reportedly changed sexual preference.

Overall, LeVay says, nothing is “cut and dried” but the probable reason that someone is gay has to do with genetics, hormones, and stress that individuals receive in utero. Studies show, for instance, that mice are influenced by chemicals secreted by their mothers and by littermates. Humans, likewise, are affected in similar ways, which could lay to rest so many questions.

And one of the hints may — literally — be at your fingertips.

While there is no doubt that “Gay, Straight, and the Reason Why” is an intriguing book that makes sense on several levels, there’s one big problem with it: you almost need a PhD to follow much of what author Simon LeVay says. Yes, it’s steeped in medical lingo. Yes, LeVay includes a glossary and heavy-duty notes to explain the scientific terms and acronyms. Still, this book is a challenge.

If you’re up for that challenge, though, you’ll be rewarded with a pondering and thought-provoking examination of a private subject that has a very public focus. LeVay leaves no hypothesis unexamined, which leaves readers satisfied that every corner of this argument has been thoroughly dusted off.

Give yourself some time if you decide to tackle this book, because it’s nowhere near light reading. Still, “Gay, Straight, and the Reason Why” is surely food for tolerance. : :

— Terri Schlichenmeyer is “The Bookworm.” Terri has been reading since she was three years old and she never goes anywhere without a book. She lives on a hill in Wisconsin with two dogs and 11,000 books.

“Gay, Straight, and the Reason Why”
by Simon LeVay
c.2010, Oxford University Press
$27.95. 412 pages, includes notes.