One of the all-time best books I've read on men, women, and how we got that way.
Deft, literate, informed, but laugh-out-loud funny, by a writer who uses words the way Van Gogh used paint.

Doubtless thanks to its original "Sperm Are From Men . . ." title, prudes and Bible-thumpers prevented this book from being a best-seller in its first incarnation. But it's the all-time easiest way to teach any teenager about the birds, the bees, and that hot number who sits down front in Math class and won't ever smile back. Just leave this book visible around the house. It'll promptly disappear for a week or so. You'll have lots less explaining to do.

But first, read it yourself! You'll learn why there are several millions different genders (according to which switches get tripped in the developing fetus); why being gay is genetic, why bowerbirds go to all that trouble, why men and women have evolved different mating strategies, why gorillas are so poorly endowed, and other arcana you'll never forget.

As a side benefit, Quirk is one of the true masters at coining aphorisms.
His book is a enriched-uranium mine for anyone who has to utter sentences in public!