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When it comes to boobs, male scientists have traditionally reverted to their tongue-wagging, Sears-catalog-pawing adolescence. For decades, male academics peddled the problematic theory that breasts evolved because guys liked to grope them. Then a new generation of women scientists poked holes in that theory, as author Florence Williams delectably unveils in her enlightening book, Breasts: A Natural and Unnatural History. Turns out human breasts—which are unique among primates—probably evolved the way they did so they could be maximally efficient nutrient-delivery mechanisms. Pendulous pom-poms, sexualized though they may be, are also quite good at drooping to meet the mouths of tiny babies. That’s just one of the titillating (sorry!) facts found in Williams’ book, a frequently witty and consistently informative history of the wonders of mommybags. But Breasts isn’t always a light read: Chapters on chemically tainted breast milk (most American mothers have it) and breast cancer (we’re all at risk) might scare the daylights out of women who’d never given much thought to either. Breasts, it seems, sponge up carcinogens like diapers in a kiddie pool. It’s surprising Williams is able to fill a book with tales of breasts, but unlike our life-giving chesticles, they never seem to get old.

Florence Williams discusses and signs her book at 5 p.m. at Politics & Prose, 5015 Connecticut Ave. NW. Free. politics-prose.com. (202) 364-1919.