THERE'S NOTHING LIKE STARING at mountains to remind us of breasts — their magnificence, their evolutionary brilliance, their voluptuous tug on our collective psyches. In French Un teton (as in Grand Tetons), means the tip of the breast. So it seems fitting that an intrepid science writer living near the Rocky Mountains in Boulder, Colorado was inspired to undertake the time and effort required to produce such an important piece of reportage as Florence Williams has done with Breasts: A Natural and Unnatural History.

Seven years ago, just as she was blissfully nursing her second child, Williams read a series of reports about industrial chemicals winding up in human breast milk. There went her fantasy that breast milk was like "ice cream, Valium and Ecstasy all wrapped up in two pretty packages." On assignment for the New York Times Magazine, Williams had her own breast milk tested and discovered it had levels of flame retardants — from electronics, furnishings and food — ten to 100 times higher than that of women in Europe. She wanted to know if it was still okay to breast feed at all. And, she wondered, will women ever be able to produce relatively uncontaminated milk again?

With a scientist's mind, a journalist's eye, and a mother's heart, Williams has produced a wide-ranging environmental history of the breast, in which she addresses such questions as: why girls are sprouting breast buds earlier (and facing an increased breast cancer risk as a result), how breasts have gotten bigger since the Second World War, and the chicken-and-egg conundrum of which came first in the evolutionary scheme of things — breasts for succor or breasts to attract males. Williams, a visiting scholar and research fellow in environmental journalism at the University of Colorado, has, in her own words, a "dogged sense of granola-girl duty," and as a result she is a thorough and dependable guide to understanding issues big and small about endocrinology, biology and epigenetics.

"We are not simply agents of environmental change, we are also objects of that change," she explains. "Our breasts soak up pollution like a pair of soft sponges." Williams delineates one of the most consequential dramas at the intersection of human evolution and environmental change, that is, "how our breasts went from being honed by the environment to being harmed by it." According to the CDC, breast cancer is now the most common cancer among women.

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While this could obviously be a depressing enterprise, Williams is an accomplished writer with a wicked sense of humor, provocative and insightful. As she points out, the book's publication coincides with the fiftieth anniversary of two seminal events: the publication of Rachel Carson's prophetic environmental primer Silent Spring, along with the first silicone implant surgery in Houston. Carson died of breast cancer in 1964, but Williams tracked down the first silicone implant patient, Timmie Jean Lindsey. In exchange for a cosmetic surgery she didn't want, namely new breasts, Lindsey got one she did want — her ears pinned back — by two plastic surgeons working with Dow Corning. She was, in other words, their human guinea pig. Over time, her implants hardened and caused "shooting pain" in her chest. Most silicone implants last for 10 to 20 years, but Timmie Jean still has the original ones 50 years later. (Though her im...