Mary Roach's 2003 book, Stiff: The Curious Lives of Human Cadavers, was my favorite book that year. Science writer Roach dove into studies done on dead bodies in morbid detail—like how budding plastic surgeons practice facelifts on severed heads. Roach is as funny as she is fact-oriented, often sprinkling in oddball anecdotes as footnotes, which made learning about cadaver organ harvesting actually entertaining.

Her newest book, Bonk: The Curious Coupling of Science and Sex, has the same conceit—explore the science of sex with a humorous bent. Unfortunately, the concept didn't translate as well with this arguably more sensitive subject.

Part of the problem with Bonk is Roach's source material. Not surprisingly, clinical studies of sexual physiology and behavior are just that—clinical. I found myself wishing for diagrams, so I could fully understand what the "pelvic floor" and "dorsal vein" look like, and how they play into things like orgasms, fertility, and impotence.

Roach, however, seems surprised that scientists like William Masters and Virginia Johnson, who published 1966's Human Sexual Response, didn't note irrelevant details such as what was playing on the stereo as they studied human copulation. Still other attempts at exhaustive reporting run into obstacles like shy subjects or wary review boards. And when Roach attempts to overcome that problem by becoming the subject in a few studies, she stunts the book by super-sanitizing her account so she "wouldn't mortify" her two stepkids.

Moreover, Roach's subject matter is too broad. In her intro, she explains that there's an assumption that "people study sex because they are perverts," which has a chilling effect on sexual research. That alone is enough for an entire book, digging into the personalities of scientists who buck convention to examine such a basic human function. Instead, Roach wanders all over—from monkey mating rituals and what they tell us about human hormones to whether people can think themselves to orgasm—but reaches few conclusions.

I wasn't expecting a titillating book. But with source materials and research limited by the "cringe factor," as she describes it, Bonk is far less polished and interesting than Roach's prior works.