Us cruel humans. We produce babies whose kneecaps aren’t bone yet but expect them to crawl. Their cartilage kneecaps take at least three years to harden; other bones begin 11 weeks before birth, when softer tissue ossifies. The process continues into adolescence. When your teenager oversleeps, give him a break: He’s still making bones. There is much that startles in “Skeleton Keys,” Brian Switek’s cultural history of bone, not least that bone is startling at all. We mostly see it when it’s dead: a skeleton, a skull. We think of bones as white, brittle and inert, not rich and dynamic. Yet bone is mobile in more ways than one. It makes possible all kinds of locomotion, to “stomp, fly, swim, slither, dig, run.” Inside the body, new bone cells are constantly forming while osteoclast cells slough off others, a process known as resorbing but that Switek more memorably embeds in my imagination as “something like what happened to the deck of Nostromo in ‘Alien’ when the face hugger’s acid blood melted through the floor.”Switek, a science journalist who has written about dinosaurs, wants to use his book to unlock the past, present and future of our inner scaffolding, our 206 bones — a figure repeated too often — that make our extraordinary skeleton. The dinosaurs are here only to cast their big crowd-pleasing shadow over the rightful stars: the fossils and fish that offer clues to how we became who we are, an upright bipedal mobile mammal with swiveling elbows. The next time I hear music, I’ll thank the “twitchy fish” that began to form jaws and then ears. Peter Benchley, who gave us fiction’s most memorable man-eating shark, probably should too. Without them, as Switek points out, his novel might have been called “Pharyngeal Slit” or simply “Hole.”CreditFrank Franklin II/Associated PressSwitek is an affable guide, and affability is required when the depth and breadth of his subject is so vast, when many characters are fossils or skeletons and most field trips are to yet another museum. His tone can veer from chatty — he writes of collagen that “splorts” — to overly academic, and there is enough repetition that one could wish for a sharper editorial scalpel. At one point Switek hesitates to call a female skeleton from a tar pit “La Brea Woman” because of current theories on sex and gender, eschewing “biological sex” as presumptuous and sticking to “osteological sex” instead. I’m none the wiser at the end of this sticky muddle. (And later in the book, Switek happily uses “biological sex” again.)We are on surer ground with his skeletal actors, displayed to us, and displaying in turn episodes of illness, deformity, history and ethics. Read of poor Harry Eastlack, whose body turned soft tissue to bone, or of the deformed skulls of the children of Toulouse, and I defy you not to wince. He revisits the gripping detective story surrounding bones under a parking lot that turned out to belong to King Richard III. Its lead actors are the DNA and chemical isotopes in the bones, the slashes and slices that showed his awful prolonged death in battle. There are thoughtful explorations on the right way to treat the dead, when they have often been treated so wrongly. One shameful episode was the accidental digging up of human remains in Iowa in 1971 by construction workers: While 26 European settlers who were unearthed were sensitively sent for reburial, the bones of a Native American mother and child were handed over to the state archaeologist.I sit here now crossing my extraordinary kneecaps and thinking of my dissolving bones. I wish my favorite fact about bone had not been missing — that the marrow inside these things, judged inert and ignored, makes blood, the most vivid biological substance — but there is plenty to compensate. My skeleton may be invisible, and I’d like it to stay that way. But now, when it comes to these “endless forms most beautiful and wonderful,” to borrow Darwin’s words, I can see them better thanks to Switek’s keys.Rose George is the author of “Nine Pints: A Journey Through the Money, Medicine, and Mysteries of Blood.”SKELETON KEYS The Secret Life of Bone By Brian Switek Illustrated. 276 pp. Riverhead Books. $26.A version of this article appears in print on , on Page 9 of the Sunday Book Review with the headline: Dem Bones