In 1994, no eight-year-old girls died in Sweden. Not from poisoning or bone cancer; not from meningitis or car accidents: none. In 1994 there were 112,521 eight-year-old girls, and the following New Year’s Day they had become exactly 112,521 nine-year-old girls.
This, evolutionary biologist Armand Marie Leroi admits, is a statistical fluke. But it represents centuries of medical progress against childhood mortality. Historically, we live in a uniquely safe time. For all our fears of murder, plagues, and plane crashes, the vast majority of us will live long and die of drearily familiar ailments: heart disease, cancer, and so forth. We die from internal failures—from aging, a series of slowly unraveling genetic vulnerabilities. “Were it not for aging’s pervasive effects,” Leroi notes, “95 percent of us would celebrate our centenaries; half of us would better the biblical Patriarchs by centuries and live for more than a thousand years.”
If conquering death is medicine’s ultimate goal, then perhaps the ever shortening genetic sequences called telomeres, where a cell’s regenerative powers trickle away like hourglass sand, are the goalkeepers. But—surprise!—there are cells whose telomeres don’t shorten, and they thrive vibrantly with endless life. Cancer cells.
Oops. Turns out immortality will kill you.
Our life is a paradoxical series of simultaneously death-defying and death-inducing compromises. Nowhere is this clearer than in our own genetic heritage. “The average newly conceived human,” notes Leroi in Mutants: On Genetic Variety and the Human Body, “bears three hundred mutations that impair its health in some fashion.”
Mutants is a fascinating account of both how we are created and how we are inexorably undone. Mutation sounds frightening, and it is frightening: Humans are deformed by a nightmarish array of defects. Yet without mutations, we could not exist, for alterations in the genome have taken us far indeed. “We are, in many ways,” Leroi muses, “merely worms writ large”—albeit big, hairy, talking worms. And we are progressing still, each of us playing our part, with our personal arrays of both new and inherited mutations.
In evolutionary terms, the only mutations that matter are ones that enable or disable reproduction. A set of mutations that turned men into dazzlingly attractive and virile studs who dropped dead at age 45 would, over time, beget a world filled with men dropping dead at 45. Mutations that are fatal or deter mating in youth are the only truly bad mutations. Genes that make you croak of a coronary while you are going to the mailbox for your pension check, while most unfortunate for you personally, are essentially irrelevant. Once you’ve reproduced, Mother Nature is free to toss you aside like an empty beer can. So slow-acting mutations are free to proliferate: Their combined deleterious effects get lumped under the general term of aging. This is why, decades from now, those healthy eight-year-old Swedish girls will get picked off one by one by internal flaws that they were born with.
Some mutations are barely discernible: say, left and right thumbs that don’t quite match. One in 10 adults has an extra pair of ribs, often without knowing it. (Check your X-ray next time you’re in the hospital; if you have 26 ribs, you’re in the club.) But other mutations are terrifyingly powerful: Leroi’s examples include everything from everyday killers like Huntington’s, Alzheimer’s, and Lou Gehrig’s disease to such bizarrely fatal infant mutations as a stillborn baby with a second mouth in his forehead. Leroi also recounts a child with 21 half-developed fetuses lodged in his brain, and individuals like Harry Eastlack, whose fibrodysplasia ossificans progressiva meant that with each bruise or injury, repair tissue formed as bone instead of flesh. His remains resemble a melted skeleton candle, a living stalagmite—or, as Leroi memorably puts it, a “forty-year-old man encased in another skeleton.”
The mutations in Leroi’s text push every imaginable boundary of the human form: There are hermaphrodites, cyclopes, dwarfs, albinos, and Siamese twins. Take the spectacular case of Rita Hoefling, who at age 40 had her skin change from white to black. She had the great misfortune to live in South Africa under apartheid; her white family and friends shunned her, and wouldn’t even take her back a decade later when her old skin color returned.
Pathology, Leroi demonstrates, is essential to medical progress; it is hard to know exactly what a gene does until it goes wrong. And while it is easy to describe these cases as abnormal, normality itself is a moving target. Any mutation that can reproduce has a chance at eventually becoming the norm. What was abnormal may become essential, while what was once normal may become extinct. Mutations kill and disfigure—but they are also how a species survives.
Mutants is not a book for the fainthearted; given the array of deformed baby skeletons on display, I wouldn’t recommend it to expectant parents either. And yet its deformities illuminate our forms. Leroi’s debut is a gloriously inquisitive and even hopeful journey into the making and unmaking of human beings, a recognition that genetic variation is essential to life even as it bears us down to our graves. We are all mutants; to our evolutionary ancestors, we must seem monstrously strange progeny. Or, as one 19th-century French anatomist cryptically scolded: “There are no monsters—and nature is one.”