The Voyage Continues: Darwin and Medicine at 200 Years

ON FEBRUARY 12, 1809, CHARLES DARWIN WAS born in the small market town of Shrewsbury, England. He was an adventurous voyager, as a young man at age 22 embarking upon an epic circumnavigation of the globe aboard the HMS Beagle. However, upon returning to England 5 years later, he attached himself with the tenacity of a barnacle to home and hearth, rarely straying for the remainder of his life. Nevertheless, Darwin’s intellectual voyage had only begun when he took up residence at Down House and over the next 41 years, his sedentary habits would belie a farranging intellect. His insights and clear unassuming prose would bring order to the chaos of biology, expose the mechanisms that underpin life’s diversity, and illuminate the origins of our species. His central idea, the simplicity of which is exceeded only by its stunning profundity, would shake social convention, earning him the sobriquet of “the most dangerous man in England.” It is appropriate now, on the 200th anniversary of his birth, that medicine acknowledges the special debt owed to Darwin; for in the end, explaining the human body in both sickness and in health is an evolutionary endeavor. To paraphrase Dobzhansky, nothing in medicine makes sense except in the light of evolution, an observation that explains the increasing relevance of Darwin’s work to modern medicine and mandates a shift in the training of medical students. The burgeoning recognition of evolutionary biology’s importance to medical science would have delighted Darwin, who as a teenager rounded with his father, an admired Shropshire physician. In fact, Darwin studied medicine in Edinburgh, Scotland, until his squeamishness toward the barbarous nature of that era’s medical practice and his zeal for natural history lead him to flee the medical field. But Darwin recognized that the human body can be understood at a fundamental level only by an exploration of its evolutionary past. Just as the study of political history is necessary to understand how societies have arrived at their present state, evolution illuminates the deep history of the human body that makes sense only in light of that history. Nevertheless, medicine and evolutionary biology seemed to follow separate trajectories for a considerable time after the publication of On the Origin of Species. However over the past decade, physicians have begun to perceive the relevance of Darwin’s work with the growth of an extensive contemporary literature focusing on evolutionary medicine. This new approach to medicine promises cogent explanations for and new approaches to such diverse phenomena as aging, obesity, diabetes, low back pain, and cancer. Evolution’s striking relevance to modern medicine can perhaps best be illustrated by its centrality to the new field of personalized medicine, which seeks to apply sophisticated genetic analysis to tailor health care to the individual. Despite its modern trappings, this new specialty rests firmly on one of Darwin’s most basic (and revolutionary) insights—individual variation. Before the publication of Darwin’s seminal work in 1859, species were considered immutable and fixed. Like the Platonic ideal of the perfect circle, each individual species was considered a reflection of an essential form. Each individual sea urchin, llama, and bark beetle was viewed as an approximation of an ideal; individual variations were seen as irrelevant and inconvenient blemishes, unworthy of study. The fact that humans were evidently different from one another was just more fodder for the idea (also overturned by Darwin) that human beings stand apart from the rest of biology. But instead of ignoring individual variation, Darwin sought it out and realized its crucial import as the raw material on which natural selection acts. Now, 150 years after the publication of On the Origin of Species, medical practitioners are following Darwin’s lead and scrutinizing the subtle genetic variations that make each human unique and when harnessed, hold the promise of revolutionizing health care. Evolutionary theory is as relevant to the teaching of medicine as to medical practice. Just as the periodic table of the elements brings structure to the study of chemistry, an evolutionary approach to medical education provides a logic to understanding the human body in health and disease. Evolution explains why humans are the way they are, ultimately answering the most fundamental questions asked by