ISEMPH Presentation Featured Speaker: Stephen Stearns
“What is a patient?”
Stephen C. Stearns
Professor of Ecology and Evolutionary Biology
Because they evovled, patients are not machines designed by engineers with replaceable parts. They are bundles of tradeoffs because adaptive advances in one trait are often bought at a cost in another. Patients contain ancient constraints that include asymmetric cell division, a precondition for the evo- lution of aging; the use of stem cells for tissue repair, which predisposes to cancer; invasive placentas,which predispose to metastasis; and bipedal locomotion, which complicates birth. Patients vary individually for both genetic and environmental reasons. They vary genetically in ability to resist disease and metabolize drugs. They vary phenotypically in many respects. Early-life experi- ence is particularly important: thin infants are at increased risk of cardiovascular disease, obesity, and diabetes in late life; infants born by C-section are at increased risk of asthma, allergies, and obesity; and children who have more antibiotic treatments are at greater risk of obesity and allergies. Patients age because evolution has shaped them to trade reproductive performance for decreased maintenance; this creates vulnerabilities to degenerative disease. Because aging has many proximal causes that differ among individuals, every person ages in a unique way: if we fix one problem, another will emerge. Patients are unusual among primates in important ways. We have short inter-birth intervals; we are large and fat at birth; that extra fat helps our brains to continue to grow for another 7 years. But our interbirth-intervals trade off with the survival rates of our offspring; our physical vigor trades off with disease resistance in males; and reproduction trades off with maternal survival. Patients consist of about 10 trillion mammal cells, 90 trillion cells of bacteria and fungi, and a much larger number of viruses. Our microbiota has co-evolved with us, colonizes every tissue exposed to the environment, and provides us with essential benefits, including protection from infections, the ability to digest certain foods and synthesize essential nutrients, and signals that initiate the proper development and function of our immune system. When we disrupt our microbiota, a mismatch results that produces some of the diseases of civilization. Patients are indeed an open physico-chemical system, but they are also very importantly an evolved system with organic nuances that go well beyond physics and chemistry. Those evolved nuances that have many significant medical consequences. Professor Stearns specializes in life history evolution, which links the fields of ecology and evolutionary biology, and in evolutionary medicine. He moved to Yale in 2000 from the University of Basel, Switzerland, where he had been professor of zoology since 1983 and held several administrative posts. His books include Evolution, an introduction (Oxford, 2000, 2nd Ed 2005) with Rolf Hoekstra, Watching, from the Edge of Extinction (Yale, 1999) with his wife Beverly Peterson Stearns, The Evolution of Life Histories (Oxford, 1992), and two edited volumes, Evolution in health and disease (Oxford, 1998, 2nd Ed 2008) and The Evolution of Sex and its Consequences. (Birkhäuser, 1987). Prof. Stearns co-founded and has served as president of both the European Society for Evolutionary Biology and the Tropical Biology Association and was founding editor of the Journal of Evolutionary Biology (JEB) and Evolution, Medicine, and Public Health (EMPH), where he currently serves as Editor-in-Chief. He has been a vice president of the Society for the Study of Evolution and is a fellow of the American Association for the Advancement of Science, an Honorary Member of the Swiss Zoological Society, and a Distinguished Fellow of the European Society for Evolutionary Biology.