Darwinian medicine is Evolutionary Medicine
When George Williams and I were ready to submit our first paper, he insisted on calling it, "The Dawn of Darwinian Medicine." I objected. Evolutionary medicine seemed less controversial, and did we dare be so grand? He convinced me that evolution was a generic term for change that did not even necessarily imply natural selection, that it was Darwin's ideas that we were applying, and that we really were trying to do something big. He was right. But ever since, I have explained that evolutionary medicine and Darwinian medicine are the same. Both terms describe the enterprise of using the principles of evolutionary biology to solve problems in medicine and public health. And, to use problems in medicine and public health to inspire evolutionary biologists to new thinking and projects. It is emphatically not a method of practice and it is in no way opposed to standard scientific medicine, in fact, its main goal is to ground all of medicine and public health in evolutionary biology as well as proximate biology.
We began our work by arguing for months about why selection shaped breast cancer, gastric ulcers, atherosclerosis, and the appendix. Finally...finally we recognized our error--Selection does not shape diseases so looking for evolutionary explanations for diseases is like a walk in a bog. Selection does, however, shape traits that are surprisingly vulnerable to failure. The appendix and narrow birth canal are obvious, but inability to better regulate cell division and inflammation are responsible for huge amounts of disease. Such traits do have evolutionary explanations. It was this small change in the target of explanation, from diseases to traits that leave us vulnerable to diseases that kick started the field. Not that people had not asked such questions before. But we encouraged people to take them very seriously indeed, always comparing the body as it is, to the body as it could have been. Over and over again, we discovered that we were mistaken in our quick assumptions about how the body could be improved. However, we also found plenty of examples where path dependence or chance historical events left bodies with traits, such as our inside out eyeballs, that no engineer would countenance for a minute! Anyone who thinks evolutionary medicine sees the body as perfect is not paying attention. A deep evolutionary view reveals the bodies of all organisms as bundles of trade-offs, compromises and limitations that ensure that perfection is impossible.
The core advance of our work was a very simple-- recognition that natural selection can explain not only why some many things in bodies work so well, it can also explain why so many aspects of bodies seem to be so vulnerable to failure. Such traits had long been fodder for conversation. We encouraged taking such questions very seriously, posing and testing specific hypotheses. The challenge of understanding why bodies are not better inspired years of work on how best to approach such questions. We finally settled on six categories of reasons why bodies have traits that leave them vulnerable to diseases. Sharp observers will note that the below list is slightly different from the one's George and I created early on.
- Mismatch with environments, whether from modern technological environments, the big changes at the origins of agriculture, or from migration.
- Co-evolution with pathogens that evolve vastly faster than we can. This shapes defenses and counter defenses that tend to be expensive and vulnerable to failure.
- Constraints inherent in the evolutionary process, including drift, path dependence, mutations, the instability of development, and more.
- Trade-offs are involved in every trait. Making one trait better will make another worse.
- Reproductive success... for genes... at the expense of health. It is so disturbing to recognize that traits that increase vulnerability to disease are nonetheless selected for if they increase reproduction.
- Finally, defenses such as pain, fever, and anxiety are often thought to be diseases but they are actually useful defenses shaped by selection in conjunction with mechanisms to express them in situations where the benefits are greater than the costs. The "Smoke detector principle" is an application of signal detection theory that explains why defenses are so often apparently expressed excessively, a principle that should guide every physician every day, except that few understand it yet.
The classic article is a good place to start, but the Scientific American version is short, and the recent chapter I wrote with Richard Dawkins for the Oxford Textbook of Medicine is shorter yet. If you are teaching or taking a class, take a look at the "Ten Questions..." article, my attempt to provide a framework for thinking clearly about how to test hypotheses in evolutionary medicine.
MOST USEFUL ARTICLES/BOOKS
Nesse RM, Williams GC: Why We Get Sick: The New Science of Darwinian Medicine, Times Books, New York, 1995. Also published by Weidenfeld and Nicolson, London as Evolution and Healing: The New Science of Darwinian Medicine. Translations completed or underway to German, Italian, Portuguese, Korean, Japanese, Mandarin, Spanish. Das bild Wissenschaft . Book of the Year-1997.
Nesse, RM On the difficulty of defining disease: A Darwinian perspective. Medicine, Health Care and Philosophy, 4:37-46, 2001. New translations available in French and German. See Kransheitstheorien edited by Thomas Schramme, Suhrkamp, 2012, and Philosophie de la medecine by Elodie Grioux et Mael Lemoine, Librairie Phiolsophique J. VRIN, Sorbonne, 2012.
Nesse, RM: Maladaptation and natural selection. Quarterly Review of Biology 80(1):62-70, 2005. My best statement of the six evolutionary explanations for vulnerability.
Nesse RM, Bergstrom CT, Ellison PT, Flier JS, Gluckman P, Govindaraju DR, Niethammer D, Omenn GS, Perlman RL, Schwartz MD, Thomas MG, Stearns SC, Valle D. Making evolutionary biology a basic science for medicine. PNAS;107(Suppl 1):1800-8007, 2010.
Nesse RM, Dawkins R. Evolution: Medicine’s most basic science. In: Warrell DA, Cox TM, Firth JD, Benz EJJ, editors. Oxford Textbook of Medicine, 5th edition. Oxford: Oxford University Press. p. 12-15, 2010.
Nesse RM, Williams, GC On Darwinian medicine. Life Science Research 3 (1): 1-17, 1999. (In English and Chinese)