Race and Ethnicity

The Morning Teatime of Darwinian Medicine

Darwinian medicine seeks to understand our vulnerability to disease.

Posted February 29, 2012

In 1991, George Williams and Randy Nesse published a now classic paper entitled "The Dawn of Darwinian Medicine." Twenty-one years later, much has been accomplished, as we sit at the morning teatime of Darwinian medicine, with a nod toward lunch, and a wink toward afternoon scones.

Darwinian medicine seeks to understand our vulnerability to disease. Why do we still get sick? The very question is thought-provoking and makes you think about medical issues from a unique perspective. After tens of thousands of generations of evolution, shouldn't humans have evolved defense systems that make sickness a thing of the past—something we only read about in history books, not a cause of modern misery? We clearly haven't. Schopenhauer was right on the mark when he said, "If the immediate and direct purpose of our life is not suffering, then our existence is the most ill-adapted to its purpose in the world."

The power of Darwinian medicine, spearheaded by Nesse and (the late) Williams, is that it distills our vulnerabilities to diseases down to six basic causes:

1. We have been, are, and will forever be in a deadly evolutionary arms race with our pathogens. These pathogens evolve much more rapidly than do humans, and so they have a huge one up on us. There are things we can do today with antibiotics and vaccines that were the stuff of dreams until recently, but, as we see every day in headlines about antibiotic resistance, the pathogens fight back—and this is a fierce arms race, with much at stake.

2. Over the last 30,000 years or so we have radically changed the environment on the planet. Some of our vulnerability to disease is the result of insufficient time for natural selection on humans to "catch up" with health-related problems that are the consequence of this rapid environmental change.

3. We have to deal with trade-offs imposed by the laws of physics and biology. For example, if we just had thicker bones we could reduce the number of fractures that we suffer, but, alas, that would come at the expense of nimbleness and speed, which are also quite beneficial.

4. Natural selection is completely devoid of foresight. What that means is that sometimes we are stuck with historically contingent relics of our evolutionary past. Take choking for instance. According to the National Safety Council, this is the fourth leading cause of accidental death. But why do we choke at all? At one level the answer is simple: choking is the result of the intersection of the trachea with the esophagus—the route that air takes through the nasal cavity to the trachea and into the lungs intersects the route that food or water takes through the mouth to the esophagus and into the stomach. Sometimes the pipes get crossed, and we choke.

Fine. But this is a really stupid system. Any first year engineering student could design a system in humans in which the trachea and esophagus don't intersect. Why hasn't natural selection produced such a solution in humans? Yes, the epiglottis has evolved as a partial work-around to this problem, but it is still a far cry from good design. We are stuck with the choking problem because of our evolutionary history. Lungs arose very early in primitive fish, as a pouch of esophagus or gut tissue that probably served to trap gas bubbles and capture additional oxygen in low-oxygen environments—there was no choking risk, because lungs merely provided a backup to the gills. Over evolutionary time, gills were lost in land creatures, and lungs became the source of oxygen. Herein lay the problem. Because lungs and the developmental process by which they are generated arose as an extension of the esophagus and its development, rather than as a separate organ system, this breathing apparatus could not easily be decoupled from the feeding apparatus from which it arose. Hence sometimes we choke. So it goes.

5. Natural selection favors traits that increase reproductive success, not health and well-being. This nasty fact is often overlooked in the medical community. Yes, many times traits have positive effects on reproductive success and health, but that is not always the case, and, from an evolutionary perspective, when there is a conflict, reproductive success always trumps health and well-being. For example, the physical decline associated with old age or the risk-taking behavior associated with adolescence may be adaptive if the alleles responsible also contribute to reproductive success.

6. Some of our suffering results from fever, nausea, and anxiety. These defensive reactions may be unpleasant to experience, and we may lump them into the "symptoms" of being ill, but they are often beneficial adaptations in and of themselves rather than maladies.

If we want to combat illness and disease, we need a deep understanding of why we remain vulnerable to them in the first place. Darwinian medicine provides the framework to do just that.