Nothing in medicine makes sense except in the light of evolution! So goes a modification of the great 20th century evolutionary biologist Theodosius Dobzhansky's statement about biology; Dobzhansky was advocating the teaching of evolution in the schools, but his quip is now tailored as the dictum of the field of evolutionary medicine (EM).
EM is the idea that evolutionary theory can be used to explain why we get the diseases we do. That is, when something goes wrong with the body, it's because our genome evolved long ago, in a very different ecological context, and thus we're not adapted to life in the modern world. We're out of sync with our evolutionary history, and this is what leads to disease. And should, as a consequence, inform clinical practice.
A very nicely argued paper by Michael Cournoyea in the latest Perspectives in Biology and Medicine ("Ancestral Assumptions and the Clinical Uncertainty of Evolutionary Medicine") questions the theoretical basis of this idea, as well as its clinical relevance. He refers to two recent collections of writings on EM, noting that they include chapters on
...nutrition, type 2 diabetes, childbirth, menstruation, stress, altitude sickness, sleep, heart disease, obesity, addiction, delusions, and more. For example, contributors suggest that addiction is just the malfunctioning of ancestral wanting and seeking mechanisms in modern lifestyles; sleep problems reflect an ancestral tension between the need to remain vigilant and the need to rest; and the life of those with chronic heart failure may be prolonged by blocking ancient neurohormonal adaptations.These kinds of arguments are not uncommon even in everyday analyses of modern society: it's often said, e.g., that severe anxiety disorder is common in today's stressful society, when we have to do things we did not evolve to do like public speaking or driving across bridges. But anxiety evolved as a normal defensive response to fearful situations, and at the time was adaptive rather than debilitating. Too little anxiety would have been selected against, because, well, it's obvious -- he who had no fear of lions was dinner.
Cournoyea describes the classic example of the practical uses of EM. Fever, it is thought, must have evolved for a reason. Because it accompanies illness, it must somehow help the immune system combat infection. Therefore, it's probably best to leave fever untreated. But, as he says, while this idea might pinpoint a way for researchers to study fever, it isn't clear that this is relevant to clinical practice, and the conclusion warranted.
Cournoyea stresses the difference between evolutionary explanations on the micro scale (antibiotic resistance, or the evolution of influenza viruses, e.g.) and the macro scale ("the origin and adaptive function of physiological processes" such as breast-feeding), noting that the application of evolutionary theory to the first is much more informative than the speculative kinds of applications that are considered in the longer time scale, and indeed the only kinds of applications that can be considered since these traits evolved so long ago. Why did fever or menopause evolve? These questions can't be answered other than speculatively. Yet, much of evolutionary medicine is dedicated to answering such questions. And, as Cournoyea points out, generally from a strong adaptationist perspective.
I conclude that faults in these fundamental assumptions undermine EM’s central objective of providing clinically relevant medical knowledge. I maintain that evolution’s place in the clinic is controversial at best, and that these conceptual blind spots lead to misguided conclusions about our supposed human nature.As he also points out, many evolutionary theorists by now have questioned the assumption that all traits have been molded by natural selection to be highly adaptive, but EM is built on this assumption. "Developmental constraints and the nonselective mechanisms of evolution are given a backseat to adaptive functionality..." But, he writes, explanations of ultimate causation, the adaptive hypotheses put forward by EM, are not relevant to clinical practice. And we think it is defensible to assert that many who make evolutionary arguments of this sort have only a cartoon understanding of how evolution works.
And there's more
As regular readers of MT know, we harp on the problem of assuming adaptation and the all-encompassing role of natural selection in evolution, all the time, so we are in complete agreement with Cournoyea's critique of EM in this regard. But there's another fundamental problem with EM that Cournoyea's spot-on paper doesn't address -- not that it should -- and that is the idea that we evolved in a given environment to be highly adapted to that environment, and that one alone.
Organisms that are highly adapted to a single environment, unable to adapt to change, are very vulnerable. Or, put another way, extinct. One of the most ubiquitous characteristics of life, so ubiquitous that we've called it a principle of life, is facultativeness, the ability to adapt to change. The "paleo diet" craze is another 'philosophy' founded on the idea that we evolved to eat the raw foods that our ancestors ate as they were becoming modern, and thus that we only achieve optimal health following that diet.
But by this logic, we're in danger of going down Alfred Russel Wallace's slippery path to excepting humans from evolution. And he was by no means alone in invoking human exceptionalism in such contexts (Darwin did it in his own way, too). Indeed, we might even find ourselves attending seances as Wallace did late in life. He thought that the human ability to do calculus was evidence that it was impossible for us to have evolved by natural selection alone, because the human brain didn't evolve doing calculus. Similarly, because we didn't evolve eating Twinkies, they must be lethal.
But we can do calculus, because what evolved was our brain's ability to figure things out. We didn't evolve knowing how to cross busy city streets either, but we can do that, too, and we can build rockets and go to the moon. And, people eat a huge range of foods now, and have done as we evolved -- there are 7 billion of us on Earth, speaking thousands of languages and still eating varied diets, so clearly we're adaptable. There's no one way to be human -- nor are there single pathways to disease.
Fairy stories can't always be refuted, but that doesn't make them true
Just because we can invoke -- or, basically, assume -- a principle of nature, like natural selection, this doesn't mean that the principle works without exception or is invoked in an empirically correct way. But if a tale is being told that rests on that assumption, there is a very widespread tendency to let the assumption slip by without justification, and accept the fable and its moral. Fairy stories can't be refuted if the existence of fairies is assumed, not something to prove before we judge the story itself.
Likewise, despite Darwin's venerable insights, natural selection is a possible aspect of evolution -- nobody can doubt that -- but it is an aspect, not a law of nature. Other factors, notably chance and implications of organizational complexity, greatly modify what one can legitimately say about selection. This is so widely understood by those who care to look at things carefully that there is no excuse for the widespread uncritical selectionism so widely assumed about Nature by so many, in evolutionary medicine but also in evolutionary psychology, too much of anthropology, genetics, and beyond.
If you assume that some trait is the result of natural selection, then you can make up stories as to how it worked to produce your particular trait. If your first guess doesn't fit, then you feel justified to make up counter-adaptationist stories. But if selection is assumed, it can't be refuted since it's not open to test.
Just because a tale is possible, or seems plausible, this does not in any way make it true, especially if its basic premise is not open to question, as is so often the case in biomedical research or EM.
And Dobzhansky's quip?
The co-opting of Dobzhanksy's quip is very telling. As we also noted in our book MT, even in its original form with respect to biology, it is manifestly untrue. Did nothing in biological research make sense before Darwin? While nothing in biology (or medicine, for that matter) is inconsistent with our understanding of evolution, it is just not true that nothing 'makes sense' except in that context.
The blatantly obvious truth of this is that much of biomedical research has nothing to do with evolution, as well as the fact that many if not most people in the field know very little about evolution beyond a caricature (and, of course, many creationists of various religions work in biology and medicine). But the slogan can be routinely invoked without any critical assessment by almost anybody, even in biology, including a cult -- and that's the right way to characterize it -- of a few leaders of EM whose words seem rarely to be questioned, much less critiqued properly. This fact shows that invoking the quote isn't that different from saying a rosary: a comfortable, feel-good reinforcement of what often amounts to little more than a mantra of an ideology. That's not the same as science!
It's a shame people have to be this way, because the scientific challenges are serious, and there is much that we don't know about evolution; the subject deserves better for its own sake, and for the public that pays for results.