Evolutionary medicine is an emerging field, and one of my principle research interests. Evolutionary medicine helps explain many ailments and diseases. For example, the fever response, which is an immunoresponse and not caused directly by any pathogen. Another example comes from primatologist Robert Sapolski, who wrote a wonderful book about how stress damages every system in the body and why, called Why Zebras Don’t Get Ulcers. Our current understanding of why our preferred diets (high fat, salt and sugar) tends to cause diseases like diabetes is pure evolutionary psychology: we evolved tastes for things which were both rare and incredibly valuable to survival in a by-gone era. When I have before written that evolutionary psychology is both successful and expansive, these are part of the evidence. You probably know of some of these without having thought of them as evolutionary psychology.
A familiar and high-profile example is antibiotic resistance. The misuse of antibiotics can directly lead to the evolution of nastier, resistant bugs. I was fortunate enough to have lunch the other day with a specialist in this area, who had come to UCLA to brief the doctors here. Here are a few interesting bits that came up in our discussion.
The flu shot might actually be bad for you, in the long haul. Infections from the actual pathogen induce superior “lateral” resistance versus the vaccine. What this means is that infection from the flu better primes your immune system to fight off mutant, similar forms in the future versus than if you had got the flu shot and never contracted the actual flu. There are other considerations, of course. Without vaccinations, many more people will get the flu in any given season which induces an economic and medical cost. Groups that are at serious risk of death from the flu, such as infants and the elderly, should always get vaccinated. Nonetheless, it is good to know these things.
Medical researchers are innovating new ways to use antibiotics which use evolutionary mechanisms to our advantage, instead of disadvantage. One such method is the use of antagonistic pairs or groups of antibiotics. It is possible to have two related antibiotics, let’s call them A and B. If you use A, most of the bugs die, but the few remaining which are resistance to A survive and reproduce and eventually dominate. However, such resistance some in the form of a modification of particular receptors on the bacteria such that more resistance to A means less resistance to B. The harmful bacteria is thus selectively bred for vulnerability and B can then annihilate it.
In cancer treatment, the mindset that a tumor must be destroyed asap might not be the best strategy in all cases. This is true because cancer is actually evolution in progress within your own body. What you use to treat a tumor influences the evolution of that tumor, perhaps leading to resistance to chemotherapy as a result of using it. An alternate strategy was testing in mice: use chemo only when the tumor is growing and not otherwise. In the study, some of the mice who recieved traditional treatment were dead, but 100% of the mice which recieved the alternate tumor management treatment were alive at the end of the study.
The skepticism part
What I have heard, is that doctors tend to rely too heavily on established precepts and are reluctant to reconsider them. One example given above pertains to cancer. Another is the advice we’ve all heard that we should always continue a line of prescribed antibiotics until they are gone. The logic of this advice is simple, make sure the antibiotics have time to kill every single germ they can to prevent a resurgence. But from the evolutionary medicine perspective, this can be self-defeating: you’ve just incubated resistant versions which you may have no ability to fight off later. Had you used no antibiotics (here I’m assuming we’re talking about non-lethal illness, such as an ear infection) your body would subsequently have a strong resistance to that germ and many similar mutants in the wild. You would not have incubated a super-bug.
This is a very controversial and ethically complex point: it isn’t just that we should not over-prescribe antibiotics, it’s that often we should not prescribe them at all, even if they work. The purpose in taking antibiotics is very often to end a painful or uncomfortable illness more quickly, not to save your life. Most infections are not life threatening. But in doing this, we’ve traded comfort for long term risk. Sometimes, short term risk. The antibiotics your doctor gives you today could directly lead to the evolution of bugs which kill you a year or ten years from now. This is not something that most doctors are thinking about, and generally, that they want to think about.
