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Evolution and medicine

Bringing evolutionary thinking to medical research.

I often marvel at the remarkable power of evolution by natural selection to create diverse, intricate, and exquisitely well-adapted forms of life. Just this morning, for example, I read a paper about how spiders use the Earth's electric field to loft into the air and balloon for a hundred miles or more on tiny threads. It's wonderful and glorious to contemplate what evolution has managed to do in shaping life on this planet — but it also makes it all the more galling that my own body performs so poorly, from chronic lower back pain to the colds and flus that go around every winter, from the commonplace anxiety to the ubiquitous myopia of professional academics. If evolution is so smart, why am I such a mess?

The field of evolution and medicine aims to answer this question. Our approach is not to posit adaptive stories for disease, but rather to seek evolutionary explanations for our vulnerability to disease. This involves two lines of attack. One is to recognize that our nemeses — pathogens and parasites — are themselves evolving rapidly, and to study the processes by which they evolve with an eye toward improving prevention and treatment. The other is to recognize that our own bodies are the products of an evolutionary process, and use that awareness to understand sources of ill health. Both approaches suggest new hypotheses and explanations which can shape the medical research agenda, and ultimately influence medical practice.

“If evolution is so smart, why am I such a mess?”

The relevance of evolutionary biology is readily apparent. Containing the spread of antibiotic-resistance bacteria in hospitals, preventing avian flu from triggering a human pandemic, or even slowing the progression of HIV within an individual patient — each of these problems is literally an exercise in applied evolutionary biology. Meanwhile, oncology is undergoing a revolution based on the recognition that the growth of a tumor is itself an evolutionary process.

In order to anticipate and to contain disease spread and disease evolution, we need to understand the underlying population biology and population genetics of both pathogen and host. Conversely, through the wealth of available data and the rapidity of the pathogen evolution, infectious disease biology offers to population biologists an opportunity to observe evolution taking place in "real time," and as such provides a rich set of study systems for biologists who are interested in the basic ecological and evolutionary principles. In the past I have worked on the threat posed by antibiotic resistant bacteria and on the processes by which zoonotic pathogens such as H5N1 Avian Influenza (bird flu), SARS coronavirus, and Ebola virus emerge into human populations.

I see a fruitful opportunity to integrate medicine and evolutionary biology when thinking about the evolution of immune systems and about how pathogens evolve to evade immune defenses. A core question is "how do immune systems avoid subversion by pathogens that rapidly evolve to hide from host defense or defuse host attacks?"

I am also interested in understanding our vulnerability to the debilitating mood disorders that affect more than a quarter of all Americans at some point in their lives. To get the root of this puzzle, I think we need to understand the evolutionary function of mood in the first place, and move from there to explore why mood systems can become dysregulated. In short, it seems that mood provides a way of modulating our motivation states in response to changing environments. To then explain mood disorders, we need to be able to explain how an evolved system with this function could become dysregulated and why natural selection has not corrected the problem.

My course BIOL 469: Evolution and Medicine provides a venue for me to share my interest in this area with bright and enthusiastic college seniors on an annual basis.