First science post in a long time. Expect more though. Because I feel like I’m in a political rut.

I get more than a little frustrated when doctors and fellow medical students tell me they don’t see how evolution has any bearing on the practice of medicine. Perhaps it’s because they’re taught to think of the body as a machine that on occasion malfunctions and needs to be repaired, and so find themselves inclined to think of Paley’s watch rather than Haeckel’s famous theory. Perhaps it’s because they view biology as a means to an end rather than the end in and of itself. Whatever the reason, Dobzhansky’s most famous utterance is lost upon far too many of them.

Learning
A knowledge of evolution makes understanding several subjects considerably easier. This applies to embryology perhaps more than any other. As a tutor for the dental students at my university, I’ve found phylogenetic comparison an invaluable teaching aid. I’ve also found it immensely frustrating since, being in Oklahoma, I have to preface it with “I don’t know if you’re a creationist or not, but this is an evolutionary example that helps me understand things.” When helping students to understand why the sclerotome of the paraxial mesoderm forms only axial skeletal elements but not appendicular (limb) bones, I invoke the humble lamprey. Possessed of the simplest body plan, the poor creature lacks both limbs and a true jaw. I tell them “The sclerotome is pretty old stuff, it’s only got enough material to produce a lamprey skeleton.” Vertebrae, ribs, and a skull encasing the brain and eyes. That’s about it. Jaws, ‘faces’, and limbs, being newer vertebrate features, have a different embryological derivation. And a lightbulb goes off. “Paraxial=lamprey”. Stupid simple.

Staying with embryology just a few moments longer, the development of the kidney is a rather confusing process. The embryo/fetus actually develops three different excretory systems in succession, the latter two of which are functional at various points of development. First come the cervical nephrotomes, then the mesonephros, then the metanephros. This developmental process is an elegant (and possibly the finest) example of the idea that ontogeny recapitulates phylogeny. And because of this, a sprinkling of evolutionary context can help to make sense of this process well enough for a student to keep things straight.

Perhaps the most fun use of evolutionary perspective comes when learning about physiology. Everything in physiology revolves around homeostasis. Maintaining a constant internal environment. For the most part, complexity of a given taxon is directly proportional to its ability to maintain its internal state at a constant rate. Mammals are perhaps the finest example of this ability, but all, from the simplest ball of Volvox to the lizard basking in the sun show some aptitude for this. And as to the nature of this internal state they’re trying to maintain? Blood bears a remarkable (or perhaps expected) resemblance to seawater in many respects. And this has prompted several of my physiology teachers to describe us as “a collection of cells that figured out how to take the sea with us.” Much like Wernstrom’s goldfish and his reverse scuba suit.

The greatest vindication of the use of evolutionary history as a teaching aid is the fact that although these represent extra–what mainstream physicans would less charitably call extraneous–information, they nevertheless make the testable material easier to understand. In short, the extra learning investment is more than returned.

Looking Forward
Evolutionary thinking also gives us a more stable platform from which to study the human body in sickness and in health. Understanding that the human body is an evolved construct allows us to better understand exactly what ‘normal’ is, and what conditions may bring on disease.

Anatomically and genetically, humans haven’t changed all that much in the past 100,000 years. Yet our environs and our lifestyles have shifted to the point that our current circumstances have no resemblance whatsoever to our past lives. More importantly, as technology, healthcare, and standards of living have improved, we are less and less likely to die before reproducing no matter how feeble or infirm.

What this means is that we have to treat the body as evolutionarily static at least from the birth of modern H. sapiens, and perhaps even as far back as H. heidelbergensis. And although I am somewhat critical of the view of the body as a machine, it remains a useful framework within certain limits. The heating element in your water heater would quickly warp if powered up in open air. And the coil on your stovetop wouldn’t function under water. Their failure under such circumstances is not an indicator that they are defective, but rather that they were forced to operate outside their design parameters.

I hate to use the word ‘design’ in such a context, but preventive medicine hinges upon our ability to ensure that our bodies are not placed in situations they haven’t evolved to cope with. Diet, activity patterns, and exercise are just a few of the areas in which we differ from earlier examples of our species. How does this deviation affect our health? In the realm of genetics, sickle cell anemia is probably one of the most well-known examples of the intersection of evolution and medicine. A potentially beneficial allele in one environmental context becomes nothing but a nuisance at best, lethal at worst in another. Type II diabetes is another example.

My personal agenda revolves around the basic proposition that the brain’s purpose isn’t whatever some psychologist claims it is, but rather that it is wired and coded with software that is designed for a certain environment. It is not a blank slate but an evolved construct optimally suited to certain physical and social contexts. When placed in a different social or learning structure, it can easily go haywire.

The latest area of medicine I’ve seen a place for evolution in is cancer. This might be because we just finished the unit on neoplasia in pathology class and I’d been studying it 24/7 for the past couple weeks. But everything about the pathogenesis of cancer hearkens back to lessons I had in undergrad on selective advantage, differential reproduction, and natural selection. Without getting into too much detail, cancer is essentially a progression of genetic changes, each of which allow these cells to escape the restraints that prevent normal cells from proliferating and spreading unchecked. The neoplastic cells that beget a tumor were often present 10 or 20 years before anything was clinically evident. This is because the immune system ruthlessly destroy those cells that appear genetically different from the host. Like multi-drug resistant bacteria, those neoplastic cells exist in an environment that consistently selects for the ones that evade detection, escape destruction, and reproduce faster than they can be killed. The ability of these tumors to continually reappear despite the immune system’s best efforts, and in many cases from apparently successful chemotherapy should thus come as little surprise when thought of this way. We are in fact selecting for those mutant genes that confer the ability to escape normal therapeutic and preventive methods.

We, our genes, our physiology, and our behavioral patterns evolved in one environment. They are a product of that intimate interaction between the organism and its surroundings. Changing the surroundings not only changes the nature of the interaction, but may substantially affect the fitness of said organism. While nothing so dramatic as the explosion of a polychaete worm when placed in a freshwater aquarium, there can be little doubt that much of the ’cause’ of human illness may not be rooted internally at all. Understanding the difference between our current environment and the one we evolved in will play an ever greater role in the prevention and treatment of disease.

Conclusion
Medicine has much to learn from evolution. It can provide us a foundation from which to better ground ourselves. And a scaffolding from which to reach for the sky. No other facet of the biological disciplines has remained as recalcitrant to simple Darwinian concepts as this field, and perhaps it’s time we were brought kicking and screaming into a mindset most of our colleagues found in the early 1900’s.