Last week I gave a talk on evolutionary medicine to a group of ~50 medical students at my school. I really enjoy public speaking and I love talking about evolutionary medicine, so I had a blast (and the talk seemed to be well received). I won’t try and recount exactly what I said in my talk, but as people seem to be interested in what I had to say I’ll try and provide a general idea of how the talk flowed, sharing the things that I think medical students should keep in the back of their mind as they go through their medical training.
I started with an introduction to evolutionary medicine…
An image from a 2010 Nature article on Evolutionary Medicine. (Particularly fun as Darwin did start to train as a physician at one point!)
The term “Evolutionary Medicine” is rather broad, and can mean anything from how and why our enzymes work a specific way to why we respond to our modern environment (or a medicine, stress, or toxin) the way we do. It stresses (to me at least) the fact that natural selection is everywhere, and we would do well to remember this (in medicine, business, policy, and life!). The term “Evolutionary Medicine” is sometimes used interchangeably with “Darwinian Medicine”, and is often mentioned during the discussion of “Ancestral Health”. These are all terms I hope that we will hear more of as medical education continues to evolve (selection pressure is everywhere, right?)
Speaking of med schools- I just read that the first lecture new med students get at UCSD is a lecture on evolutionary medicine [1]. Very cool! I like the idea of introducing the subject to med students before the onset of clinical training, as it offers a paradigm in which to think about health and disease, instead of trying to learn everything from a purely mechanistic perspective.
As med students, we are already familiar with some selective pressures that alter human health. Microbial resistance to antibiotics, sickle cell anemia, and lactose intolerance (though perhaps more accurately, “lactase persistence”) are all things we learn about, and are probably (hopefully?) taught with an emphasis on the selection pressures that brought these things to prevalence. These three examples, however, are just the tip of the iceberg.
We can use evolutionary medicine (and indeed I think we should) at all levels of human health and disease, but I think that an excellent starting point for this discussion is to take a step back and look at the bigger picture of “what it is to be human”.
So what is “being human”?
I find the easiest way to look at this question is to ask “how does a human live ‘in the wild’”. I’m not talking about a weekend camping trip, or even a half-year adventure through the rugged arctic, but rather, what can we glean from archeological evidence, our closest hominid relatives, and native peoples about how humans evolved? Alas, many native cultures are converting (or already have converted) to a more modern lifestyle, but there is a lot that we can learn from the lifestyle of people such as the Australian Aboriginals, the New Zealand Maori, Native Americans, Kitavans, Inuit, Maasai, and others. Even though much cultural identity has been lost in recent generations, memories and documentation exist that we can use to better understand traditionally living humans.
I should say, at the outset, that this is not a plea to return to a traditional lifestyle (nor do I think people living in traditional cultures should be barred the opportunity to adopt aspects of our modern life). This isn’t about “going back” or recreating a specific lifestyle. Instead, this is about understanding our past so we can thrive in the present (and beyond).
Perhaps first and foremost (and indeed, my starting point into evolutionary wellness (there I go using yet another term)) is the food that humans thrive on. It is increasingly evident that there is not one “perfect human diet” that we evolved to thrive on. Rather, there are a number of foods that nourish and sustain our body in a healthy way. Humans evolved eating (and indeed some of these things truly ‘made us human’) meat, seafood, eggs, vegetables, fruits, nuts, and tubers.
What about grains and dairy? This is inevitably the cry we will hear from patients, friends, family, and hospital nutritionists! To hear these people talk is to think that humans cannot exist without these two staves of life. As much as people think of these things as staples of the human diet, the reality is that they were most likely not consumed in any real quantity until the agricultural revolution, a mere 10,000 years ago (not much time when you consider the span of human evolution). While it is true some people do well on these foods (and indeed, lactase persistence gave some a significant reproductive advantage at some point in the last 10,000 years), many people do not. Even those that seem to tolerate these things well are often surprised by the benefits they experience when these things are eliminated from the diet. Not everyone does poorly on these foods, but it definitely seems that many have not evolved to thrive on them.
Perhaps more important than thinking about what humans evolved to eat is thinking about what is truly novel in our modern diet. Unnatural trans-fats (not all trans-fats, as there are natural ones such as conjugated linoleic acid (CLA), which appears to have significant health benefits) have been shown to be particularly evil, and a campaign has been waged (mostly successfully) to rid them from our modern diet. With unnatural trans-fats mostly out of the way, the worst of our modern novelties (in my opinion) is the excessive amount of linoleic acid (found in vegetable oils such as corn oil and soybean oil) in our modern diet. I could write a book about the evils of linoleic acid (who knows, maybe one day I will), but without going into detail, excess linoleic acid is associated with increased gut permeability, increased inflammation, and increased fatty liver, just to name a few conditions off the top of my head. I think the westernized world would be a much healthier place if we would eliminate all the modern sources of linoleic acid and again embrace sources of omega-3 fats such as fatty fish and grass-fed meats (but that is enough information for another talk entirely!).
{Ed. Note- I can find it difficult to keep myself on task as I talk about evolutionary health. Since it really gives you a paradigm in which to think, it is so easy to branch off at any place to explore other venues that benefit from an evolutionary approach.}
When considering the declining health of the western world, other culprits in our modern diet are likely excessive sugars, additives and preservatives, soy, hyper-palitable processes foods, a host of other things I can’t think to list right now and, though it is debatable for some as mentioned above, grains and dairy.
Going beyond food- what else makes us human?
A topic that I have been meaning to write on for ages, but that “That Paleo Guy” Jamie Scott has recently been writing quite a bit about, is Sun.
Humans evolved outside, under the sun. Our lives, both daily and seasonally, were controlled by the rising and setting of the sun. Most of us know that UV radiation from the sun is responsible for starting the conversion of precursor compounds into active vitamin D, but how many of us actually get enough sun to be replete in vitamin D, and how much do we actually need? Looking at this from the evolutionary standpoint, we can determine that appropriate vitamin D levels are extremely important for human health and survival. Indeed- it is believed that the drive for adequate vitamin D levels is what drove lighter skin pigmentation in humans as they migrated away from the equator (lighter skin meant that people could still make adequate vitamin D despite the decreased UVB exposure at northern latitudes and the decreased skin exposure due to increased clothes in colder climates).
Vitamin D is also a great opportunity to tap into Ancestral Health as a way to guide modern medicine. For lack of a better description, we in the western world are shooting blind when trying to figure out what is an appropriate target for blood levels of vitamin D. We currently base our studies off of epidemiological studies of humans living well-outside their evolutionary niche and laboratory studies using isolated cells and models quite distant from a living, breathing, human. While these studies can provide us with interesting information (and quite a bit of garbage), can it really give us a good idea of what is optimal for human health? Might information from people living in a traditional lifestyle give us a better idea of how humans have evolved to thrive? A paper recently came out that looked at vitamin D levels in groups of Maasai and Hadzabe and found that the mean Vitamin D concentrations in these population is 115nmol/L (~46ug/L) [2]. Whether this level is “ideal” is uncertain, but it’s an interesting (and arguably more reasonable) place to get started than trying to tease out a reasonable target from the varying levels of insufficiency in most modern civilizations.
The benefits of sunlight aren’t limited to vitamin D. The sun plays other roles in human health, and I will make a strong (personal) argument that sun exposure does wonders for psychological wellbeing!
Humans were meant to move
This is, perhaps, something that everyone can agree upon. This, like food and sun, is something that can be looked at from many different angles under the lens of evolution. How has our body evolved as we became bipeds, and where are the weaknesses in our constitution? Bipedalism changed the shape of our hips, and with it the risks of childbirth. Our shoulders are wonderfully mobile joints, but with mobility comes potential weakness (hello rotator cuff injuries!). And what about feet? Through feats (heh- couldn’t help myself!) of natural selection, our feet have been crafted over millennia to support and move us unassisted, yet now we want to rely on highly engineered shoes to cushion, balance, and protect our feet. Interesting research our of Harvard by Daniel Lieberman’s lab shows some of the effects shoes have on the forces exerted on our knees (cliff notes versions- shoes aren’t doing us any favors). Furthermore, recently the floodgates have opened letting loose a stream of research showing the “dangers of sitting”. These are all elements of human health that can be more easily understood when placed in the context of an evolutionary paradigm.
Humans sleep
This seems like such an obvious statement, but it’s probably one of the hardest things for people to implement. As budding health professionals, we are rarely able to set a good example in this aspect, yet we should realize that cutting short on sleep is detrimental to more than just our coffee budgets. As I mentioned above, until recently, our lives were controlled by the rising and setting of the sun- now we are able to extend our hours (not just of waking, but also working), probably at great expense to our health. Here, as in other aspects of evolutionary health, I’m not recommending that we shun our modern world, but instead that we should understand our modern situation in the light of our evolutionary past and our biology. An interesting evo-health aspect to consider here is the effect of blue light on melatonin production (melatonin is a hormone important in controlling our circadian rhythm). Exposure to blue light decreases the production of melatonin in the brain, thereby affecting our sleep-wake cycle. While we’re unlikely to convince many (indeed you won’t convince me!) to turn my computer off after sunset, we should consider reasonable “hacks” to work around it. For this example, the cool free program f.lux is available, which alters the amount of blue light emitted from your display based on the time of day and your local sunset and sunrise time. If you don’t have it already, check it out!
Humans have friends, not “friends”
I’m not going to waste much time on this one, but real, legitimate human interactions are an important part of being human. I’m not saying you can’t make great friends on the internet- one of my best friends is an internet friend- but a real social bonds take more time and effort than a 140 character message or the occasional “poke”. Meaningful relationships take time, which is something many are painfully short of these days. Alas, the same modern life stresses that make strong social bonds hard to forge and maintain also make such support even more necessary.
Evolutionary Medicine isn’t just about preventative health.
I won’t go into it here, but in the closing minutes of my talk I went on to talk about some of the evo-med examples I have written about here before. First I discussed the likely role of the appendix (and why we should care) and then I talked about an alternative perspective on the etiology of diverticulitis. I also stressed that this talk wasn’t meant to be an all inclusive “this is evolutionary medicine” talk, but more of an opportunity to introduce a subject that I hope my peers will start to consider as they continue their medical education and eventually head off to their specialty of choice.
I’ve only referenced a couple papers in this post, but I did put up a number of papers throughout my talk to show that this is science. There is a growing body of evidence to support the importance of evolutionary thinking in modern medicine, and an increasing interest in teaching evolutionary principles to medical students. As for me- I continue to find great excitement and joy (two wonderful human pleasures) in thinking about these evolutionary principles and how we can utilize them in practice.
1. Varki, A., Nothing in medicine makes sense, except in the light of evolution. J Mol Med (Berl), 2012. 90(5): p. 481-94.
2. Luxwolda, M.F., R.S. Kuipers, I.P. Kema, D.A. Janneke Dijck-Brouwer, and F.A. Muskiet, Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr, 2012: p. 1-5.
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