Guest post written by: Eirik Garnas
Most medical doctors know very little about evolution, which is not surprising, given that the vast majority of medical students don’t learn much about evolutionary biology, Darwin’s theories, or ancestral health. The same can be said for practitioners and students who are involved in other health-related fields, such as nutrition. I should know, as I’ve studied both nutrition and sports science. During those years at school, I only heard the word evolution mentioned a couple of times, and never in the context of the etiology, pathogenesis, or prevention of human disease. I find this lack of focus on evolutionary concepts extremely concerning.
“Nothing” in nutrition or medicine makes sense except in the light of evolution. If doctors and nutritionists have no evolutionary framework to guide their understanding of health and disease, they are incapable of doing their jobs properly.
I strongly believe that an infusion of evolutionary science into health-related fields such as nutrition and medicine could revolutionize our entire medical system. To someone who is not knowledgeable about evolutionary biology or Darwinian medicine, this notion may seem far-fetched; however, to someone who’s dug into the scientific literature on the aforementioned topics, it probably doesn’t.
Humans, like all other organisms on this planet, are a product of evolution. There is a reason why our bodies work the way they do; a reason why we do better on some diets than others; and a reason why we get sick. To find these reasons, we need to look back and examine the evolutionary processes that got us to where we are today.
Evolutionary science helps us answer questions that otherwise can’t be answered
There’s an evolutionary explanation for “everything”. Sometimes, this explanation presents itself quickly and clearly, whereas other times, we have to dig long and hard before we find the answers we’re looking for. In the end, though, the explanation can usually be found via the evolutionary route. It may not be fully formed and explain everything we need to know, but it gives us a foundation upon which we can build our ideas and understanding.
I know this may seem abstract to a lot of people, so, in order to make things more graspable, I thought I’d illustrate the point with a few examples. Below are some medical-related questions that can be answered using evolutionary theory:
- Why does antibiotic resistance develop?
- What types of diets are humans best adapted to eat?
- Why does our body temperature typically rise when we get an infection?
- Why are humans so susceptible to develop back and knee pain?
- How and why do some gut organisms “hijack” our brain?
- Why are many diseases and health problems more prevalent today than they were in the Paleolithic?
- What type of microbiota is the human body adapted to harbor?
- Why do we think and act the way we do?
- Why isn’t the human body “perfectly” designed?
- Why and how do cancer cells evolve and spread?
Medical students learn a lot about the molecular mechanisms underlying disease; however, they learn little about evolutionary biology and ancestral health; hence, they are incapable of fully answering the questions above – which can only be properly answered using evolutionary logic.
The science of Darwinian medicine: 10 things we’ve learned over the past decades
In this article, I’m not going to take an in-depth look at the science of Darwinian medicine. That would require hundreds, if not thousands of pages. Rather, I thought I’d summarize some of the things we’ve learned over the past decades. Some of these things have been known for quite some time, at least within certain scientific circles; however, it’s only recently that they’ve received solid scientific support.
- Many human diseases and health problems, including acne vulgaris, type-1 diabetes, heart disease, obesity, and the metabolic syndrome, are caused, in large part, by evolutionary mismatches (i.e., a mismatch between the human genome, which is comprised of genes selected in the past, and the modern milieu, which differs markedly from past environments) (1, 2, 3, 4, 5).
- Cancer evolves via natural selection (6). In order to understand how cancer cells develop and spread, we must first understand the game of evolution.
- Humans’ microbial environment has changed dramatically over the past 10.000 years (7, 8). These changes have likely contributed to driving the increased incidence and prevalence of many chronic diseases, in particular those that are associated with chronic inflammation (7, 8).
- Modern, imprudent diets change the gut environment in such a way that a microbiota that is incompatible with human genetics develops (9, 10, 11). These changes occur as a result of selective processes in the gut; when the environment changes, the microbiota also changes; those microbes that are best adapted to survive and reproduce under the new conditions proliferate, whereas those that are poorly adapted wither or die.
- Paleolithic, hunter-gatherer style diets are useful in the treatment of many health problems and markedly improve body composition and markers of cardiovascular and metabolic health, among other things (12, 13, 14, 15).
- Contemporary humans who move into the wild for a period of time and adopt a hunter-gatherer style lifestyle experience rapid health improvements.
- Genome-microbiome mismatches, caused by recent changes in humans’ environment, may underlie a long list of diseases and health problems.
- Humans’ physical activity requirements were determined in the past. Many human diseases and health conditions, in particular those associated with the bones, cardiovascular system, and/or muskuloskeletal system, such as osteoporosis and heart disease, are partly caused by the replacement of a physically active hunter-gatherer lifestyle with a sedentary, modern lifestyle (16, 17).
- Humans’ propensity to develop certain health problems such as back pain may partly be explained by the occurrence of trade-off situations earlier in human evolution. (E.g., when our ancestors started to walk upright, they became better at some things, such as looking over tall grasses, but worse at other things, such as climbing. They may also have become more prone to develop certain muskuloskeletal problems).
- Humans didn’t evolve as single entities; we evolved alongside a cloud of microbes. A growing body of evidence shows that a progressive loss of biodiversity (biome depletion) from the human superorganism, starting about 10.000 years ago, with the transition from hunting and gathering to agriculture, may be at the root of a long list of health problems (7, 8, 18). Biome reconstitution, guided by evolutionary thinking, is a key measure required to slow down and reverse the increasing incidence of immune-related health problems in the developed world (7, 8, 18, 19).
I could go on; I haven’t even gotten into infectious diseases, which can also be “explained” by evolutionary theories. However, in order to keep this article from getting too long, I think we’ll stop there.
My impression is that the vast majority of scientists agree that evolutionary theory contributes to our understanding of health and disease. However, some make the case that it doesn’t help us much in terms of the prevention and treatment of disease. I disagree. After having read the list above, I think you probably do as well. As clearly shown in the summary, evolutionary science doesn’t just help us understand why we get sick, but it also informs us about what we should do to prevent and reverse disease.
That said, it’s important to remember that natural selection doesn’t select for health; it selects for reproductive success. It only “cares” about health if there is a link between the health of the organism and its ability to survive and reproduce. Usually, though, there is a link between the two. Even more so in the past than now, it was a tight connection between the physical fitness and evolutionary fitness of each member of our species.
Evolutionary science doesn’t necessarily provide us with clear-cut answers as to what we should do to combat disease; however, it does equip us with a conceptual framework that helps guide our understanding of health and medicine.
A gaping hole that needs to be filled
If the things I learned in school were all I knew about nutrition and health, I wouldn’t be very knowledgeable, and I certainly wouldn’t be able to give you a good answer to the questions posed earlier. In school, I learned a lot about chemistry, anatomy, physiology, and the molecular basis of disease, but I learned nothing about evolution, ancestral health, or Darwin’s theories.
If I was put in charge of designing the curricula of study programs in Nutrition and Medicine, I would definitely make some changes from their current state. Most importantly, I would add at least one mandatory course about evolutionary biology and ancestral health. Preferably, the students would have this course early on in their education, so that they are equipped with an evolutionary framework that they can use to understand and make sense of other subjects they learn about later in their educational journey.
I don’t claim to have all the answers, but if there’s one thing I know, it’s that modern medicine and nutrition are in desperate need of an infusion of evolutionary theory. Evolution via natural selection is the guiding principle in biology. Medicine and nutrition could be considered sub-disciplines of biology; hence, it goes without saying that Darwin’s theories are important also here.
Here’s what a 2016 research paper entitled Evolutionary Science as a Method to Facilitate Higher Level Thinking and Reasoning in Medical Training had to say about the importance of incorporating evolutionary science into medical education:
“Clearly, the ramifications of natural selection for medical practice and research are wide-ranging. To be prepared to practice medicine in the 21st century, medical students need to master the concept of natural selection, as well as other evolutionary concepts fundamental to medicine.
…we would argue that the relevance of many of evolutionary medicine’s tenets such as “evolutionary mismatch” is actually increasing. This is due to increasing globalization and the export of the Western lifestyle around the world, and the rate at which Western societies are accelerating away from the conditions under which our species evolved. These forms of environmental change will bring about new health challenges that will be best addressed with an evolutionary perspective.” (20)
Is change coming?
These days, new studies and papers about Paleolithic diets, the old friends theory, biome reconstitution, and other topics related to Darwinian medicine are published all the time. Unfortunately, though, this science has not made its way into universities and colleges. These institutions are slow to change; sometimes, it can seem like they reject change – even when new evidence is standing on their doorstep, knocking to get in.
Hopefully, as more and more research is published and the knocking gets louder and louder, they will open their doors. The question is: How long will it take before this happens?
I certainly hope it happens in the very near future, but I’m not convinced that it will. It takes time for paradigm changes to occur, in large part because the “establishment” – who’ve been practicing and teaching according to the same set of principles for decades – may be resistant to change how they do things. Their current understanding of health and medicine is so ingrained into their minds that they may dismiss “everything” that doesn’t fit into their established models.
That said, I think a change is bound to happen sooner or later. In nutrition, a field I’m very familiar with, signs of change are already clearly visible, in large part because a lot of Randomized Controlled Trials (RCTs) on Paleolithic nutrition has been published lately. To some people, in particular those who don’t know much about evolutionary biology and don’t understand what the whole ancestral health thing is all about, “hard science” is all that matters: Nothing less than a pile of RCTs and comprehensive meta-analyses will change their mind.
They don’t understand and are not convinced by explanations about gene-environment discordance, trade-offs, or other evolutionary theories; they need to see statistical results and p-values derived from randomized clinical trials before they even consider changing their opinions. Even then, they may be resistant to change how they think, typically because they don’t want to believe that they have been wrong or that another, perhaps seemingly more uncomfortable, path is better than the one they are currently on.
I’m looking forward to seeing how we approach health, nutrition, and medicine in the future. Hopefully, the approach we use in the future will be better – and more evolutionary sound – than the one we use today. A new paradigm may be developed by combining the best from both conventional and Darwinian/evolutionary medicine.
I couldn’t agree more with the researchers of the paper mentioned earlier, which had the following to say in their concluding paragraph:
“We argue that the future of medical research and practice will increasingly require an evolutionary perspective to address the new health concerns of the 21st century. These will include chronic disease, mental health, as well as other issues such as emerging pathogens. The ability of physicians and biomedical researchers to link ultimate evolutionary explanations for disease to their proximate mechanisms shall become increasingly important. Therefore the sooner we revise medical preparation to integrate evolutionary perspectives, the better primed we will be to address the medical challenges of the 21st century.” (20)
Eirik Garnas is a nutritionist, magazine writer, blogger, and personal trainer. He’s written for several different health & fitness websites and magazines, including Paleo Magazine. He is also the founder and owner of www.Darwinian-Medicine.com, a website dedicated to ancestral health, nutrition, and evolutionary medicine. Over the years he’s helped clients of all different ages, body types, and fitness levels build a healthier, stronger body.