Whoever and wherever you are, it’s a good bet that your lifestyle is different from that of your ancestors 500,000, 50,000, 5000, 500, or even 50 years ago. If you’re an evolutionist, that should ring alarm bells. Adaptations take time to evolve. When the environment changes, then adaptations to the ancestral environment may not be adaptive in the current environment. If our lifestyle departs from that of our ancestors, then we potentially live in a world of evolutionary mismatches.

Of course, in many respects our modern lifestyles are themselves adaptations brought about by individual learning and cultural evolution. As one modest example, consider sunscreen. It allows those of us who are genetically mismatched to our solar environment to work and play outside. However, even individual learning and cultural evolution require time to adapt us to our environments, so they are also subject to mismatches on their respective time scales, as anyone who has experienced a major lifestyle change can attest—such as a rich person forced to live on the streets or a poor person attending an elite college on a scholarship.

Sometimes evolutionary mismatches are easy to spot and correct. As a biological example, since time immemorial, baby sea turtles have hatched on sandy beaches and made their way to the sea. The sensory cue that they have evolved to rely upon is reflected light from the sea surface. When houses began to be built along beaches, their lights drew the baby sea turtles landward rather than seaward, a tragic mismatch that can result in the extinction of the turtle population if something isn’t done. That “something” might be a lights out policy during turtle hatching season, brigades of volunteers who collect the turtles and transport them to the sea, or some other intervention that corrects for the mismatch. In this case, waiting for genetic evolution to occur is not an option.

How many of us are like the baby sea turtles, driven to behave in ways that are detrimental to our wellbeing by adaptations to past environments? That’s the question that TVOL will explore in a series of articles that I have organized with the help of two experts. Aaron P. Blaisdell is Professor of Psychology at UCLA, a founding member of the Ancestral Health Society, and current editor of the Journal of Evolution and Health. Sudhindra (Sud) Rao is one of my graduate students at Binghamton University whose PhD research is focused on ancestral health.

In this inaugural article, we’ll introduce the concept of ancestral health in a conversational tone.

DSW: Aaron and Sud—Welcome to TVOL and thanks for helping me organize this series on Ancestral Health. Please say a little about yourselves and how you became interested in the subject.

APB: I study animal cognition for a living, but about 8 years ago I stumbled upon the paleo diet and related concepts. This was before they were mainstream. In rapid succession I read Gary Taube’s Good Calories, Bad Calories, Weston A. Price’s Nutrition and Physical Degeneration, and then began reading the blogs of Mark Sisson, Stephen Guyenet, and Robb Wolf, among others. I became very curious, and so I started tinkering with low-carb, paleo (or primal) style diets. Although it wasn’t my intention, I lost some weight on the diet. But the most profound changes were to my cognition and health. Up until then, I had been plagued by frequent bouts of “brain fog”, intense irritability when I was hungry, and low energy. These symptoms completely vanished and were replaced by a new vitality and clarity of thought. Continual gut inflammation (bloating) disappeared as well. Perhaps the most amazing result was that, after a year on the diet, a heritable genetic condition called erythropoietic protoporphyria (EPP) went into complete remission. Sufferers of EPP experience painful and burning skin when exposed to sunlight. I had always avoided the sun as a result. But, I discovered that not only did my tolerance to sun exposure increase dramatically, the EPP symptoms completely vanished no matter how much sun exposure I received!

It was these results that led me to delve deeply into the science and practice of Ancestral Health, a term that encompasses ideas about evolutionary mismatch and human health much more broadly than just diet. As an academic, I was discouraged that this framework was not viewed as important, and instead was often denigrated for being “fringe.” The conventional approach of using our understanding of mechanisms of disease to seek new pharmaceutical targets, rather than correcting the source of the problem (mismatch) still held sway. So a colleague of mine (Brent Pottenger) and I decided to establish the Ancestral Health Society and hold an annual Ancestral Health Symposium. The purpose of the symposium is to provide a platform for the open discussion of ancestral health topics for academics, clinicians, and laypeople. We have found the integration of academic and clinical approaches on the one hand, with citizen science with the public’s participation on the other hand, to be a powerful and much needed forum to discuss sustainable approaches to real health change.

Since forming AHS, I have also started the Journal of Evolution and Health of which I’m a chief editor, and have begun research in my lab to study the effect of diet quality (whole foods versus processed foods) on health and cognition using the rat model.

SR: I am a doctoral student working with David at Binghamton University (SUNY) Binghamton, New York. As it often happens in David’s lab, he suggested a book to read over the summer. It was titled Food and Western Diseases: Health and Nutrition from an Evolutionary Perspective by Staffan Lindeberg. A book that I have since read at least 5 times. This was my first foray into the field of paleo-diet studies. I delved into this topic by understanding the hard scientific evidence. Soon afterwards David and I decided to take on the ambitious task of carrying out a dietary trial involving a paleo-type diet. There were (back then) and are (today) only a handful of clinical studies that have tested the ‘paleo diet hypothesis’. We are currently carrying out a test of this hypothesis by recruiting Binghamton University Faculty, Staff and Students in a 12 week dietary study. The field of ancestral health is riddled with arm chair speculations and just-so stories. One personal goal of joining this project is to separate anecdotal evidence from scientific evidence and to present it in an easily accessible manner to the general public.

DSW: Aaron, I knew you when you were a graduate student and I was struck by how different you looked after your dietary shift. Now I’m glad to become involved in this topic area through Sud’s PhD research. Let’s begin by setting the stage broadly. What are some potential mismatches other than dietary mismatches that we might feature in our series?

APB: A mismatch between our ancestral and modern environments in terms of physical activity and natural movement comes to mind as being almost as big a mismatch as is diet. Based on paleoanthropological evidence from hominid fossils, and from the study of individuals living in contemporary hunter-gatherer societies, humans moved around quite a bit and were very active. People in hunter-gatherer groups walk 10s of kilometers a day on average. In addition to this low-level cardiovascular activity, they also lifted and carried very heavy objects, climbed, ran, and jumped. Of course, much of their time was also spent in leisurely activities, sitting, standing, and squatting. A major difference is that they did not do any one of these activities for a very long, uninterrupted time. Rather, the nonlinear stream of behavior consisted of frequent transitions between all of these activities. Rather than running on a treadmill for 45 minutes at a constant pace, an individual might walk at varied paces and on uneven terrain for a while, then stop and squat to inspect something on the ground–the shoot of an underground storage organ, grubs hiding under the leaves of a bush, or animal tracks or other spoor, then get up and sprint quickly for a few minutes to catch up with the rest of the group who continued on ahead. Movement was functional and spontaneous, very different from today’s rigid, static, and unvarying patterns of movement. The implications this shift has on our overall health and wellbeing are just becoming the target of investigation.

We suffer mismatches, too, in so many other facets of our modern lives, ranging from the lack of variation in our thermally-controlled interior environments, patterns of light and dark exposure including limited exposure to the high-intensity of direct sunlight, to the myriad of chemicals that our bodies bath in from all types of environmental sources, to even our social groups and educational and occupational settings.

In fact, one area I’ve become particularly concerned about is how children are raised in the modern educational setting. If you look at how children in contemporary hunter-gatherer societies develop, after about the age of 5 years old, they form stable groups of mixed-age and mixed-gender. They also have much more autonomy than do children in modern society. In modern society, children’s ability to engage in self-guided activities, especially play, are severely restricted. I’ve argued based on evidence from research on cognitive development, brain development, and education that this restriction on free play may have a negative impact on proper social and intellectual development, and on mental health1.

Collectively, these mismatches are thought to be major contributors to our overall disease burden and the slow and steady decline and degeneration as we age. They also likely contribute in a major way to psychological and mood disorders, especially anxiety and depression.

SR: I would like to continue where Aaron left off. Mental health in general and anxiety and depression in particular are especially relevant to mismatch studies. Anxiety is adaptive in its proper environmental context. A school of timid/anxious fish are more likely to survive than a school of fish that are bold or unnaturally calm and zen-like while facing danger. Acute stress or anxiety response has played a critical role in evolution of life forms. However, acute anxiety or a stress response is energetically very costly, like any other adaptation it comes with trade-offs. If environmental factors trigger a chronic activation of the stress response then this could lead to deleterious health effects. Chronic stress has been linked to increased obesity by seeking comfort foods in rats and metabolic disorders in humans2,3.

Another novel and very relevant area of human mismatch studies is the gut microbiome. Humans are essentially multicellular eukaryotes and the gut microbiome is mostly bacteria and archaea. The relationships between these two groups of organisms are ancient. Some of these relationships may have evolved even before mammals first appeared. Diet is a very strong determinant of the composition of the gut microbiome in all animals. Since the split of human lineage from the chimpanzees there has been a general reduction in the diversity of gut microbiota. This reduction probably occurred hand in hand with changing dietary habits. The general trend over the past 7 million years indicates a shift from fibrous, tough plant foods to hard and brittle foods, to a very a broad diet that included, plants, tough foods, hard foods, meat, seafood and underground storage organs. The reduction in diversity may have occurred as a result of deviation from a plant based diet. Microbes are critical in digesting otherwise indigestible plant fibers.  As anatomically modern humans began to rely on cooking, and high quality foods such as meat and underground storage organs, a diverse gut microbiota was no longer needed. As our diet came to rely even more on processed and refined foods the diversity of gut microbiome continued to reduce. Is this reduction in diversity a consequence of mismatch between bacteria and their environment (the food we eat and feed them)?

DSW: What Aaron says about child development is HUGE and eloquently expressed by Peter Gray in this article published in AEON, his book Free to Learn, and his Freedom to Learn blog at Psychology Today. And there are still more potential mismatches, such as endocrine disruptors, overly hygienic environments that disrupt our immune systems, and on and on. Some are in front of our faces–literally–such as the glasses we must wear to correct for myopia. Recently I learned that nearly 100% of us have abnormal jaw development. What’s normal is for our upper and lower front teeth to meet rather than the upper teeth coming in front of the lower teeth. If we spent as much time chewing on hard things as our ancestors, we wouldn’t need our wisdom teeth pulled and our front teeth wouldn’t be crowded.

To conclude our inaugural conversation, I’d like to focus on the frequent accusation that mismatch hypotheses are “just-so stories” and that efforts to improve our health based on the mismatch concept, such as the Paleo Diet and CrossFit, are scientifically unsupported fads, not least because there is money to be made by promoting them. How can we separate the wheat from the chaff when it comes to testing mismatch hypotheses?

APB: You hit on the major problem facing ancestral health as an academic discipline. A “just-so” story, by definition, is one that is incredibly difficult or impossible to test. It is not falsifiable. The paleo diet and ancestral health approaches, on the other hand, are eminently testable and easy to falsify. Evolutionary Mismatch (EM) theory provides a framework for making specific hypotheses that in turn lead to testable predictions. It can be tested in any organism for which we have decent knowledge of their natural environment and ecology. Even fruit flies, when switched from a recent laboratory diet back to their natural diet have been shown to have extended health and life 4.

To be an acceptable science, EM theory must start with the natural ecology of the species in question. We actually have a remarkable amount of knowledge of the lifeways of contemporary hunter-gatherer societies, living as close as we can imagine to our ancestral ecology. We also have gleaned many clues from the historical, archeological, and paleoanthropological literatures on our ancestral ecology and environment. We know that modern hunter-gatherers living an ancestral lifeway show very little chronic and degenerative disease. It is from this groundwork on ecology and evolutionary history that we can formulate specific hypotheses of EM for testing. Kuipers et al. and Lindeberg provide exemplary accounts of the many clinical successes that have emerged from EM theory 5,6.

Thus, the evidence speaks against calling EM theory a “just so” story. Of course, many of the details are likely wrong—as is true with all science. And many statements or claims about the paleo diet are likely mischaracterized, sometimes for financial gain. But these problems occur in any scientific discipline, especially one concerning such an important topic relevant to the health and livelihood of every individual and to modern society’s most pressing issues. It means that we must be extra cautious when making academic claims, and use logic and evidence and a critical eye to evaluate such claims. Science is a self-correcting discipline, and over time and a lot of empirical and theoretical work, comes closer to the truth, and yields many insights along the way. The science of EM theory and Ancestral Health are perhaps the most relevant to society today and likely have the greatest chance of success at improving today’s most pressing problems.

SR: The primary reason why ancestral health and ‘paleo-diet hypothesis’ is susceptible to ‘just-so’ stories is because it is very easy to build stories and apply natural selection based explanations to justify one’s thinking. The line of thinking has the following logic. ‘X’ is an anomalous trait that is harmful to humans. How is it that natural selection has not eliminated ‘X’ if it is detrimental to human health? It must be that ‘X’ either has adaptive function today or was adaptive in the past. It persists today because natural selection has not had ‘enough time’ to minimize its frequency.

There is nothing wrong with this line of thinking–as long as the hypotheses that it generates can be tested–but it’s false to assume that natural selection is the only cause of evolution, as Stephen Jay Gould and others were careful to stress. Other major mechanisms of evolution include genetic drift, migration, mutation and developmental factors. In fact Endler and McLellan have named more than 10 evolutionary processes7! A fully rounded evolutionary approach asks ‘what factors account for the form and distribution of this trait?’ including but not restricted to natural selection8. Such an approach has been rarely applied to human health. I will show how it can be applied to the topic of obesity in my first article for the series.

DSW: Right! My own take is is that “just so story” is just another phrase for “untested hypothesis”. Some mismatch hypotheses are so obvious that they scarcely need testing, such as baby sea turtles heading toward beach houses and the fatal attraction of aquatic insects to man-made reflective surfaces. Other mismatch hypotheses are much more difficult to test, especially when the phenotypic trait is complex (e.g., a human disease) and information about the ancestral environment is fragmentary (e.g., the distant human past). Just because a hypothesis is difficult to test, however, doesn’t mean that it lacks utility! The concept of mismatch is very important for organizing research, no matter how easy or difficult the hypotheses are to test.

The next article in our series, by Aaron, is a good case in point. A recent scientific study that has been widely reported as debunking the paleo diet is itself highly flawed and misinformed about the concept of mismatch. The quality of the science needs to be evaluated on both sides.

Thanks, gentlemen! I look forward to exploring this important topic for a large audience with your help.


  1. Blaisdell, A.P. (2015) Play as the Foundation of Human Intelligence: The Illuminating Role of Human Brain Evolution and Development and Implications for Education and Child Development. Journal of Evolutionary Health, 1(1):1-54.
  2. Chandola, T., Brunner, E., & Marmot, M. (2006) Chronic stress at work and the metabolic syndrome: prospective study. BMJ, 332: 521.
  3. Dallman, M. & Pecoraro, N. (2003) Chronic stress and obesity: a new view of “comfort food.” PNAS, 100(20) 11696-11701.
  4. Rutledge, G. & Rose, M. (2015) An Evolutionary Analysis of Healthspan Extension Using Diet: Have We Come to the End of the Ponce de Leon Trail? In A. Vaiserman, A. Moskalev and E. Pasyukova (Eds.) Lifespan Extension. Lessons from Drosophila. Berlin, Germany: Springer.
  5. Kuipers, R.S., Joordens, J.C.A., & Muskiet, F.A.J. (2012) A multidisciplinary reconstruction of Palaeolithic nutrition that holds promise for the prevention and treatment of diseases of civilisation. Nutr Res Rev. 25(1):96-129. doi:10.1017/S0954422412000017.
  6. Lindeberg S. (2010) Food and Western Disease: Health and Nutrition from an Evolutionary Perspective. Oxford: Wiley-Blackwell.
  7. Endler J, McLellan T. (1988) The process of evolution: Toward a Newer Synthesis. Annu Rev Ecol Syst. 421:395-421.
  8. Lloyd E. (2015) Adaptationism and the Logic of Research Questions: How to Think Clearly About Evolutionary Causes. Biol Theory.

Published On: March 24, 2016

Aaron Blaisdell

Aaron Blaisdell

Aaron Blaisdell is a Professor in Learning & Behavior and Behavioral Neuroscience in the UCLA Psychology Department. He presides over the Comparative Cognition Lab, studying cognitive processes in rats, pigeons, hermit crabs, and humans. He is also interested in how human ancestry and evolution can inform us about health and well being in the modern world, and is currently studying the interaction between diet and cognition. He is a founding member and Past President of the Ancestral Health Society, Past President of the International Society for Comparative Psychology, an Editor-in-Chief of the Journal of Evolution and Health, and a member of the Brain Research Institute, the Integrative Center for Learning & Memory, and the Evolutionary Medicine program all at UCLA.

Sudhindra Rao

Sudhindra Rao

Sudhindra Rao is a doctoral candidate at Binghamton University (SUNY) studying human health and nutrition, in particular the paleo diet.  

David Sloan Wilson

David Sloan Wilson

David Sloan Wilson is SUNY Distinguished Professor of Biology and Anthropology at Binghamton University. He applies evolutionary theory to all aspects of humanity in addition to the rest of life, both in his own research and as director of EvoS, a unique campus-wide evolutionary studies program that recently received NSF funding to expand into a nationwide consortium. His books include Darwin’s Cathedral: Evolution, Religion, and the Nature of Society, Evolution for Everyone: How Darwin’s Theory Can Change the Way We Think About Our Lives, and The Neighborhood Project: Using Evolution to Improve My City, One Block at a Time and Does Altruism Exist? Culture, Genes, and the Welfare of Others. .

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