In part 1 of this series on evolution and human health we established that millions of years of evolutionary pressure shaped the human body, from musculoskeletal system, to metabolism, to brain function, and that Africa is the birth place of Homo sapiens. In part 2 we continued with our species’ journey out of Africa approximately 70.000 years ago and discussed how humans were able to adapt to new living conditions around the world.
In this last part of the 3-part series we’re really getting into the main points of these articles. Homo sapiens sapiens is a very young species, but what we have to remember is that even though our species is only about 200.000 years old, our genus, Homo, has been around for approximately 2.3 to 2.4 million years. Why is this important to know? Because it shows us that the ~10.000 years that have passed since the Agricultural Revolution is just a drop in the sea compared to the millions of years we lived as hunter-gatherers. This is even more true if we look at the Industrial Revolution, which only represents 7 of the 76.667 generations our genus has been around (1).
A new way of life
Although the climate changes, dietary shifts, colonization of new parts of the world, etc. discussed in part 1 and 2 of this series all had a major impact on our hunter-gatherer ancestors, it could be argued that the most dramatic change didn’t come until the Agricultural Revolution approximately 10.000 years ago. For millions of years, hominins lived in small tribes that subsided on wild plants and animals, but with the domestication of plants and animals, humans started settling down in larger communities and moving towards a more modern way of life.
While it could be argued that this transition brought with it many good things, there were definitely also downsides, especially related to human health. These downsides include increased mortality from infectious disease, a shortening of stature (at least after a while), more tooth decay, and a general decrease in health (1, 2, 3, 4, 5).
Besides the impact of the new, unsanitary living conditions, the nutrition transition that accompanied the Agriculture Revolution was an especially important contributor to this declining health condition:
Generally, in most parts of the world, whenever cereal-based diets were first adopted as a staple food replacing the primarily animal-based diets of hunter-gatherers, there was a characteristic reduction in stature [4, 17–19], an increase in infant mortality [19, 20], a reduction in lifespan [19, 20], an increased incidence of infectious diseases [19–22], an increase in iron deficiency anemia [19, 20, 22], an increased incidence of osteomalacia, porotic hyperostosis and other bone mineral disorders [4, 19, 20, 22] and an increase in the number of dental caries and enamel defects [19, 20, 23]. In a review of 51 references examining human populations from around the earth and from differing chronologies, as they made the transition from hunter-gatherers to farmers, Cohen  concluded that there was an overall decline in both the quality and quantity of life. (4)
For millions of years, a forager existence had been the norm, and selective pressures had shaped a genome that now stood face to face with a different environment. As for the microbiome, the long co-evolution of man and microbe had fine-tuned a close relationship. What happened with agriculture? Hard data are clearly hard to come by, but a few educated guesses give us several hints. With exposure to a different microbial environment (5) and consumption of a new grain-based diet, the microbiome would have shifted. Although all of the microbes we carry with us can be thought of us as part of our body, they are also very much a part of our environment. So, just like our survival in a specific place depends on things like our ability to procure food, survival also depends on our adaptation to the microbial environment in and around us. This is clearly seen in the case of infectious diseases, but it also in many ways apply to the symbiotic relationship we have with microbes in general.
Overall, the literature strongly suggests that many markers of human health took a hit with the advent of agriculture – and as briefly discussed, this is really the expected response. Have we ever caught up? Not really. From an evolutionary perspective, 10.000 years is just a blink of an eye, and there’s no doubt that we’re still – to a significant extent – adapted to a Paleolithic way of life. That’s not to say that we haven’t evolved since then. Lactase persistent alleles have been selected for in many parts of the world, infectious diseases have driven genetic adaptations, and our gut microbiome has changes, among other things. However, as we know, a forager lifestyle is still deeply rooted within our genes.
Fossil fuel, artificial lighting, and fast food
If the transition that came about with the Agricultural Revolution was bad for human health, it’s nothing compared to the changes that have occurred over the last couple of centuries – and especially the last couple of decades, as wild meat, natural circadian rhythms, and daily exercise have been replaced with fast food, sleep deprivation, and video games.
An ancient genome and physiology that collide with a modern lifestyle is no pretty sight; with everything from acne vulgaris, to lower back pain, to cardiovascular disease, to obesity being the manifestation of an evolutionary mismatch (1, 6). That’s not to say that all of the health problems we experience in the modern world are mismatch conditions, but as Dr. Dan Lieberman, Evolutionary Biologist at Harvard University, says:
I don’t think it is possible to overemphasize just how important mismatch diseases are. You are most likely going to die of a mismatch disease. You are most likely to suffer from disabilities caused by mismatch diseases. Mismatch diseases contribute to the bulk of health-care spending throughout the world. (5)
As for the microbiome, the western lifestyle – with its antibiotics, hand sanitizers, refined food, and caesarean sections – selects for a very different microbiota than the one our ancestors carried around. For millions of years we developed a close relationship with bacteria, archaea, and other microorganisms; a relationship that is now being put to the ultimate test. Eubiosis has for many turned into dysbiosis, which is especially concerning since the amount of studies linking dysbiosis to human disease is growing steadily every day.
What about Darwinian fitness? In part 2 I said that physical fitness and Darwinian fitness in an ancestral natural environment were closely linked. This is no longer the case. Modern medicine and technology have allowed us to combat infectious diseases and decrease infant mortality substantially (at least in the industrialized world); thereby buffering for the effects of many of the selective pressures that worked on the human genome for millions of years. In combination with the fact that we don’t really need even modest levels of physical fitness to be able to survive and reproduce in the modern world (no need to hunt for food when you have a grocery store down the street), this has led to a completely new condition of life. Natural selection is still in the works, and we’re still evolving, but it’s not like in an ancestral, natural environment where those who were not fit enough to survive past infancy, procure food, and escape dangerous animals would have died out.
That’s of course not to say that decreased infant mortality, low rates of infectious disease, and easy access to food are necessarily bad things. It’s just that we should take a step back and question how these aspects of our life impact the bigger picture of things. Competition – both between species and within the same species – drives evolutionary change; those who are best adapted to their environment have a better chance of passing on their genes. What happens when we turn everything upside down?
There are many positive aspects to life in the modern, industrialized world. We’ve created living conditions that are very “comfortable”, and there’s no doubt that many of the recent technological, economic, and medical advancements have made our lives better in many ways. However, when it comes to physical fitness and degenerative disease, the picture is not so joyful.
Acne vulgaris, asthma, obesity, type-2 diabetes, heart disease, and many other chronic disorders that are highly prevalent in the world today are manifestations of a mismatch between genes and environment. An evolutionary perspective on health and diseases shows us that looking for drugs, vaccines, or “cures” for these conditions shouldn’t be our primary focus. Instead we should look for ways to adjust our lifestyle so it is compatible with our biology. That’s not to say that we don’t need modern medicine or can’t enjoy some of the comforts of modern living, it just means that we should always keep in mind that we are still – to a significant extent – Stone Agers from a genetic perspective.
A video that explains the concept of evolutionary mismatch
Prefer watching a video? In the presentation below, Professor Stephen C. Stearns at Yale University gives you an overview of what the concept of evolutionary mismatch is all about.