Premise

hadazbe-returning-from-hunt-smallThe human body – with its genome and microbiome – was shaped through millions of years of evolution.

As humans, we tend to accept the world around us as “normal”, but from an evolutionary perspective, today’s living conditions are abnormal and novel. When looking back at the human evolutionary journey it quickly becomes clear that the world around us has changed dramatically in a very short time.

For 99.5% of the evolutionary history of our genus (Homo) we lived as hunter-gatherers; a way of life that dominated up until the agricultural revolution approximately 10.000 years ago (1).

Although our milieu has changed dramatically since our days as hunter-gatherers, our ancient genome is still largely with us; a genetic make-up that is poorly matched with contemporary diets and lifestyles.

Evolutionary mismatches

The ancestral natural environments in which the human genome was shaped for millions of years via natural selection – the process by which individuals best adapted to the conditions under which they live tend to pass on more of their genes than those that are less well adapted – differ markedly from modern environments. In the Paleolithic era (2.6 million years ago – 10.000 years ago), hominins lived together in small groups that subsisted on wild plants and animals, and during this time, heritable traits that improved our ancestors ability to survive and reproduce as hunter-gatherers were positively selected for.

The agricultural revolution marks the beginning of substantial changes to our living conditions – changes that have accelerated in pace and force over the last couple of centuries. 10.000 years is just a blink of an eye from an evolutionary perspective, and many of the lifestyle transitions have been too powerful and/or too recent for our bodies to adapt. From a genetic perspective we are still largely Stone Agers, meaning that cultural evolution has vastly outpaced biological evolution (2, 3, 4).

Since our biology has not been able to keep up with the rapid changes to our environment over the last several millenia, we now experience a gene-environment mismatch (1, 5). In the modern world most of us subject our bodies to stimuli that fall in the category of being too much, too little, or too new, and as a result, evolutionary mismatches present themselves.

When the human body is subjected to a lifestyle for which it is poorly adapted, the human genome responds with a suboptimal gene expression pattern (1, 6). The second genome associated with the human body – the Human Microbiome – is also altered in such a ways that incompatibilities between the human genome and the human microbiome occur (7, 8, 9).

All of this results in a suboptimal phenotype and diseases of civilization – such as type-2 diabetes, acne vulgaris, heart disease, and colon cancer – that are rare or nonexistent among hunter-gatherers and traditional people who follow a diet and lifestyle that are better matched with our ancient genome (1, 10). These peoples live in environments that more closely resemble those we evolved in for millions of years.

10 diseases caused by evolutionary mismatches

The number of mismatch diseases that affects contemporary people is staggering. Virtually every human alive today will develop some type of mismatch disorder during his/her life. The infographic below focuses on a small subset of the diseases of civilization, some of which are very prevalent in industrialized societies.

mismatch-diseases

Combining the best from both worlds

The average lifespan of hunter-gatherers and other native populations is relatively short compared to today’s standards in many industrialized nations, but that’s not due to high cancer rates and cardiovascular diseases, but rather because of little access to modern medicine (11). In western societies, public health advancements have given us the opportunity to profoundly decrease infant mortality and prolong the lives of old and sick people. We live longer, but we aren’t healthy.

Also, the fact is that when we look at the life expectancy of an adult hunter-gatherer, the stereotypical image of nasty, brutish, and short lives doesn’t reflect reality. A compilation of data on hunter-gatherer societies suggest that modal age of adult death is about seven decades (adaptive life span of 68-78 years), and contrary to most westerners, these people tend to be healthy all the way up to old age (12).

Nobody’s denying that many of the medical-, technological-, and cultural-advancements since the Paleolithic era have dramatically reduced rates of infant mortality, helped us overcome many infectious diseases, and made our lives easier and better in several ways. Few people would probably say that they’d like to leave the comforts of modern life behind and return to a forager lifestyle – and that’s not the point either. The point is to realise that we’re still – to a significant extent – adapted to live in the various and diverse ancestral environments we evolved in as hunter-gatherers, sometimes referred to as the Environments of Evolutionary Adaptedness.

The etiology, prevention, and treatment of the diseases of civilization: A Darwinian conceptual framework

conceptual-framework-diseases-of-civilization

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