Every living thing on this planet is a product of evolution via natural selection. This is important to recognize, as it is the principle piece of information that one needs in order to make sense of how the world works: why organisms look and behave the way they do, how and why populations change over time, and what sculpts the global ecosystem. Furthermore, an appreciation of the (r)evolutionary concept Darwin first presented to the world some 150 years ago is required to understand why disease exists, how it develops, and how it can be effectively prevented and treated.
Evolutionary mismatch theory explained
Populations change over time as a result of the selective pressures they face. Those organisms that are best adapted to the current conditions of existence send more genes, in the form of offspring, into the future than those that are less fit, and as a result, the population evolves over times.
If the environment stays fairly stable over a long period of time, there will be ample time for natural selection to fine-tune the physiological systems of the relevant life forms so that they are well-suited to the conditions of life, which encompass everything from water and nutrient availability to the presence of sunlight and predators. What’s important to recognize though is that abiotic conditions are always going to fluctuate somewhat and that all life forms evolve and take part in a battle for existence. Hence, life is never at a stand-still; natural selection is always working.
Given that organisms are “designed” for a particular milieu, it follows that environmental change can bring about a mismatch between the design of the organisms and the environment. The severity of this mismatch will depend on the pace of the change, as well as the extent of it. If the environment changes profoundly in a short period of time, the mismatch will be severe.
Whether or not natural selection will resolve the various aspects of this mismatch situation depends on the impact they have on the relevant organisms’ reproductive success. If the mismatch triggers a profound selection pressure and major inter-individual disparities with respects to reproductive success, the population will change fairly rapidly; however, if the effects on reproductive success are more subtle, then biological change will be slow.
In both cases, however, the mismatch situation will affect the functionality of the relevant organisms. This really goes without saying, seeing as the organisms now find themselves in an environment that differs from the type of environment that they are “designed” for. In nature, there’s an intimate relationship between health and reproductive success, in the sense that organismal health status greatly influences organismal reproductive success. Healthy organisms typically have a better chance of getting a hold of food, forming beneficial social bonds, and evading and combating predators and pathogens, and they have a higher libido and are more reproductively robust than unhealthy organisms. In other words, even though reproductive success is the only thing that natural selection ultimately “cares about”, it ends up being a health-shaping force nonetheless.
This is important to recognize, as it automatically generates several reasonable assumptions regarding health and medicine that can be appraised via scientific investigations. First of all, it implies that the majority of organisms that reside in an environment that has remained fairly stable for a long period of time are going to be relatively physically robust and healthy. This has been shown to be the case. For example, it has been shown that hunter-gatherers are lean and metabolically fit and largely protected from cancer, and have well-developed facial structures and excellent eyesight, among other things.
Secondly, it implies that when organisms are subjected to an evolutionary mismatch situation, their health will be affected. This has also been verified by modern science. Countless scientific experiments and investigations show that when organisms are subjected to conditions that differ markedly from the conditions under which their biology was shaped, their health deteriorates (e.g., 1, 2, 3, 4, 5, 6, 7). In order to improve or restore the health of the organisms, one has to adjust their milieu and way of life so that genome-environment mismatches are partly or fully resolved.
This should arguably be the foundational truth upon which we construct our modern health and medical system!