What makes for a healthy body? This question is at the core of all health-related endeavors, ranging from nutritional research to clinical medicine to personal training. Much attention is devoted to how different types of stimuli and exposures – nutritional elements, medications, exercise practices, and so forth – presumably affect our well-being and consequently how we should live our lives to attain truly good health.
Not much attention is devoted a more basic question of health though, namely the question of whether we’re designed to be healthy. That’s extremely unfortunate, as that question precedes the former one in the line of exploratory questioning that’s the most reasonable in the context of health and medicine.
If we haven’t posed that question or haven’t got a clue what the correct answer to it is, we’re bound to get into a lot of trouble and experience feelings of confusion and bewilderment during our search for answers to the other question. On the flip side, if we have managed to answer it, or at least made some headway in that respect, we’re in a good starting position in the health and medical game, as we’ll be equipped with information that’s required to understand where one should ideally direct one’s focus in the search for health.
Would natural selection be expected to produce healthy organisms?
We’re all products of an evolutionary process; hence, it follows that the key to answering the question posed in the title of this article must lie somewhere in the realm of evolutionary science. Historically, evolutionists have devoted fairly little attention to the role that health plays in evolutionary processes. Some have even dismissed it as being largely insignificant with respects to Darwinian selection. This is something you’ve probably noticed if you’ve delved into evolutionary science, including some of the many review articles on Darwinian/evolutionary medicine that has come out over the most recent decades.
Some investigators have a habit of ignoring health-related aspects of evolution altogether or expressing the idea that organismal health and wellness are largely irrelevant in the context of biological evolution. All that matters is survival and reproduction. This has been repeated so many times that it’s become a sort of mantra within certain circles. At first, this notion seems to hold a lot of truth; however, upon closer inspection and careful thought, it becomes clear that it’s impetuous to so quickly push health to the side.
Nobody’s denying that it’s ultimately one’s reproductive success that matters when it comes to the passing of one’s genes, and hence, the evolutionary legacy that one leaves behind. What’s important to recognize though, is that there are multiple advantageous to being healthy and robust, as opposed to frail and sick, in the struggle to survive and reproduce; hence, natural selection would be expected to produce well-functioning organisms as a “by-product” of favoring traits that are beneficial in the context of reproductive success, particularly under natural conditions.
The following quote, derived from a fascinating paper entitled What is the ultimate cause of socio-economic inequalities in health? An explanation in terms of evolutionary psychology, draws attention to this aspect of evolution…
Human psychology has been designed, by natural selection, to promote reproductive success but health is one of the pre-requisites for such reproductive success. Health is, thus, a by-product of natural selection, insofar as reproduction can only occur when a certain minimum level of adult health has been reached. In consequence, humans have a rich inbuilt repertoire of health promoting or salutogenic mechanisms selected for their capacity to maintain organismal integrity at least until the time of reproduction. These range from the most basic level of organization (such as the mechanisms for repair of errors in DNA transcription, inter-cellular control mechanisms, and the processes of organism-wide homeostasis such as the immune, endocrine and nervous systems) up to the vast range of cognitive processes extending from simple protective reflexes to content-specific social learning. Without this innate set of processes the endemic hazards associated with human life would render survival until reproductive age extremely unlikely. (1)
A depiction of why health matters in evolution
Here on the site, I’ve talked at length about the link between organismal health and fitness, pointing out that there are a number of different reasons why health matters in evolution. So as to illustrate this concept, I’ve created an infographic that depicts the 6 major reasons I’ve pinpointed to date…
The aforementioned insights help explain why nature, including its complex and varied life, is full of vigor
If you’ve ever paid attention to the characteristics and workings of nature, you may have noticed that it appears very well designed, in the sense that its different parts appear to fit seamlessly together, forming a beautiful whole. Furthermore, it appears to be full of life, vigor, and energy. This is truly magnificent. It’s not surprising though, in light of the aforementioned discussion. Not only would life be expected to propagate and become naturally organized, but organisms would generally be expected to display vigor and health.
Here on Darwinian-Medicine.com, I’ve talked at length about the physical condition of animals that live under natural conditions. The primary focus has naturally been on Homo sapiens sapiens, as that is the species that we belong to and are the most concerned about. What’s important to recognize though, is that we are no different from other organisms with respects to the types of pressures that shaped the way we are designed and function. We too are products of evolution via natural selection.
In my articles, I’ve covered research showing that humans who live under natural, Paleolithic-like conditions tend to be lean, physically fit, and free of diabetes, cancer, myopia, heart disease, acne vulgaris, and a number of other diseases and health problems. This may seem surprising and irregular in light of the fact that all of these conditions are extremely common in most modern societies. What becomes clear though, as one starts to examine things under evolutionary light, is that it’s the latter situation that’s irregular, not the one that exists in nature.
It’s not really surprising that hunter-gatherers are lean and free of all of the aforementioned disorders, as the listed conditions would all be expected to impair one’s ability to survive and reproduce, especially under natural, non-industrialized conditions. A hunter-gatherer suffering from diabetes or cancer would obviously be at a disadvantage when it comes to food procurement, kin provisioning, and the like. Myopia and heart disease would also be expected to undermine survival and reproduction under natural conditions, as hunter-gatherers rely on good eyesight and cardiovascular functioning to effectively do some of the things they need to do to survive. Finally, acne vulgaris, a symptom of highly insulinogenic nutrition and microbiota disturbances, among other things, undermines one’s ability to attract healthy, fertile mates. Hence, it is to be expected that these types of health disorders are rare in the wild, not just among humans, but also among other species, and not just because of potentially high infant mortality rates, which would be expected to reduce the number of frail or “weak” organisms in a population.
It’s only when genes are subjected to an environment that differs from the one for which they were selected that sickness may become the norm, whereas healthiness could end up becoming the exception. In such a scenario, natural selection would be expected to “work on” bringing the organismal state towards a healthier state by favoring the genes of the organisms that do best, health wise, under the new conditions. The degree of change that is brought about will largely depend on the fitness implications of the relevant diseases and health problems, as well as the current rate of environmental change.
This is not only true within the animal kingdom; it applies to the entirety of the ecosystem of the Earth. The evolution of plants would be expected to conform to similar types of principles as the ones described in the infographic shown earlier, although one would obviously have to account/adjust for the fact that plants differ from animals in many respects. Bacteria, fungi, and archaea are even more dissimilar; however, even within those domains, “health” could be said to be important in evolutionary contexts.
With all of that being said, one shouldn’t expect all organisms that live in their respective “environment of evolutionary adaptedness” to be perfectly healthy. There are many reasons why this is the case. First of all, all organisms take part in a never ending arms race. Sometimes, one or more life forms may evolve new capabilities or “weapons” that give them an evolutionary edge over certain other life forms, in the sense that they gain a competitive or exploitative advantage. This is particularly relevant when talking about relations between small and large organisms, such as for example microbes and humans, as smaller organisms, in particular unicellular life forms, evolve at a very different pace than larger ones.
Secondly, abiotic environmental conditions – climate, temperature, and the like – are always going to fluctuate somewhat. This can obviously affect organismal health and vitality. Thirdly, natural selection will favor genetic variants that are beneficial in the context of reproductive success, even if they are detrimental in the context of health at some point during the life cycle. Fourthly, the constant mixing of genes and mutational events that take place in evolution can have detrimental consequences. Last but not least, there’s a chance element and adaptive range to evolution. Irrespective of how careful and robust one is, one’s safety – against for example predators, parasites, or moving vehicles – isn’t guaranteed.
A healthy dose of health could do wonders for evolutionary medical science
The fact that health is often ignored or dismissed as being largely insignificant in evolutionary contexts is bound to generate a trail of problems. First of all, it’s bound to bring about a lot of misinformation and confusion pertaining to the health-related outcomes and implications of evolution, which translates into unnecessary or misdirected research and use of resources. Personally, I’ve spent many years thinking about issues pertaining to the role that health plays in evolution and the question of whether we’re designed to be healthy. Part of the reason why this is something that’s taken up much of my time and evoked much mental dubiety and contemplation is that the relevant scientific literature features many conflicting statements and ideas. Whereas the work of some authors gives the impression that health fortification has historically been a key part of Darwinian adaptation, and consequently that we would be wise, from a health standpoint, to adjust our way of life on the basis of insights gleaned about the conditions of life in our environment of evolutionary adaptedness, others’ work is dismissive of health. Perhaps needless to say, I’ve come to believe that the former view is the one that best conforms to reality.
Secondly, as a consequence of the above, it’s bound to severely impede health and medical-related progress and practise and cause much unnecessary suffering, for the simple reason that it’s very difficult to fully make sense of pretty much anything that has to do with health or medicine if one doesn’t possess information about the health-shaping properties of natural selection. If it had been more widely recognized that health matters in evolution, evolutionary science would undoubtedly have been more widely incorporated into medicine, nutrition, and health sciences, because implicit in the realization that organismal health is of critical importance in evolutionary processes is the realization that evolutionary insights should be a cornerstone of all health management and promotion. It suggests that disease isn’t necessarily inherent to the organismal design, but rather is likely to occur as a result of incompatibilities between the design and the milieu of the organism. By “working our way backwards” and exploring the environmental conditions under which we evolved, we immediately get a better understanding of not only why we get sick, but also where we should ideally focus our efforts in order to prevent and treat illness.
It’s often assumed that health, as it relates to the physical condition and well-being of organisms, is largely irrelevant in biological evolution, seeing as it’s ultimately reproductive success, not health, that matters when it comes to gene survival. At first, this assumption may come across as being reasonable, in part because we humans are currently in a situation of ill health, with a number of diseases and health disorders, including breast cancer, irritable bowel syndrome, myopia, ischemic heart disease, osteoporosis, and acne vulgaris, running rampant in many parts of the modern world.
However, following greater scrutiny, it becomes clear that this public health situation is highly irregular, representing an extreme case of evolutionary mismatch, and that natural selection would be expected to preserve and advance healthiness, while continually weeding out sickness, particularly under natural conditions, for the simple reason that it’s generally a major advantage, in the context of reproductive fitness, to be healthy and robust as opposed to sick and frail. This is not to say that a gene variant that’s beneficial in the context of reproduction while somehow harmful to health sometime during the life span won’t be favored; however, in general, it’s safe to say that there’s a marked connection between health and fitness in Darwinian evolution. By acknowledging that this is the case, we immediately get a better understanding of where we should ideally direct our focus as we search for ways to generate health and vigor.