One of the most common and pernicious misconceptions about evolution is that health is somewhat irrelevant to Darwinian selection. All of the focus is placed on reproductive success, whereas parameters related to organismal health, vitality, and well-being are largely ignored. Even some experienced researchers operating within the realm of Darwinian/evolutionary medicine operate in this manner, which I find concerning, as I think it hinders the search for truths and the advancement of the field. Moreover, it has major public health implications.
The health-shaping properties of natural selection
The major fallacy of the above doctrine is that it doesn’t account for the fact that organisms’ fitness is greatly affected by their health. In other words, even though it’s reproductive success that ultimately matters in evolution, health ends up being a very important factor. One doesn’t have to be a genius to understand that this is the case; all one has to do is to consider how organisms function and behave…
I’ve previously pinpointed and talked about five major reasons why health matters in evolution here on the site, placing a particular emphasis on Animalia. The first one is that healthy and physically robust organisms generally stand a better chance of getting a hold of food, evading predators, quashing pathogens, and otherwise doing what’s required of them to survive than frail, weak, and/or sick organisms. The second reason is that healthy organisms tend to have a higher libido and be more fertile; the third one is that we find signs and manifestations of good health attractive; the fourth one is that healthy organisms are better able to support their kin; and the last one is that healthy organisms require less sleep and rest. Even small advantages and variations can make a significant difference in these regards, which clearly highlights the fact that natural selection is a major health-shaping “force”.
In this article, I thought I’d briefly talk about a sixth reason, which is that it’s better to be healthy than sick in the context of energy allocation and efficiency.
The evolutionary importance of energy optimization
The nutritional distribution pattern and requirements of healthy organisms differ from those of sick organisms. There are primarily two reasons why that is. The first one is that the physiological irregularities of the latter may affect their nutritional needs as a by-product of affecting their internal state. The second one is that the fact that illness tends to have fitness costs means that it has to be dealt with. Resources have to be put into resolving it.
This is particularly true if marked immune activation is required (which it often is, as the immune system is centrally involved in bodily defense), for the obvious reason that energy is required to support immune processes (e.g., cytokine production). This is clearly seen in cases of human illness involving inflammatory responses, as inflammation goes hand in hand with markedly increased use of protein and glucose by the immune system, as highlighted by the quote below:
During infection/inflammation we deal with the metabolic needs of an activated immune system for acute survival. The inactive immune system consumes about 23% of our basal metabolism, of which as much as 69% derives from glucose (47%) and the glycogenic amino acid glutamine (22%). Upon activation, the energy requirement of our immune system may increase with about 9–30% of our basal metabolic rate. In multiple fractures, sepsis and extensive burns, we deal with increases up to 15–30, 50, and 100% of our basal metabolism, respectively. (1)
Basically, upon detection of noxious stimuli, the body mounts strong and potent immune defenses. These defenses aren’t cheap; hence, the issues they were generated to repel should preferably be resolved as quickly and effectively as possible. In that sense, it pays to possess a smooth system that’s capable of rapidly and efficiently dealing with the dangers (e.g., pathogenic bacteria) and complications (e.g., wounds) that one is likely to face on one’s journey through life.
This becomes particularly apparent in light of the fact that illness and inflammation lead to redistribution of energy, away from organ systems involved in reproduction and movement towards apparatus dedicated to defense and healing. Given that resources is reallocated in this manner, it’s not surprising that inflammation-related disease goes hand in hand with muscle wasting, a loss of libido, and sexual dysfunction (2, 3, 4). Nor is it surprising that sick people aren’t as vigorous/energetic as healthy folks. This is obviously relevant in the context of Darwinian fitness, as it’s a lot better to virile and prolific than tired and spiritless for purposes of survival and reproduction
The fact that illness prompts energy reallocation and rest/inactivity helps explain why disease doesn’t always bring about elevations of total energy needs (5). The relative use of calories on processes related to immune function, tissue repair, and the like obviously goes up though – calories that could otherwise (in the absence of illness) have been used for something else. This has evolutionary implications, as energy, in the form of nutrients such as glucose, long-chain fatty acids, and protein, is hard to get a hold of in nature.
Most organisms on this planet are in a very different situation than obese westerners. The challenge they face isn’t to keep a lid on the number of calories they take in, but rather to get a hold of enough energy to survive. It’s only very recently that we’ve altered the conditions of existence in such a way that some organisms (e.g., humans living in industrialized environments, certain domesticated animals) have gotten the opportunity of gorging on energy-rich foods. This is to say that in general, one would expect organisms that get the most bang for each calorie they take in to have a fitness advantage.
This not only means that organisms that use relatively little energy on disease-related processes would generally be expected to be more likely to survive and reproduce than organisms that have to devote a substantial amount of resources to counteracting and overcoming illness, but also that energy optimization in general is important. Organisms (e.g., animals) that don’t experience locomotor-related pains, dysfunctions, or limitations, for example, will have an evolutionary edge on organisms that aren’t optimally mobile, as they’re able to move more effectively, most likely using less energy.
Why is this important to recognize?
It’s very important to recognize that natural selection, by favoring genes that are beneficial in the context of survival and reproduction, acts as a health-shaping instrument, as it has profound implications for our understanding of health and disease. The fact that it pays, in a Darwinian sense, to be smooth and healthy implies that health, not disease, is the expected result of selection, at least under natural conditions. This postulation stands up to scientific scrutiny, in the sense that a number of studies – many of which I’ve talked about here on the site – have found that organisms that live in a natural environment that has remained fairly stable for a long period of time tend to be lean, free of chronic illness, and physically robust.
With that being said, it’s important to remember that all organisms take part in a never-ending arms race and battle for existence and are at the mercy of Mother Nature. Furthermore, one shouldn’t forget that in evolutionary regards health is only important insofar as it affects organismal survival and reproduction and that our resistance to illness and decay naturally declines as we age. If a gene or trait is beneficial in terms of survival and reproduction early in life, it’ll likely become more common over time even if it adversely affects one’s vitality or resistance to disease later in life.
From the perspective of optimizing energy/nutrient conservation and efficiency, it’s beneficial to be able-bodied and possess an immune system that is capable of effectively and rapidly dealing with the challenges that one is likely to encounter. Hence, one would generally expect biological complexes that operate in a “smooth” manner to be favored by natural selection over systems that don’t function as well under the relevant conditions of existence. These evolutionary insights shed light on the origins and etiology of health and disease and what’s required to produce robust, vigorous organisms.