Humans were not designed for perpetual homeostasis

In the last decade, studies on longevity have multiplied dramatically. Most of them focus on what are commonly called the supporting pillars; diet and exercise, essentially. However, there is a third element that could be considered the third pillar of longevity: the environment.
For several million years, we evolved following a nomadic lifestyle, hunting in small groups and collecting what nature made available. For 99.5% of this time, our adaptive strategy was that of hunter-gatherers, until the invention of agriculture. This means that 99.5% of our genes evolved under those circumstances. Many of the generations that preceded us had to survive in unfavorable environmental conditions. There were predators to outsmart that were more capable and quicker than us, famines to bear, fearsome cataclysms capable of decimating most living species. It was an incessant battle to ensure continuity of the progeny in a hostile and changing environment. Clearly, many of our ancestors didn’t survive such adverse circumstances. They didn’t have the chance to transfer their genetic characteristics to their offspring.

From this point of view, we can understand natural selection as an evolutionary tool, where only the strongest have the ability to maintain (and to transfer to their offspring) their successful traits. Natural experimentation, through random mutations, has often generated genetic blind alleys. The great variability of our genes has always been the resource through which to cope with new environmental pressures. As a consequence, our nervous system has evolved to keep us as close as possible to a state of homeostasis: that state of comfort in which the environment satisfies every physical requirement.

But what is the state of comfort? How could we define it? More than a real definable sensation, it is the absence of elements that create discomfort. Our species would never have crossed hot deserts and desolate lands with glacial temperatures if there had not been the promise of a physical reward, whether it was a less hostile environment or the availability of more abundant food. To be able to transmit their genetic traits to successive generations, every single species living on this planet has had to demonstrate a high degree of motivation. Motivation is necessary to overcome the numerous challenges presented by the environment. In this regard, one can define comfort and the sensation of pleasure as the two most powerful and immediate rewards that can exist in nature.

Homo sapiens differentiated around 200,000 years ago. Consequently, our genetic characteristics and intellectual capabilities do not differ from the Stone Age man who built stone tools to hunt his prey. Since then, we have had to overcome countless challenges, including escaping from prey and surviving interminable glaciations. Until the very recent past, comfort has never been the norm; rather, there was always a balance between effort and reward. Of course, our ancestors didn’t have even a tiny fraction of our modern advanced technology.
Since the beginning of the last century, technological progress has been so overwhelming that it has interrupted our fundamental biological link with our environment. Artificial lighting, electronic devices, plumbing systems, central heating and air conditioning, cars, and stores give us the ability to fine-tune the characteristics of our artificial environment to our liking. Our control is so complete that many of us live under a state of perpetual homeostasis. The outdoor conditions are irrelevant, whether they are extreme desert heat or glacial cold. Many of us can easily get up long after sunrise, eat a breakfast composed of fruit grown on another part of the planet, go to work in a climate-controlled car, spend the day in a climate-controlled office, and return home without ever having had any real contact with the outdoor environment. Humans are the first species to appear on this planet that can completely ignore the environmental conditions. Without environmental challenges to face or obstacles to overcome, humans of the third millennium are overcharged, overheated, and understimulated. As a consequence, we are overweight, lazy, and have weak immune systems.

Modern humans no longer suffer from diseases of lack; on the contrary, most of our problems are associated with excess. The last century has seen the explosion of conditions like obesity, diabetes, allergies, hypertension, and celiac disease. There are ever more people affected by autoimmune diseases like rheumatoid arthritis and Parkinson’s disease. Our immune systems are literally attacking ourselves. It is as if the lack of stimuli and external threats has provoked a reaction against ourselves (by definition, an autoimmune reaction). Within the scientific community, there is an increasing consensus that being in a perpetual homeostatic state, without environmental alterations, is detrimental to the state of our health. Evolution forged our instincts so that our efforts would be aimed at attaining a state of comfort. Comfort, for most of our evolutionary journey, never represented the norm, but a temporary reward after overcoming significant challenges. Human biology needs stress from the environment, the sort of positive stress that stimulates our physiology, turning on our adaptive responses with a positive effect on the nervous system.

Today, more and more, a certain counterculture is discovering that the environment has the ability to positively stimulate our physiology; it takes only a few weeks to adapt to certain environmental conditions. When we are at high altitudes, the body responds by producing more hemoglobin to ensure sufficient transport of oxygen to the tissues. When the external temperature is high, the body immediately reduces the quantity of minerals lost through sweat and decreases the production of urine, to prevent dehydration. Even sweating, being an exothermic process, is favored by the circulatory system to cool the body when there is excessive heat. On the other hand, no environmental stimulus is able to produce such positive physiological changes as exposure to low temperatures.
The circulatory system is equipped with a huge number of arteries, veins, and capillaries, which carry blood, and consequently oxygen, to the body’s tissues. Arterial blood carries oxygen from the heart and lungs carries oxygen to peripheral tissues, and venous blood which brings carbon dioxide (a byproduct of cellular respiration) to the lungs. This complex and articulated system extends for several tens of kilometers in our body, and is equipped with smooth muscle, which is capable of compressing or dilating these vessels. The vasoconstriction and vasodilation that ensue are necessary to maintain a constant temperature at the level of the vital organs, at the expense of the peripheral regions such as hands and feet. When we expose ourselves to cold, our smooth muscles contract vigorously, retaining blood in the thoracic region and preventing a useless and dangerous heat loss at the peripheral level. This simple ability is indicative of a healthy cardio-circulatory system, but requires stimuli on a regular basis to maintain a certain efficiency. Those who, like the vast majority of people, live under a constant condition of homeostasis do not exercise this fundamental characteristic. Living constantly in a too-narrow temperature range leads to weak cardiovascular smooth muscle. Even people who are fit and apparently in good physical condition potentially hide an inadequately trained cardiovascular muscular system. Globally, cardiovascular diseases contribute to more than 30% of mortality.

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