The average adult spends between 50 and 70 percent of their life sitting, and few spend the rest of that time doing any physical activity. If we were to get into a time machine to observe our ancestors from about ten thousand years ago, we could see that their customs were exactly the opposite. They spent more than 70 percent of their time active.
Many of the characteristics and behaviors that made us more fit in the past now make us maladapted, because the environment in which the human genus emerged has changed so much, and so quickly that it is remarkable that we can continue to live as we do. The irony is that the greatest agent of change in our environment is ourselves.
Let's get back in the time machine and go back 1.5 million years. We are in Africa, in a region of grasslands and isolated patches of trees. It is a tropical region, the climate is warm, and the sun rarely gives us a break by hiding behind a cloud. As good time travelers, we have brought sunscreen, bug spray, a hat, and a camera. Several meters ahead we see a group of Homo erectus, one of the first representatives of the human genus.
He stands upright on two legs and has a brain quite similar to ours in size. The sun bathes his black, sweat-covered skin. He is following the trail of prey. We don't see that they have bows and arrows, or spears, they haven't been invented yet. They do carry some stone tools, but they don't stop for long and get moving again. They run and run, long enough to exhaust their prey. They find it agonizing, the result of overheating of the body.
We, as time travelers, had to move with the vehicle we brought, since we couldn't keep up with Homo erectus. Although the body we have has evolved to do the same thing he was doing, our lifestyle distances us from this ancestor. We couldn't even run for the bus, because we rarely run, and we walk very little. The industrial era has taken us far from the evolutionary path that the human genus has been following since the time of Homo erectus, we have gone from being a highly active animal to being totally sedentary.
Evolutionary Medicine: Bridging the Gap Between Our Past and Present
Our species evolved over 200,000 years ago on the African savanna, a hot, dry environment. We were not designed for office buildings, driving trucks for thousands of miles, or playing soccer and tennis. Our entire anatomy points to a special type of adaptation: that of a highly active animal that can run and run under the relentless tropical sun without overheating or getting sunstroke; that can eat almost anything; and that stores up for times of scarcity. All of this made us extremely flexible in the face of changes in our environment, which is why Homo sapiens was able to colonize almost any part of the globe.
However, for at least the past five thousand years, we have been deviating more and more from this evolutionary path, and the customs of the industrialized world are taking us further away from the conditions for which we are adapted. We incur these kinds of mismatches every day, which in themselves may not be so harmful, but the cumulative effect makes us sick, and in some cases fatally.
Many of the most annoying diseases and ailments of modern society can be prevented simply by becoming more aware of our body's evolutionary history. Understanding how and why each of the evolutionary adaptations that characterize us has arisen, and elucidating how a modern disease disrupts that adaptation, allows us to prevent it. This line of thinking has given rise, in recent decades, to a new way of trying to understand diseases.
One case was that of Paul Ewald, who in 1980 published the scientific article "Evolutionary Biology and the Treatment of Signs and Symptoms of Infectious Disease," in which he disagreed with the idea that genes are the only culprits in susceptibility to certain diseases.
The causes had to be sought in our species' departure from the environment for which evolution has adapted us. Ewald's study was followed by many more, as well as books, and even a specific scientific journal: Evolution and Medicine Review. The goal of evolutionary medicine is to reduce the mismatch between our evolutionary past and our current lifestyle.
Our humanity comes at an evolutionary cost, due to the exceptional combination of things we can do. We have the body plan of a fish, dressed as a mammal, twisted in such a way that we can walk on two legs, talk, think, and have fine control over our fingers. We do not have an intelligent or reasonable design; we are the result of adaptations that have been layered on top of each other.
The culture that our immense brain has developed has changed us too quickly for natural selection to have been able to adapt us, and that is why we suffer from hemorrhoids, varicose veins, back pain, irritable bowel syndrome, hypertension, heart attacks, diabetes, appendicitis, and even cancer. For evolutionary medicine, "adaptation is a more useful concept than normality," wrote evolutionary biologist George Williams.
The Evolutionary Mismatch Behind Our Modern Diet: Why We're Getting Sick
"The disconnect between the human past and present is causing our bodies to fall apart in a predictable way," says paleontologist Neil Shubin in his book Your Inner Fish. Almost every disease and ailment has evolutionary components. The human body has evolved to become a perfectly oiled machine for storing nutrients. Thousands of years ago, this ability saved our ancestors from starvation in times of scarcity. But today, this adaptation that evolution has bequeathed to us is generating humanity's main nutritional problem, which is not hunger, but overweight.
In 1962, anthropologist James Neel suggested that our ancestors adapted to an explosive existence, adapting to periods of abundance with spoils such as a good catch, and to the counterpart of long periods of scarcity. Thus, the body adapted to accumulate nutrients, in case they were scarce at some time of the year. This accumulation is reflected in the fat that is stored in the abdomen in men; and in the hips and thighs in women, who find it very difficult to reduce this fat with exercise, an adaptation to ensure that they never run out of reserves to support their offspring.
Today, we don't have to walk several kilometers a day to get food like our ancestors did; just a few steps to the refrigerator. So, we accumulate more quickly, without burning calories. The plasticity in the choice of these foods is also making us sick, because we have specialized in some marginal parts of this dietary potential that we have. We eat little fiber, for example, which makes us feel less satiated, and in the long run causes us diverticula, and in extreme cases appendicitis.
The intestine is prepared for foods with fiber, which do us good. When we send it junk food, or processed foods, lacking in fiber, it is more difficult for the intestinal walls to mobilize these foods, because being smaller they leave more space. This causes small balloons to appear in the walls of the intestine, which are diverticula, which become inflamed and are painful. Sometimes, due to the effort the intestine has to make, the pressure affects the appendix, which ends up inflamed and infected, and can degenerate into appendicitis.
This type of diet lacking in fiber is also responsible for irritable bowel syndrome. The stress of the modern world exacerbates this condition by further slowing down digestion. All of these ailments can also degenerate into cancers of the intestine or colon.
Salt and Sugar: The Evolutionary Mismatch Behind Modern Health Problems
Among modern-day hunter-gatherer societies, hypertension and heart failure have not been discovered. They eat little salt, few saturated fats, few carbohydrates, and many fibers and vitamins. This is how our ancestors were, and our bodies have evolved for that type of diet. If we contradict it, we get sick.
Since the 1980s, S. Boyd Eaton and his colleagues have extensively researched the nutrition of our Paleolithic ancestors, which is key to the movement that emerged from those times and is now known as the Paleo Diet, a return to the diet for which our bodies have adapted.
Hypertension is associated with a poor diet. Our prehistoric ancestors did not have a salt shaker on the table all the time, they barely ingested the salts that they could find naturally. Excess salt in the body generates an increase in extracellular fluids, which in turn increase blood volume, and end in higher blood pressure. Salt also makes us urinate more and sweat more. The heart ends up failing due to these and other imbalances.
Hypertension subjects the arteries to excessive work that produces small wounds, which, as they heal, harden the arterial walls: atherosclerosis. In the long run, the arteries narrow, with an eventual total cut in blood flow, which if it is the brain that is lacking blood, can produce a stroke.
Just as excess salt is harmful, so is sugar abuse. Millions of people around the world are affected by diabetes, which is the disease resulting from excess glucose in the blood. Sugar molecules cause water to be expelled from cells in an attempt by the body to dilute the blood to normal levels. Excess water is excreted by the kidneys, and glucose goes through the same place, in a body's struggle to get rid of excess sugar.
Type II diabetes is a complicated disease, but from an evolutionary point of view it becomes more understandable, it can lead to blindness, kidney failure and death. Obviously, excess sugar enters our body through one place only: the mouth. We eat it either as sugar or as carbohydrates.
In the past, we did not have sugar at our fingertips, because glucose is not abundant in nature. For that reason, our body is prepared to let all the glucose that enters the body pass through, since the cells use it as energy.
Our ancestors were not that sedentary either, so they used the glucose they ingested as energy or stored it for times of scarcity, but their bodies never saturated. Now we not only ingest too much sugar, but we do little or no exercise.
Back Pain: An Evolutionary Mismatch
This lack of activity also affects one of the most important parts of the body: the spine. Like other ailments, it also has an evolutionary reason. We must not forget that we are primates who have only recently begun to walk on two legs, speaking in evolutionary terms.
Our ancestors began to walk on two legs about 7 million years ago, but the body we have today began to evolve only about 2 million years ago. The lives of these hominids during all those millions of years required constant physical activity, while in recent centuries the daily chores barely require us to move much.
Eight out of ten people have or have had back pain at some point in their lives. The evolutionary past of this problem goes back to the times when that spine went from being curved and horizontal most of the time to being erect and vertical. The vertebrae were stacked on top of each other to balance our immense head on our legs. The spine normally curves in four parts, two forward (in the neck and lower back), and two backward (in the upper back and pelvic region).
Our closest primate relatives, chimpanzees and gorillas, do not have any of these curves. Their spine is a large arch that starts at the base of the skull and ends at the pelvis, like a suspension bridge. Evolution has taken us away from this architecture, giving us ligaments, cartilage, and muscles to be able to curve the vertebrae in this way, which is what keeps us upright and allows us to walk on two legs efficiently.
All of these changes are very recent, and we were still adapting a few thousand years ago, so that our activities change completely and put our entire evolutionary past in check. Although our back is not a finished design of evolution, but rather seems like a living patch, back pain does not exist among hunter-gatherer societies, but only among industrialized ones.
The pain is often so intense and constant because, literally, the vertebrae, the intervertebral space, the ligaments, and muscles related to the spine are plagued with pain sensors. This is because it is a very important part of our anatomy, so we must realize when we are doing something wrong, and pain is the alarm.
Current low physical activity stiffens the ligaments, takes away their flexibility, and tenses the muscles, so any effort we put on the spine, such as lifting a box off the floor, can end in a herniated disc. Overweight also damages it. Even our pillows or soft beds create constant tension on our spines.
Our ancestors slept on their sides on the ground or on some "bed" of leaves, resting their heads on their arms. They did not carry weight in front, but behind or on the head, so as not to strain the back muscles. These are customs that can be seen among modern hunter-gatherers.
But it is not only our backs that are crying out for us to go back to the lifestyle for which we evolved, but the rest of our bodies, as we have seen. This ancestral lifestyle is not incompatible with the current one. We can become more active, eat better, and with that we could avoid the vast majority of the ailments that affect us. Knowing our evolutionary past helps to prevent the most common diseases of mankind.
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