How Illness Has Extended the Human Lifespan
The average lifespan of the Peking Man (“Beijing apeman”) of Zhoukoudian was only about 15 years. After more than 500,000 years of evolution, the human life expectancy has now reached the seventies or eighties. In some long-lived countries and regions it is even higher; for example, in China's Hong Kong region the life expectancy is 82.0 years for men and 87.8 years for women.
Illness has contributed enormously to extending human lifespan; it is precisely various infectious and chronic diseases that have improved the human body's ability to adapt to the environment. From the perspective of evolutionary medicine, in the absence of natural enemies, a person's anti-aging capacity keeps evolving and life expectancy keeps lengthening. Without natural enemies, humans have more time and opportunity to discover ways to extend their own lives. People come to understand their own physiology ever better, their ability to adapt to nature and disease improves, their immune systems grow ever more developed, and their lifespan naturally keeps increasing.
Illness is both a bad thing and a good thing. The common cold, for instance, helps train our immune system. If a child grew up from birth in a completely sterile environment, spared infection by all manner of germs, its immune system would never be trained to be strong. Once some new germ appeared among the population, such children would lack the ability to resist it. Children in developing countries such as Indonesia grow up from infancy in unhygienic surroundings, yet their resistance to germs is stronger than that of children in developed countries.
In the book Missing Microbes: How the Overuse of Antibiotics Is Fueling Our Modern Plagues, the author Martin J. Blaser—a leading authority in American microbiology and an advisor to the U.S. president—points out that the “primitive people” living in the Amazon rainforest carry a great many microbes absent from modern humans, microbes that helped our ancestors resist many diseases. Even the notorious Helicobacter pylori is not without its uses; although H. pylori is a precancerous lesion of gastric cancer, it also lowers the incidence of asthma and esophageal cancer.
Thus the microbes invisible to our naked eye—even pathogenic microbes—are helpful to the human body. Without the presence of these germs, our intelligence might still be at the level of chimpanzees, and our life expectancy little different from that of chimpanzees, since we and chimpanzees are closely related species.
Similarly, various chronic diseases also train our bodies, raise our intellectual level, and let us discover which weak points our bodies harbor.
From the moment a person becomes a fertilized egg, he or she is constantly adapting to the environment. Even in the womb, the human brain responds to changes in the environment. For example, if a pregnant woman experiences hunger during pregnancy, the fetal brain reacts to that hunger; when such a fetus grows up, it will prefer high-fat foods more strongly and be more prone to obesity. Because in the early stage of its brain development it already experienced what hunger feels like, its brain retains a deep memory of hunger, which makes it unconsciously store more calories for the body. Likewise, if a pregnant woman is under stress during pregnancy, the fetal brain also responds to the mother's emotions; such a child may grow up to be more anxious, or perhaps deeply depressed, again because they were forced to adapt to the environment while still in the womb. Anxiety and depression are themselves effective ways of adapting to the environment; these things we regard as negative emotions can, under stress, raise a person's chance of survival.
The great infectious diseases of history ultimately leave their mark on the human genome. For example, people who survived malaria carry genes that cause thalassemia or sickle cell anemia; people who survived the plague carry genes that cause hemochromatosis and other diseases. Why would humans carry a disease-causing gene? Because under special circumstances these pathogenic genes enable people to survive harsh conditions. In patients with anemia and hemochromatosis, iron in the body does not readily bind to germs; plague bacilli and other germs run rampant in the human body only with the help of iron, so during plague and malaria epidemics, anemic and hemochromatosis patients had a greater chance of survival.
Many genes in the human genome evolved through the struggle against disease; in this process of evolution, humans' ability to adapt to the environment improved and their life expectancy lengthened. Hemochromatosis and thalassemia were not problems that troubled humans in the past, because back then life expectancy was low and most people did not live to the age at which these diseases manifest. But as human longevity increased, the problems caused by these genes began to surface. Yet as humans continued to evolve, we invented medical technologies to deal with such diseases; phlebotomy can solve the problem for hemochromatosis patients, so these genetic defects have become less lethal in the course of human evolution.
In the course of human evolution, wisdom has grown ever more important to extending human lifespan. Because we are gradually coming to understand the elements in the human genome that affect our longevity, and we keep inventing new technologies to overcome these deficiencies and extend our lives.
For example, as humans come to know more and more about the unknown world, people are also gradually overcoming their own adverse emotions—those feelings of fear, anxiety and depression formed in the womb. In an environment with natural enemies and uncertainty, such people could live longer because of their strong emergency-response ability; but under stable living conditions, these emotions, like hemochromatosis, cause a certain kind of harm to the body. Chronic mental tension may lead them to develop diseases such as cancer. As human wisdom advances and science and technology improve, such people, aided by medication and knowledge, can gradually reduce or even eliminate the influence of these adverse emotions.
Each of our genomes is unique, which is why DNA identification can accurately distinguish each individual from the other seven billion-plus people in the world. This also means that the genetic information each of us carries is not identical; our bodies have unique features, and each of us's life experiences differ. In the end, if an individual wishes to survive better and live longer, the way is not to copy someone else's way of preserving health, but to discover the characteristics of one's own body and use wisdom to adjust oneself so as to adapt better to the environment. Only those who adapt to the environment can survive.
For example, a person allergic to wheat should avoid all wheat-containing foods, rather than obsessively trying to solve the problem of their wheat allergy—a problem most likely caused by genes and possibly fundamentally unsolvable; trying to cure oneself so as not to be allergic to wheat is a waste of effort. People who cannot drink milk lack lactase; what they should do is not learn to drink milk like others, but avoid milk as much as possible and obtain nutrition from other foods. Whether the body has lactase is also determined by the genome, not something medicine can solve. Similarly, people who cannot eat chili peppers should avoid chili; if you cannot eat chili yet insist on eating it, you are fighting against yourself.
We should know our own bodies—which is not hard to do, if only we carefully observe and record how our bodies react to various foods and environments. In life, we should steer clear of our own minefields as much as possible; do not stubbornly regard certain individual traits of one's body as “diseases,” insisting on grinding out the pathogenic mechanism and curing it—many people have worn themselves to death in exactly this way.
Some people have emotional problems and readily attribute them to external stimulation. I suggest such people read We Are Our Brains, a popular-science book on brain science by the world's foremost brain scientist, Professor Dick Swaab of the Netherlands, to understand the true sources of depression, schizophrenia, anxiety disorders and aggressive behavior. Most people's emotional problems are caused by environmental stimulation in the womb; problems with our brains are greatly related to damage done early in life by alcohol, nicotine, toxins in the natural environment and food, as well as by parental illness and drugs taken during pregnancy. To overcome the long-term effects of these injuries, we must, like allergy sufferers avoiding allergens, steer clear of the external stimuli that tend to worsen our mood.
Only when we fully understand our own bodies, our own brains, and the natural world, can our ability to adapt to life and the environment improve. Given that our genes cannot be changed, improving adaptability is the key that determines our lifespan.