Genes, Environment, and Habits Jointly Determine Our Health

Genes are the smallest known units of living things. Modern biology has confirmed that fatalism is, to some extent, reasonable: our life begins as a fertilized egg, and our genome is already fixed when we are but a single cell.

Genes influence our intelligence, health, appearance, skin color, and more. Over our long lives, the genes we inherit from our parents play an important role.

For example, women born into families with BRCA1 and BRCA2 mutations have a higher lifetime risk of malignant tumors such as breast and ovarian cancer. Women from HNPCC (hereditary nonpolyposis colorectal cancer) families are prone to both colorectal carcinoma and uterine cancer (lifetime incidence as high as 30%-60%), and some develop both cancers simultaneously.

Cutting-edge research shows the human genome contains about 20,000 to 25,000 genes. As we have reproduced on Earth, our genome has kept changing; humans accumulate roughly 100 gene mutations each generation. The vast majority are neither beneficial nor harmful, but mutations at certain specific sites can be fatal. Genes are the code of life, recording the challenges we have faced while reproducing on Earth; decoding this code is therefore also decoding human history.

Biological gene mutation is related to many factors.

The environment we live in—the sun, air, water, and food—can cause our genes to mutate. For instance, when the ozone layer is damaged, UVB and UVC bands of solar ultraviolet radiation penetrate directly, damaging our skin, mutating certain genes, and eventually turning malignant into skin cancer and malignant melanoma. So the TCM idea that humans and the environment form an organic whole is scientifically grounded. Mendel's famous pea-hybridization experiments proved that environment is an important cause of gene mutation.

The infectious diseases we encounter (all caused by transmission of pathogenic microorganisms such as viruses and bacteria) also alter our genes. After we survive a serious infection, our immune system records certain molecular fragments of those viruses or bacteria; when the same pathogen strikes again, our immune system can handle it. These fragments are antibodies our immune system uses against certain infections, and they have become part of our genome. By incomplete estimates, about 40% of human genes are related to pathogens. Of the hundred-plus gene mutations we accumulate each generation, roughly half are caused by infectious disease.

Infection with some viruses leaves only scars after recovery, such as smallpox. But infection with other viruses or bacteria can lead to cancer: hepatitis B and C viruses cause liver cancer; HPV (human papillomavirus) causes cervical or anal cancer; EBV can cause childhood lymphoma and nasopharyngeal carcinoma; Helicobacter pylori causes gastric cancer. Whether each newly emerging virus or bacterium will have profound long-term effects on the human body requires long observation and research. A serious scientist will not rashly declare, when a pathogen first appears, whether it will have lasting effects on human health.

Genetic variation is not entirely bad. Differences in skin color, the height and shape of nasal bridges, and stature among humans all result from gene variation. Sometimes genes vary in order to adapt to the environment and help us survive better in nature. The rich diversity of species on Earth also benefits from the various mutations genes undergo under environmental influence. Birds that look wildly different may share a common ancestor; flowers of different colors and shapes may be plants of the same origin; viruses also produce variants as they spread.

As living organisms, genetic variation is normal for us; without it is impossible. Human wisdom advances precisely through genetic variation. Our immune system is continually patching us up, making us better at resisting disease and surviving—though in the process many of our weaker brethren are ruthlessly eliminated. Sometimes a pathogen is so lethal that it causes catastrophe in a single generation, such as the Black Death.

Theoretically, the more strongly we interact with the ecological environment, the faster our genes mutate. Thus as Earth's population density rises and climate and environmental change become more pronounced, the probability of infectious epidemics and new noncommunicable epidemics among humans also rises. From 2009 to 2019 there were five major epidemics (including COVID-19); unfortunately we predicted none of them. Perhaps the next pandemic is already brewing, though we have not yet realized it. Meanwhile chronic noncommunicable diseases closely tied to environment and modern lifestyle—tumors and diabetes, for example—are also exploding. Because food is abundant and meat intake is high, modern people are often obese. Obese people have more estrogen in fat tissue, and estrogen unopposed by progesterone causes all kinds of intractable diseases, including malignant tumors.

Similarly, changes in human social structure and culture give rise to new epidemics. As old villages and small-town communities vanish, the kinship-based communal life of the past breaks down. People live in ever-larger metropolises while new systems of spiritual support have not yet formed, producing an "island effect"; mental illness is thus becoming the next major epidemic. The WHO predicts that by 2030 depression will rank first in the global burden of disease.

So if we want to live healthily, we must learn a great deal and change our bad habits—promiscuity, eating wild animals, drinking, smoking, binge eating, and excessive obesity all make us ill. Genes only partly determine our health and fate; the other part is of our own making.