14.4 Disease

Biological bodies are generally evolved to maintain an equilibrium of systems – homeostasis. This includes balancing our nervous system to be alert but not always “on,” as well as making sure our hormones, growth, and metabolism remain functional and working properly. Relatedly, the immune system seeks to fight off pathogens as quickly as possible, prioritizing long-term health over short-term discomfort. And this all occurs within complex systems that could take an entire book to even begin understanding – especially given how many of these systems influence the functioning of others.

All that said, understanding the presence of disease in human evolution and behavior is helpful when considering our modern behavior. In his book, Why Zebras Don’t Get Ulcers, primatologist and evolutionary biologist Robert Sapolsky discusses the evolution of stress responses and how unresolved stress can lead to physiological dysfunction – disease. One of the key points is the myriad ways that chronic stress impacts immune system functioning by flooding the body with hormones that keep the fight or flight response on a constant simmer. Something evolutionary psychiatrist Randolph Nesse calls the Smoke Detector Principle.

In the short video below, edited from a longer lecture, Robert Sapolsky explains how chronic, psychological stress is connected to obesity, hypertension, stroke, cardiovascular disease, and so much more. He ends with the most important takeaway a modern human can have about daily life and health – keep things in perspective and remember the value of social connections.

Not All Diseases Relate to Stress

It is true, there are plenty of diseases that are related to other life factors. They may be connected to unchecked habits (smoking or drinking) or the result of environmental factors beyond our control (pathogens or food safety at a restaurant). Some diseases are even the result of cellular division itself.

Cancer

As cells go throw mitosis, there are multiple opportunities for tumors to develop – and grow. The most common are mutations and an error in apoptosis. Mutations are the result of copying and/or encoding errors that occur during cell division, and can lead to incorrect “programming” as the cells grow and continue to divide. This can lead to the development of a tumor. Mutations can also be the result of environmental carcinogens or simply an error inherited from our parents during conception.

Once a tumor begins to grow, an error in apoptosis can occur. Because of the processes of senescence, all cells should experience apoptosis. It is the loss of apoptosis in tumors that allows these cancerous cells to grow unchecked. Yet, the rate of growth, success of treatment, and other factors in cancer survival often relies upon human behavioral change. This may be due to changes in diet and exercise, the reduction or complete discontinuation of habits like drinking alcohol or smoking/vaping. Treatment success often relies on early detection, which is most common in people who are aware of family histories and genetic tendencies.

Explore “About Cancer” by the National Cancer Institute to learn more about the role of genetics, environmental risk factors, screening and prevention, and more.

Pandemics and Other Pathogens

The SARS-CoV2, or COVID-19, pandemic exemplifies how disease can emerge outside our immediate control. Yet, the beginnings of nearly every pandemic Homo sapiens has faced can be traced back to human behavior. Whether ingesting parasites or bacteria from unsafe foods or swimming in waters rife with algae blooms, human behavior brings us into contact with numerous pathogens during our lifetime.

Anthropologist Katherine Latham links the emergence of major epidemics to the Neolithic Revolution. As humans began to settle into agricultural societies, increased proximity combined with poor attention to hygiene. The result was an increase in infectious diseases. Likewise, living in closer contact to livestock allowed for zoonotic diseases to rapidly evolve and easily pass through wildlife, livestock, and humans. Further, tilling of previously undisturbed soils uncovered bacteria such as anthrax. Novel to the human immune system, it took generations for people to combat these diseases and accumulate appropriate immune responses. Worse yet, poor oral health, nutritional deficiencies, and increased physical stress from the work of farming exacerbated the impact of this transition.

Despite these changes, humans thrived. There are key evolutionary reasons that may explain how this is so.