Evolutionary medicine

Evolutionary medicine or Darwinian medicine is a way to think about how and why evolution changed our bodies over time to make us sick or healthy. People use Darwinian medicine to study biomolecules. They think about how these small molecules in our bodies work together through something called physiological mechanisms. Physiological mechanisms are things our bodies do that make us feel either sick or healthy. People who study Darwinian medicine use these ideas to think about how those mechanisms have changed over time. Understanding these changes can be important to know why some people are more likely to be sick than others.
Core principles.
Experts who practice Darwinian medicine use 5 main ideas when thinking about people’s health. These main ideas help experts to decide what things might affect a person’s ability to be sick or healthy. Below is a list of these ideas and their meanings for Darwinian medicine. 
Human adaptation.
There are some adaptations that have changed our traits over time. Some of these adaptations have made people more healthy. But there are constraints that keep some traits from changing. The presence of constraints means that adaptations that could make people more likely to be healthy are not able to happen. Also, sometimes adaptations can happen but with trade-offs. This could mean changes in one trait that make people healthy might lead to changes in other traits that make people sick.
Disease of civilizations.
A long time ago, we think humans used to hunt and gather food and stay in small tribes. The way humans have evolved supports this. There are communities today that still live a hunter-gatherer lifestyle, but there are also many people who have a very different way of living than how our ancestors did. Evolution takes a long time to happen, and evolution has not caught up with how many people are living today. Because of this, some experts in Darwinian medicine believe that people who do not practice a hunter-gatherer lifestyle are more likely to have problems being healthy. This idea of our evolution not matching the way many humans live today and causing health problems is called “diseases of civilization” or “diseases of affluence”. 
Diet.
Many people eat types of food that are much different than what we ate a long time ago. A long time ago we ate things that grew from the ground and animals from the land or sea. Today there are more options to eat. Some options we have are foods that are made in factories, which have a lot of sugar, salt, and fat. These sugars, salts, and fats, coming from factory foods are not good for people to eat, and can lead to sickness. Some examples of sickness that can come from food are dental caries, obesity, and diabetes. 
Life expectancy.
How long we live is changed by how we live today. There are a lot of sicknesses that are more common now than they were a long time ago. Some of these include cardiovascular disease, cancer, arthritis, cataracts, hypertension, and Alzheimer’s disease. All of these sicknesses are more likely to happen the older you are.
Exercise.
A long time ago, more people used to exercise than people do now. Back then, when people didn’t exercise, it was usually because they were sick or hurt. When a person would rest, it would change mechanisms in the body, and would lead to inflammation. Some people believe that people who don’t exercise have more inflammation in their bodies. This can cause more sicknesses. 
Cleanliness.
People a long time ago were less clean than humans are now. Being clean has helped people be more healthy, but there are trade-offs to being clean. There are some microorganisms that are important for humans to have so that we can have strong immune systems. Some microorganisms that grow strong immune systems can come from dirt and animals. Without these microorganisms, people can have weak immune systems. This means they could be more likely to get sick. 
History.
Darwinian medicine comes from ideas that came from Charles Darwin. Although Charles Darwin had many ideas, the most important pieces that helped form Darwinian medicine came from his work on germ theory of disease. A lot of biologists learned of his ideas and quickly saw how germ theory of disease could help people think about how pathogens evolve, and how people evolve to protect themselves from these pathogens. 
Some papers that have been written and have helped grow the field of Darwinian medicine include a paper by Paul Ewald in 1980, “Evolutionary Biology and the Treatment of Signs and Symptoms of Infectious Disease”. Another paper written by Williams and Nesse in 1991, “The Dawn of Darwinian Medicine” was also important to the growth of the field. These papers made people think more about Darwinian medicine. A book called “Why We Get Sick” was written, and later an online journal was made in 2008 called “Evolution and Medicine Review.