Humans haven’t mutated this much…yet. Credit: iStock

The word “mutation” may conjure up images of fictional monsters, Marvel X-Men and creatures with non-human characteristics. It’s true that mutations are often associated with disease: something that has gone wrong in the body to produce an oddly shaped body part or sometimes cancer. However, mutations can’t be categorized as “good” or “bad” so easily. In fact, some mutations turn out to be a good thing, such as the human affinity for long distance running. More on that in a bit, but first a lesson in mutations …

A mutation is a permanent alteration in the DNA sequence that makes up a gene. In other words, the DNA—genetic material that contains information about inherited characteristics—changes in a way that makes the gene different than how it normally appears in most people. Because of this change, certain proteins and their functions change, too, leading to what is called “genetic variation.” All of us have a number of harmless mutations that make us unique. These types of mutations are the most common kind of genetic variation in people.

Mutations can be passed down from our parents and ancestors (inherited) or can happen because of environmental exposures after we are born (acquired). Diseases such as muscular dystrophy are an example of inherited mutations. Skin cancer that develops from exposure to ultraviolet radiation from the sun is an example of an acquired mutation. Not all mutations are harmful, however. Those that have occurred as part of evolution may have allowed humans to survive and thrive—and perhaps have helped us become the planet’s leaders in endurance running.

Two to three million years ago, an environmental change that brought people to the open, dry landscapes of sub-Saharan Africa caused a shift in the way we moved. Our ancestors had developed the ability to walk upright and run as means of transportation and exploration. Along with this postural shift came the large aerobic capacity, ability to sweat and large leg muscles that are ideal for distance runners.

Researchers have now identified a single gene that may have also contributed to our rank as among the top endurance runners in the animal kingdom. The mutation seems to have occurred around the same time humans began walking on two feet, meaning it probably played a role in our supreme running capabilities.

Some mutations occur by chance, without explanation. It’s likely, however, that the mutation that led to endurance capacity happened because of changing needs. Chasing prey over long distances allowed early humans to eat a more carnivorous, protein-heavy diet, which furthered evolution and increased survival. This mutation may have been essential for running faster and farther, which led to the endurance trait we see in modern humans today.

It seems we are now reaping the benefits of our mutant ancestors. When we line up for our next road race—or dash across the street for a cup of coffee—we can thank those small, barely noticeable changes in our genetic code.

Brady Holmer is a PhD student in exercise physiology at the University of Florida. His lab focuses on cardiovascular physiology; mainly how exercise can play a role in health, disease and aging.