DNA, the molecule that preserves our genetic material, is formed by a sequence of building blocks called nucleotides. DNA is formed by only four different types of nucleotides, but millions of these combine to form very long sequences called chromosomes. The order of nucleotides within the chromosomes is very important, since it contains the information that encodes genes and other functional elements of our genome. Mutations happen when the sequence of nucleotides is altered. This can be due to several reasons:

First, mutations can happen naturally. During the life of an individual, the DNA needs to be duplicated many times and, sometimes, mistakes occur. Each of our cells has a total of 3 billion nucleotides. Imagine the complexity of accurately copying this amount of information! Luckily, not all of our nucleotides are equally important, so having just a few mutations is often tolerated. However, the more mistakes the DNA in our cells accumulate during life, the more likely it will be that the alteration will affect some important sequence and cause a deadly disease such as cancer. Mutations can also happen in the cells that go on to form sperm and eggs. In these cases, mutations are inherited by babies and can cause fatal congenital disorders such as heart malformations.

Mutations can also be caused by external agents called mutagens. These agents can be chemicals—such as the nicotine in tobacco—or radiation sources—such as the ultraviolet light that makes us tan on a sunny day. These mutagenic agents break the DNA in our chromosomes or make us introduce more mistakes when we duplicate our DNA. Luckily, our cells have mechanisms to repair this damage, but sometimes the harm is so profound that it just can not be fixed. As with natural mutations, these induced mutations can increase our risk to develop diseases.

However, not all mutations are bad. Some mutations can introduce improvements in the functioning of our genes and make us healthier or smarter. Beneficial mutations can also provide us with advantages to adapt to our environment. For example, certain mutations in hemoglobin, the protein that transports oxygen in our red blood cells, allow people to breathe better at high altitudes, where there is less oxygen in the air.

Most mutations, though, have both pros and cons. For example, mutations in hemoglobin can also cause sickle-cell anemia and impede people to breathe properly even where there is lots of oxygen in the air. People with this disease, however, are protected from infectious diseases such as malaria.

Hence, mutations are a natural part of life. They contribute to generate genetic diversity in our DNA and allow us to adapt to new environmental challenges. We need, however, to limit our exposure to mutagenic agents that could overload our genomes with more mutations than the ones we can tolerate.