Evolution: the process by which living organisms change over time due to DNA mutations and adaptation to the environment

Have you ever looked at all the different plants and animals that call this planet home, and asked, “How did this happen?” Do you ever think, “How can a Chihuahua and a Great Dane both be dogs?” Have you ever wondered how flowers became reliant on bees to pollinate them? Why do fish have gills and you have lungs?

You’re not the first person to ask these questions. In fact, one of the biggest questions humans have asked is this: “How do different plants and animals come to be so different from one another, and why do they seem so well-suited to the places they live?” Today, we know a lot of the answers to these questions, but not all of them. We know that all the living things we see around us came to be the way they are through a process called evolution. But just 150 years ago, in the 1800s, this process wasn’t understood at all. It took the work of scientists like Charles Darwin to help us develop our understanding of how evolution works.

How does evolution work?

Evolution is the process by which species change over time through small, gradual changes that add up across generations. These gradual changes are called adaptations, and they help an organism survive and reproduce in a changing environment.

How do these adaptations happen? They happen through small changes within our genes. Our genes are constantly making copies of themselves as we grow and heal. Sometimes, these copies aren’t quite perfect. These slight imperfections are called mutations. Most mutations are harmless and go unnoticed. But every once in a while, mutations are helpful, passing new traits to an organism’s offspring that make it more likely to survive, reproduce, and pass the beneficial gene to later generations.

So, mutations can lead to adaptations that help an individual survive. But how do they lead to more widespread changes across a whole species? The answer is simple: Individuals with beneficial mutations are more likely to survive and they are more likely to have offspring. As a result, across generations, the mutated genes become more common in a population. This is a process called natural selection. This term means that individuals with traits that help them survive are more likely to survive and have offspring who inherit these helpful traits. Gradually, over a very long time, natural selection can change a species so much that a whole new species emerges.

What Charles Darwin learned

The description of evolution that you just read is how we understand it today. Our understanding developed over hundreds of years and thanks to the work of lots of scientists. The most important moments in its development happened in the middle of the nineteenth century (1800s).

A lot of factors helped push scientists to think about evolution in this period. Researchers were uncovering lots of new fossils that proved new species could appear and then disappear over time. New tools, such as microscopes, made it possible to look more closely at cells. The study of animals and plants was beginning to show that some species were related to each other and may have had common ancestors.

One scholar, Charles Darwin, played a key role in turning all this new information into an understanding of evolution. As a child growing up in England, Darwin was very interested in the natural world. He spent a lot of his time collecting specimens of plants and animals and observing their natural habitats. His curiosity about life eventually landed him at the University of Cambridge, where he studied medicine and religion.

In 1831, at the recommendation of his professor, Darwin found himself on a ship called the HMS Beagle, which was sailing around the world to map the coastline of South America. On this voyage, Darwin observed some important things about our natural world.

In South America, Darwin examined fossils of extinct species of animals and compared them to their living counterparts. He saw that extinct species of armadillos and giant sloths looked very similar to living species and he figured out that there was a connection between the past and present organisms. He observed similarities between different species—such as how human hand bones look a little like the bones in a bat’s wing or in a whale’s flipper.

Most important, Darwin studied finches, a type of bird he came across on the Galápagos Islands. He noticed that the shape and size of the finches’ beaks changed from island to island. He concluded that these differences were adaptations to the specific conditions on each island. These observations helped determine how plants and animals have come to be so different from each other and why they are so well-suited to the specific place they live.

What have we learned about evolution since Darwin?

In 1859, Darwin published his claims in a book called On the Origin of Species. At first, his work was fiercely debated, but scientists soon came to accept his main conclusions as accurate. Over the next century, other scientists would build on Darwin’s ideas, improving our understanding of evolution and natural selection.

Natural selection isn’t just something that happened in the distant past. We have seen evidence of it at work around us. For example, in nineteenth-century England, some scientists noticed that the peppered moth was changing color from mostly white to black.

At this time in England, huge factories were being built, and they burned lots of coal to power machines. Smog from coal burning left a dark residue and pollution all over England’s big cities. Scientists today believe that the peppered moths changed colors because they could hide better from predators if they were darker and could blend in with the pollution. Moths with this variation lived longer and the new adaptation was passed down to baby moths.

Natural selection has revealed potential ways that new species are created and how they go extinct. Scientists have learned that humans and all other biological organisms are changed by their physical environments. Using this understanding, researchers have learned all kinds of ways to help our society through advances in medicine, farming, and conserving the natural environment.