Evolution (noun, “EE-vol-oo-shun”, verb “evolve,” “EE-volve”)
In biology, evolution is a process by which species change over time. Evolution is a theory — an explanation about how the world works, backed by evidence. The theory of evolution states that groups of organisms change over time. The theory also explains how groups change. That’s because some individuals in the group survive to reproduce and pass on their genes. Others do not.
Keep in mind that groups don’t evolve to become more “advanced” than their ancestors. Their ancestors did well enough to pass on their genes, after all! But species are always changing. So are their environments. Sometimes their environment might have more or less food. A new predator might appear. The climate might change. Those challenges make it harder or easier for some individuals in a group to survive.
Since every individual within a group is different, some usually have traits that help them survive the change. These individuals will be more likely to survive and reproduce. Over time, the group evolves as more and more individuals with those traits survive.
Scientists have a lot of evidence that evolution occurs. For example, fossils show how apes came to walk upright over millions of years, leading to the evolution of humans. Standing on two legs is a great way to get around. But it has some drawbacks — in the form of sprained ankles and lower back pain. Overall, though, it was beneficial to the species that tried it — which is why we’re standing here today.
There’s also plenty of evidence that evolution is taking place now. For example, bacteria are evolving in ways that help them resist antibiotics. As the climate changes, tawny owl populations are becoming more brown than gray. There is less snow cover that might make a brown owl stand out, and browner owls hide better in brown trees.
Some scientists also use the word evolution to refer to a series of changes in the non-living world. The shape of mountains might evolve as time wears them down and rocks below push them up. A computer chip might evolve as new innovations help it work faster.
In a sentence
In cities, some species of birds have evolved shorter wings, which help them dodge traffic.