Biological evolution is the process through which living organisms change over time. This change occurs through variations in traits, which can be passed down from one generation to the next. For example, Darwin's theory of natural selection explains how certain traits become more common in a population because they help organisms survive and reproduce better in their environment. As environments change, species may adapt, evolve into new species, or even face extinction. This ongoing process has led to the incredible diversity of life we see today, from tiny bacteria to large whales. Understanding evolution helps us appreciate the connections between all living things.