Final answer:
According to Charles Darwin's theory of natural selection, giraffes have long necks due to competition for food. Giraffes with longer necks had an advantage as they could reach leaves on tall trees, allowing them to survive and reproduce.
Step-by-step explanation:
Charles Darwin believed that giraffes have long necks because of competition for food. According to Darwin's theory of natural selection, giraffes with slightly longer necks had an advantage as they could reach leaves on tall trees that other giraffes couldn't. These giraffes were more likely to survive, reproduce, and pass on the trait of longer necks to their offspring. Over time, the population contained more long-necked giraffes until eventually, all giraffes had long necks.