Big Idea V: Evolution happened and continues to happen.

Studying the fossil record is the easiest way to observe that evolution happened in the past. Evolution is still occurring today, but it is more difficult to observe. The minor changes from generation to generation can take thousands or millions of years to accumulate before they are noticeable or result in a distinctly new species. Organisms with very short generation times, however, can provide evidence that evolution is still occurring today. The Fruit Fly, Drosophila melanogaster, is one of the most commonly used model organisms in biology because it is easy to care for, breeds quickly, lays many eggs, and has a generation time of only 10 days. Its genes are easily manipulated through embryological techniques; it is a perfect organism for studying “artificial selection” (human-induced natural selection, used widely in animal husbandry). As a second example from human medicine, the common flu virus changes (evolves) enough every year that a new flu vaccine must be produced to protect us from repeat infection. In addition, the emergence of antibiotic-resistant bacteria is evidence that bacteria have evolved to survive the human-devised drugs that previously would have killed them.

For more discussion on this topic, see the section Evolution in Everyday Life.