Darwin saw evidence that the process of natural selection had occurred in nature, but he was unable to watch it happen. Scientists today, however, can actually observe the evolutionary process in action. Using organisms that reproduce rapidly and can be kept in laboratories in large numbers (such as fruit flies and bacteria), and employing modern tools and techniques (such as DNA sequencing), evolutionary biologists can conduct actual evolution experiments and watch the results.
Scientists don't pick fruit flies because anything about that species is special; they pick fruit flies for expediency. Experiments conducted with fruit flies go a lot faster than experiments with other organisms (such as dogs or sea turtles) because the generation time of the flies is much, much shorter. A fruit fly is born, reproduces, and dies within a couple of weeks. This short life span gives scientists more opportunity to examine changes in heritable traits.
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