Give an example of a species and how natural selection affected it over time. Focus on one specific trait of that species.

Natural selection is a concept described by Charles Darwin as a basic and fundamental mechanism of the theory of evolution. The term was introduced in his popular book, "On The Origin of Species," in 1859. Natural selection describes the process by which advantageous traits that allow for better adaptation within an animal population become more common over generations, thus changing the genetic composition of that population. Natural selection is evident in humans as well as many animal species.

Natural selection has been observed on many species, though one of the most prevalent as observed by Charles Darwin was in finches. Scientists found that the birds were all similar to a single type of finch found on mainland South America, suggesting that these mainland finches had originally colonized the islands in the Galapagos. However, these finches were slightly different from the original mainland species as well as from each other. They showed distinct variation in beak size, beak shape, and claw size. The differences were attributed to the differing food sources available on the various islands in the Galapagos. Long, thin beaks were suited for catching and eating insects whereas others had large, strong beaks suitable for cracking nuts open. Drawin concluded that finches evolved overtime through natural selection which determined their adaptations to various food sources. Variations which gave any individual a competitive advantage made them more likely to survive and therefore reproduce, as seen in the finches who survived on a certain food source with their suited beak, and could continue their the passing of their genes through generations.