Speciation is a lineage-splitting event that produces two or more separate species. When we say lineage-splitting it could be geographic isolation, reproductive isolation, or a reduction in gene flow. The classic example of speciation is the Galápagos finch; many species of finches that evolved from a common ancestor. Today, different species of these birds live on different islands in the Galápagos archipelago, isolated from one another by the ocean. In the initial populations of finches, variation existed. Some beaks were better suited for eating foods in specific environments. Since each island had unique resources, over time, birds with beaks suited to those resources survived. Some finches had large, blunt beaks that could crack the hard shells of nuts and seeds. Other finches had long, thin beaks that cold probe into cactus flowers. Still other finches had medium-size beaks that caught insects. Different beaks types became predominant on different islands. Because they are isolated, the birds did not have the opportunity to interbreed and eventually developed into unique species with unique characteristics. This is called allopatric speciation. Allopatric speciation occurs when a species separates into two separate groups which are isolated from one another. A physical barrier, such as a mountain range or a waterway, makes it impossible for them to interbreed. Each species develops differently based on the demands of their unique habitat or the genetic characteristics of the group that are passed on to offspring.

The diagram above documents a famous experiment by Diane Dodd. Dodd took an initial population of Drosophila fruit flies, same species, and separated them into two different containers. The first group was fed food containing mostly starch. The second group was fed food containing mostly maltose. After eight generations apart when the flies were re-introduced, they would no longer interbreed. They bred only with flies of like eating habits and they had become two different species. Speciation resulted in biodiversity!

Use the text to choose all of the correct statements about speciation?

A. In the case of the Galapagos finches, biodiversity occurred because different species flew to different islands.

B. Allopatric speciation results when a geographic barrier separates members of a population.

C. Diana Dodd imposed a geographic barrier on fruit flies.

D. One premise behind speciation is that in any population, variation exists.

E. During allopatric speciation, members of a population change in order to survive in their habitat.

F. During the formation of the Grand Canyon, a population of squirrels were separated. We would expect today, that there are two species of squirrels in the Grand Canyon.

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