Introduction: When populations of the same organism become isolated from each other, they eventually will lose their ability to reproduce together. Over time, because of this isolation, each of these populations will become a new species, well adapted for its particular environment. This is called speciation. 

Speciation often occurs on islands, when populations do not have access to others like them. In the Galapagos Islands, Darwin's finches are a prime example of this. Each species of finch is derived from a common ancestor, but is specifically adapted to the island on which it lives. The beaks of the different species are well-suited for what that bird eats. The thicker beaks are best for breaking apart large seeds and nuts, while the smaller beaks are best at handling small seeds. Other beaks are adapted for eating fruits, while others eat insects. Whatever the beak shape, each bird is a different species that arose from being isolated on a particular island. This idea is the basis of the Theory of Evolution.

There are times when different species are able to reproduce, but quite often their offspring are sterile, unable to reproduce themselves. For example, a mule is the product of a donkey and a horse.

Directions for this Lesson: Answer the practice questions and then watch this video about the different was by which new species can arise.