Today many different species of tortoise may be found in he Galapagos islands. Using your knowledge of evolution, explain how these many specues arose from one common ancestor?

http://en.wikipedia.org/wiki/Gal%C3%A1pagos_tortoise

The multitude of tortoise species found in the Galapagos Islands today is indeed a result of evolution from a common ancestor. To understand how this diversity arose, let's break it down step by step:

1. Common ancestor: It all goes back to a single species of tortoise that first arrived on the Galapagos Islands millions of years ago. This original tortoise population had certain genetic variations and adaptations that allowed them to survive and reproduce in their specific environment.

2. Geographic isolation: The Galapagos Islands are separated from each other, which has led to a phenomenon called geographic isolation. Different islands have unique conditions and resources available. Over time, the tortoise population became isolated on different islands, leading to the formation of distinct populations.

3. Natural selection: Each isolated population was subject to different environmental pressures, such as food availability, climate, and predation. These variations in environmental conditions influenced the survival and reproduction of the tortoises. Through a process known as natural selection, certain traits that were advantageous for survival in a particular environment were favored, while others that were less beneficial were selected against.

4. Adaptive radiation: As the isolated tortoise populations adapted to their specific environments over generations, they underwent a process called adaptive radiation. This process involves the diversification of a common ancestor into multiple species, each with distinct characteristics and traits suited to their specific island habitat. For example, tortoises on islands with abundant vegetation may have evolved longer necks to reach higher food sources, while those in drier environments may have developed traits to conserve water.

5. Genetic divergence: Over time, the accumulation of genetic changes through successive generations resulted in genetic divergence among the isolated populations. This means that the genetic makeup of the tortoises on different islands became distinct from each other. Eventually, these genetic differences became significant enough that the tortoises from separate islands could no longer interbreed and produce viable offspring, classifying them as separate species.

6. Speciation: Through the processes of natural selection, adaptive radiation, and genetic divergence, the original tortoise species diverged into multiple species, each well-adapted to its own unique island environment. This diversification increased the overall biodiversity of tortoises in the Galapagos Islands.

By understanding the principles of evolution and observing these unique circumstances in the Galapagos Islands, scientists can piece together the evolutionary history of species like the tortoises and explain how a single common ancestor gave rise to the incredible diversity we see today.