Darwin’s Voyage Darwin’s Voyage Darwin’s Observations • As Darwin traveled around the world on a British naval ship, he was amazed by the incredible diversity of the organisms or species that he saw. • Species – A group of similar organisms that can mate with each other and produce fertile offspring. Galapagos Island & South America • Darwin was surprised that many of the plants and animals were similar to organisms on mainland South America, yet there were also important differences. • Darwin inferred that a small number of different species had come to the island from the mainland and that eventually their offspring became different from the mainland relatives. • Adaptation – A trait that helps an organism survive and reproduce. – Ex. Beak shape and size differences in the finches Darwin’s Finches Evolution • Evolution – The gradual change in species over many generations in order to become better adapted to the environmental conditions. – Darwin proposed that evolution occurs by natural selection. • Natural Selection – Process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Factors Affecting Natural Selection • Overpopulation – Most species produce far more individuals than can possibly survive. • Competition – Offspring must compete for food and other resources to survive. • Variations – Difference between individuals of the same species. • Selection – Some variations make certain individuals better adapted to their environment. – These will survive and reproduce, thus possibly passing this allele onto their offspring. Types of Selection • Stabilizing Selection – Natural selection favors average individuals. – Reduces variation in a population. • Directional Selection – Natural selection favors one of the extreme variations of a trait. – Leads to rapid evolution of a population. • Disruptive Selection – Favors both extreme variations of trait – Results eventually in no intermediate forms of the trait and leads to the evolution of two new species. Relating Natural Selection to Evolution • Over a long period of time, natural selection can lead to evolution. • Helpful variations gradually accumulate in a species, while unfavorable ones disappear. • Ex. Faster turtles will be able to escape predators and thus might pass this trait onto their offspring. This species might then be marked by the “fast-swimmer” trait. Role of Genes in Evolution • NOTE: Only traits that are inherited, or controlled by genes, can be acted upon by natural selection. • Ex. Color in moths during the Industrial Revolution How Do New Species Form? • Geographic Isolation – New species can form when a group of individuals remains separated from the rest of its species long enough to evolve different traits. – Ex. Kaibab vs. Abert’s Squirrel • Continental Drift Theory – Emphasizes that Pangea breaking apart resulted in geographic isolation which led to evolution of various species Development of New Species Patterns of Evolution • Divergent Evolution – Pattern of evolution in which species that once were similar to an ancestral species diverge, or become increasingly different – Caused by populations adapting to different environmental conditions and eventually resulting in new species • Convergent Evolution – Pattern of evolution in which unrelated species evolve similar traits because they occupy similar environments in different parts of the world. The Flip Side of the Coin • Mutations or changes in the DNA are rarely helpful but are usually neutral, harmful, or fatal. Summary Questions • What is evolution? What did Darwin observe on the Galapagos Islands that he thought was the result of evolution? • Explain why variations are needed for natural selection to occur. • Describe how geographic isolation can result in the formation of a new species. • Some insects look just like sticks. How could this be an advantage to the insects? How could this trait have evolved through natural selection?