Evolution by Natural Selection

What is a species? A group of similar organisms that can mate with each other and produce fertile offspring

What did Darwin notice on the Galapagos Islands? Many of the plants and animals on the Galapagos were similar to organisms on mainland South America However, there were also important differences between the organisms on the islands and those on the mainland Look at figure 2 on page 174

What did Darwin conclude led to the differences between species? After studying the different finches on the Galapagos Islands Darwin concluded that their different beak shape was due to an adaptation Adaptation – A trait that helps an organism survive and reproduce

A. What types of things would bird number 1 eat? C. 3? 4. 4?

Evolution – the gradual change in a species over time What did Darwin start to believe was occurring amongst the different species? Darwin thought the species gradually changed over many generations and became better adapted to the new conditions Evolution – the gradual change in a species over time

Why was Darwin’s idea considered a scientific theory? It was a well-tested concept that explains a wide range of observations

Think Pair Share What did Darwin discover on his voyage to the Galapagos Islands that led to his theory of evolution?

Darwin and Alfred Russell eventually proposed an explanation for how evolution occurs in a book called what? The Origin of Species This book explained that evolution occurs by means of natural selection

What is Natural Selection? The 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

What are the factors that affect the process of natural selection? Overproduction Competition Variations Selection

How does overproduction affect natural selection? So many species are produced that there are not enough resources (food, water, and living space)

How does competition affect natural selection? Since food and other resources are limited, the offspring must compete in order to survive

How do Variations affect natural selection? Any difference between individuals of the same species is called a variation Some variations of a species may provide an advantage over the other members of the species without the variation

Differentiate between adaptation and variation. Think Pair Share Differentiate between adaptation and variation.

How does the environment select which organisms survive? Individuals that are better adapted to their environment are more likely to survive and reproduce passing on the helpful trait to the next generation In effect, The environment “selects” those organisms with helpful traits to be the parents of the next generation

How is natural selection related 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

What role do genes “play” in evolution? Darwin did not know anything about genes or mutations so he could not explain what caused the variations or how they were passed on Only traits that are inherited, or controlled by genes, can be acted upon by natural selection

3 Explain how natural selection leads to evolution. Rate Yourself 4 Apply concepts of natural selection and evolution by creating a scenario that demonstrates the ideas 3 Explain how natural selection leads to evolution. 2 Describe how the evidence supports evolution. 1 Identify evidence for evolution.