Chapter 5, Section 1 Darwin’s Voyage Wednesday, January 6, 2010 Pages 146 -- 156

Objectives State how Darwin explained variations among similar species. Explain how natural selection leads to evolution, and explain the role of genes in evolution. Describe how new species form.

Vocabulary Words Species Adaptation Evolution Scientific theory Natural selection Variation

Who is Charles Darwin? He was a scientist who came up with the idea of evolution by natural selection. Ideas began when we worked as a young naturalist aboard a British naval ship. His travels brought him to the Galapagos Island.

Darwin’s Observations The voyages brought Darwin to many interesting places such as Argentina and the Galapagos Islands. Darwin was amazed at the diversity of living things he saw. Today, there are over 1.7 million species of organisms on Earth. A species is a group of similar organisms that can mate with each other and produce fertile offsprings.

Similarities and Differences While on the Galapagos Island, Darwin noticed that many of the plants and animals were the same as those organisms found on the mainland. Even though many of the plants and animals, there were slight differences. Small vs. large claws. Shape of the shells on the tortoises

Adaptation An adaptation is the ability of an organism to take on a trait that will help it survive and reproduce. Example: The size of a bird’s beak.

Evolution Evolution is the gradual change in a species over time. Darwin thought that species gradually changed over many generations and became better adapted to the new condition. Darwin’s ideas are often referred to as the theory of evolution. A scientific theory is a well-tested concept that explains a wide range of observations.

Natural Selection Darwin published a book called The Origin of Species in 1858. This book proposed an explanation for how evolution occurs. Darwin explained that evolution occurs by means of natural selection.

Natural Selection -- cont’d Natural selection is a process by which individuals are better adapted to their environment and these individuals are more likely to survive and reproduce than other members of the same species. Factors that affect the process of natural selection are: Overproduction, competition, and variations. Over time, natural selection can lead to evolution. Helpful variations gradually accumulate in a species, while unfavorable ones disappear.

Role of Genes in Evolution Without variations, all the members of a species would have the same traits. Evolution by natural selection would not occur because all individuals would have the same chance of survival. Variations come from mutations in genes.

How do New Species Form? New species may come about from separation from the rest of its species. Once a group is isolated, members of the isolated group can no longer mate with members of that species. These separated members might be away for so long that different traits evolve.

Continental Drift Continental drift affected the evolution of species. Evident when examining the fossils from various continents. The split of Pangaea accounts for species being separated from one another and caused them to evolve independently.

Homework Workbook 5.1 (1/8) Worksheet 5.1 (1/7) Vocabulary quiz 5.1 (1/8)