Darwin’s Theory

Darwin’s Observations Background Info: Charles Darwin Set sail on the HMS Beagle 5 year trip around the world Naturalist: a person who studies the natural world He wanted to learn about the living things he saw on the voyage He made many stops along the coast of South America then to the Galapagos islands His important observations included Diversity of living things The remains of ancient organisms The characteristics of organisms on the Galapagos Islands

Diversity Darwin was amazed by the tremendous diversity of living things Scientists have observed 1.7 million species of organisms on Earth Species A groups of similar organisms that can mate with each other and produce fertile offspring

Fossils Fossil Preserved remains or traces of an organism that lived in the past

Galapagos Organisms Darwin observed the greatest diversity of organisms on the Galapagos Islands Comparisons to South American Organisms Many Galapagos organisms were similar to organisms on mainland South America Darwin hypothesized that the ancestors of Galapagos animals and plants came from mainland South America Blown out to sea during a storm? Set adrift on a fallen log?

Comparisons Among the Galapagos Islands Darwin traveled from island to island He noticed many differences among the organisms Dome-shaped tortoise shells Saddle-shaped tortoise shells

Adaptations Adaptation The finches Darwin saw on the islands were noticeably different Most obvious difference was the size and shape of their beaks Finches that ate insects: narrow, needle-like beaks Finches that ate seeds: strong, wide beaks Adaptation A trait that helps an organism survive and reproduce

Evolution Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions different from mainland South America He hypothesized the species gradually changed over time Organisms became better adapted to the new conditions Evolution The gradual change in a species over time Scientific Theory A well-tested concept that explains a wide range of observations Darwin’s Theory of Evolution

Selective Breeding Breeding animals by only allowing certain animals to mate Example Race horses are selectively bred to obtain the trait of speed Darwin bred pigeons with ONLY large, fan-shaped tail feathers

Natural Selection Book by Charles Darwin, The Origin of Species Explanation of how evolution COULD occur in nature Natural Selection The process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other member of the same species Factors that affect the process of natural selection Overproduction Competition Variations

Overproduction Effect cause by species producing more offspring than can survive Example Insects

Variations Differences between individuals of the same species Example Different foods eaten by the same species of insects

Competition Effect caused by limited food and other resources Example Direct (physical fights) Indirect (not finding enough food to eat)

Environmental Change Environment can affect an organism’s ability to survive This can then lead to selection Monkey Flowers Can’t grow in soil with high concentration of copper

Genes and Natural Selection Darwin could not explain what caused variations or how they were passed on Scientists later learned, variations can result from mutation and the shuffling of alleles during meiosis Genes are passed from parents to offspring Only traits inherited, or controlled by genes can be acted upon by natural selection