I can… explain how natural selection leads to evolution.

You need: A new packetA note guide

Warm Up: What does it mean to have variation?

Wrap Up:• What is an adaptation?

Darwin’s Theory

Chapter 6 Section 1

Darwin’s Observations

• Background Info: Charles Darwino Set sail on the HMS Beagle o 5 year trip around the worldo Naturalist: a person who studies the natural worldo He wanted to learn about the living things he saw on the voyage o He made many stops along the coast of South America then to the

Galapagos islands

His important observations includedo Diversity of living thingso The remains of ancient organismso 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

o A groups of similar organisms that can mate with each other and produce fertile offspring

Fossils• Fossil

o 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 Americao Blown out to sea during a storm?o Set adrift on a fallen log?

Comparisons Among the Galapagos Islands

• Darwin traveled from island to island

• He noticed many differences among the organismso Dome-shaped tortoise shellso Saddle-shaped tortoise

shells

Adaptations• The finches Darwin saw on the

islands were noticeably different

• Most obvious difference was the size and shape of their beakso Finches that ate insects: narrow,

needle-like beakso Finches that ate seeds: strong,

wide beaks

• Adaptationo 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 Americao He hypothesized the species gradually changed over timeo Organisms became better adapted to the new conditions

• Evolutiono The gradual change in a species over time

• Scientific Theoryo 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 mateo 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

o Explanation of how evolution COULD occur in nature

• Natural Selectiono 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 selectiono Overproductiono Competition o Variations

Overproduction• Effect cause by species producing

more offspring than can surviveo Example• Insects

Variations• Differences between individuals of

the same specieso Example• Different foods eaten by the same species of

insects

Competition• Effect caused by limited food and

other resourceso 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

o 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 ono Scientists later learned, variations can result from mutation and the

shuffling of alleles during meiosis

• Genes are passed from parents to offspringo Only traits inherited, or controlled by genes can be acted upon by

natural selection