I can… explain how natural selection leads to evolution. You need: A new packet A note guide Warm...
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Transcript of I can… explain how natural selection leads to evolution. You need: A new packet A note guide Warm...
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