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Darwin’s Theory outline notesPages 138-145

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1. Darwin’s Observations

Darwin’s important observations included the diversity of living things, the remains of ancient organisms, and the characteristics of organisms on the Galapagos Islands.

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A. Diversity

Species: grouping of similar organisms that can mate with each other and produce fertile offspring

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B. Fossils

Fossil: preserved remains or traces of an organism that lived in the past

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2. Galapagos Organisms

In 1835, Darwin reached the Galapagos Islands.

Darwin compared the similarities and differences he saw in the Galapagos Island organisms to those from other parts of the world.

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A. Comparisons to South American Organisms Many organisms from the Galapagos Islands were

similar to those from South America.

There were also many differences between the animals.

Darwin hypothesized that some different plants and animals had come to the Galapagos Islands from the mainland. Eventually the offspring became different from their mainland relatives.

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B. Comparisons Among the Islands

Darwin noticed many difference between the organisms on each of the islands.

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C. Adaptations

Darwin noticed that the finches on the islands were well suited for the food it ate.

Adaptation: a trait that helps an organism survive and reproduce

**Think about the Bird Beak Lab that we did in class. We saw how certain beaks made it easier to pick up and “eat” the seeds.

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3. Evolution

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A. Darwin’s Reasoning

Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions that were different from those on the mainland. Perhaps, Darwin hypothesized, the species gradually changed over many generations and became better adapted to the new conditions.

Evolution: gradual change in a species over time

Scientific theory: well-tested concept that explains a wide range of observations

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B. Selective Breeding

Darwin also studied selective breeding of pigeons. By allowing only pigeons with many tail feathers to mate, breeders produced pigeons with 2-3 times the usual number of feathers.

Darwin thought a process similar to selective breeding might happen in nature.

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4. Natural Selection

Natural Selection: 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

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A. Overproduction

Most species produce more offspring than can survive

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B. Variations

Variation: members of a species differ from one another in many of their traits

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C. Competition

Food and other resources are limited so members of a species must compete with each other to survive

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D. Selection

Some variations make individuals better adapted to their environment.

Darwin proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear.

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E. Environmental Change

A change in the environment can affect an organism’s ability to survive. Environmental change can lead to selection.

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F. Genes and Natural Selection

Variations can occur from mutations. Only traits that are inherited, or controlled by genes, can be acted upon by natural selection.