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Darwin’s Theory
Darwin’s Observations
• Background Info: Charles Darwin
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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
o Diversity of living things
o The remains of ancient organisms
o 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 America
o 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
organisms
o Dome-shaped tortoise shells
o 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
beaks
o Finches that ate insects: narrow,
needle-like beaks
o Finches that ate seeds: strong,
wide beaks
• Adaptation
o 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
o He hypothesized the species gradually changed over time
o Organisms became better adapted to the new conditions
• Evolution
o The gradual change in a species over time
• Scientific Theory
o 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
o 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 Selection
o 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
o Overproduction
o Competition
o Variations
Overproduction
• Effect cause by species producing
more offspring than can survive
o Example
• Insects
Variations
• Differences between individuals of
the same species
o Example
• Different foods eaten by the same species of
insects
Competition
• Effect caused by limited food and
other resources
o 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 on
o Scientists later learned, variations can result from mutation and the
shuffling of alleles during meiosis
• Genes are passed from parents to offspring
o Only traits inherited, or controlled by genes can be acted upon by
natural selection