Download Darwins Theory 7.1 Life Science

DARWIN’S THEORY
Chapter 7 Section 1
Darwin’s Observations
• Darwin’s observations included the diversity of organisms, the
remains of ancient organisms, and the characteristics of
organisms on the Galapagos Islands
• Scientists have identified over 1.7 million species of organisms
on Earth!
• Species: group of similar organisms that can mate with each
other and produce fertile offspring.
Galapagos Organisms
Comparison to South American Organisms:
Iguanas on the mainland had smaller claws but iguanas on the
island has larger claws. Why?
• Mainland: needed to climb trees to eat leaves
• Galapagos: grip slippery rocks to eat seaweed
*Darwin hypothesized that a small number of different plant and
animal species had come to the islands from the mainland. They
might have been blown out to sea during a storm. Once they
reached the island, they reproduced and eventually their offspring
became different from their mainland relatives.
Comparison Among the Islands
• Tortoises one on island had dome-shaped shells and on
another they had saddle-shaped shells
• Finches (small birds) varied from one island to another by
beak size/shape
• Beak shape is an example of an adaptation: trait that helps an
organism survive and reproduce in its environment
• Beak shape helped them get food
• Small sharp beaks could get insects easier
• Wide strong beaks were able to get seeds better
• What about the
tortoises?
Evolution
• Darwin spent another 20 years talking with other scientists,
gathering information, and thinking through his ideas
• He came up with the theory of evolution: gradual change in
species over time
Darwin also studied selective breeding to understand how
evolution might occur
Selective Breeding
• Used to selectively breed sheep to create fine wool
• Pigeons to get more tail feathers
• Darwin thought this type of breeding might happen in nature
but what was this process?
Natural Selection
• Darwin proposed that evolution occurs in nature through
natural selection
• Natural selection: individuals that are better adapted to their
environment are more likely to survive and reproduce than
other members of the species
Which would better survive if
there are rocks? Why? Trees?
Why?
Overproduction
• Species produce many offspring but not all of them will
survive
• All species need enough food, water, living space
Variations
• They have genetic variation, or different traits
• Sea turtles, iguanas, finches
Competition
• Resources are limited such as food
• Predators may eat them
Selection
• Environment has “selected” organisms with helpful traits
• Helpful variations may gradually accumulate in a species while
unfavorable ones may disappear
Environmental Factors
• Surroundings such as the iguanas
Genes and Natural Selection
• Variations result due to shuffling of alleles during meiosis
• Genes are passed from parents to offspring
• Without variation all members of a species would have the
same traits. Why is this a problem?