Chapter 6-Change Over Time
Study Notes
Big question: How do life forms change over time?
Lesson 1-Darwin’s Theory
Charles Darwin was a naturalist. He took a five-year voyage on his ship, the HMS Beagle, and
noticed great diversity. He is most famous for traveling to the Galapagos Islands. He thought the
fossils of the giant sloths resembled the bones of smaller modern sloths.
A species is a group of organisms that can mate together and produce fertile offspring.
A fossil is the preserved remains or traces of an organism that lived in the past. Darwin noticed.
Beak types, something Darwin noticed in finches, is an example of an adaption. An adaptation
is a trait that increases and organisms to survive and reproduce.
Darwin’s Hypothesis
Darwin hypothesized that species change over many generations and become better adapted to
new conditions.
Evolution is the process of change over time.
A scientific theory is a well-tested concept that explains a whole range of observations. Darwin
concluded that the Galapagos Islands changed over time.
Artificial Selection
In artificial selection, only organisms with the desired traits are bred. Darwin bred pigeons with a
desired trait. Over time, more pigeons with the desired trait appeared. Darwin believed that this
is what happens in nature.
Natural Selection
Natural selection is the process by which individuals that are better adapted to their environment
are more likely to survive and reproduce more than other member of the same species.
Factors that affect natural selection:
-overproduction - producing more offspring than can possibly survive
-variation - any difference between individuals of the same species
-competition - compete for food, space, and other resources
Darwin proposed that over a long time, natural selection can lead to change. Helpful variations
may accumulate in a species, while unfavorable ones may disappear.
Change in Environment
Changes in environment can affect an organism’s ability to survive.
Variations in the species are due to mutations or DNA recombination.
Lesson 2-Evidence of Evolution
Scientists have discovered that:
-fossils
-similarities in early development
-similarities in body structures
-similarities in DNA
Provides evidence that living things have changed over time.
Similarities in early development
Homologous structures-similar structures that related species have inherited from a common
ancestor
Lesson 3-Rate of Change
A new species can form when a group of individuals remains isolated from the rest of the
species long enough to evolve different traits that prevent reproduction.
Scientists have developed two patterns to describe rate of change: gradualism and punctuated
equilibrium
gradualism - small changes that add up to major changes over a long period of time.
-slow and steady
punctuated equilibrium - species evolve during short periods of rapid change
-might be caused by isolation, a natural disaster, or a response to an environmental change.