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Answer the following question:
Two species of mice live in a field in the middle of
East Texas. One mouse species is white with black
spots, the other is brown with white spots.
After a year, the population of white mice has
dramatically decreased, while the population of
the brown mice has slightly increased.
Why might this be happening?
CO: I will analyze how evolution
occurs in a population. I will
examine evidence for evolution.
LO: I will talk about evolution with
the class. I will write notes about
Let’s chat about our potato farms!
Evolution: What is it?
Evolution: change in heritable traits of a
population across generations (over time).
Charles Darwin: contributed more to our understanding
of evolution than anyone else.
• Darwin traveled, made observations and collected evidence that
led him to propose his revolutionary process in a book called On the
Origin of Species
Population size is limited by
environmental resources.
*What are some examples
of environmental resources?
Fitness: the ability of an organism to survive and
Fitness is the result of adaptations.
Adaptation: any inherited characteristic that
increases an organism’s chance of survival.
Successful adaptations:
- enable organisms to become better suited to
their environment
- increase an individual’s ability to survive and
The Primary Mechanism of
Natural Selection
Natural selection: the process by which individuals with
characteristics that are not well suited to their
environment either die or leave few offspring.
1. Also referred to as survival of the fittest.
2. It is not seen directly, but only observed as changes
in a population over a long time.
Bunny Simulation
If only one species is considered the "fittest", why do we still have so many
variations among species? Why do some birds have very long pointy beaks,
while other birds have short flat beaks?
Evidence for the Theory of
Evidence for evolution can be found in:
1. the fossil record
2. biogeography (the geographical distribution of living species)
3. homologous structures of living organisms
4. similarities in early development, or embryology.
5. molecular (DNA) homologies
1. Fossil record
By comparing fossils from older
rock layers to fossils from younger
layers, researchers have
discovered many hundreds of
transitional fossils that document
various intermediate stages in the
evolution of modern species from
organisms that are now extinct.
2. Biogeography: study of the
geographical distribution of plants
and animals
Darwin observed this with finches
and tortoises in the Galapagos
Islands. He noticed that there were
several different species of
birds/tortoises on the islands that
were similar to each other, but had
different adaptations. He thought
that they evolved from a common
ancestor to best fit the environment
of the island they were on.
We can see this in other species
around the world too.
3. Homologous structures: bones and muscles that have
similar structures but perform different functions
4. Embryonic Homologies: Different organisms develop
from similar starting forms (embryos)
5. Molecular Homologies: similarities in DNA sequences
among different organisms
*Because organisms evolved from a common ancestor, we
find similarities in the DNA sequence of all living
*The more of a DNA match we see, the closer of a
relationship the organisms have.