U6 L1 Theory of Evolution by Natural Selection

Unit 6 Lesson 1 Theory of Evolution by Natural
Selection
Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 6 Lesson 1 Theory of Evolution by Natural Selection
Indiana Standards
• 8.3.1 Explain that reproduction is essential for the
continuation of every species and is the
mechanism by which all organisms transmit
genetic information.
• 8.3.5 Identify and describe the difference
between inherited traits and physical and
behavioral traits that are acquired or learned.

Indiana Standards
• 8.3.7 Recognize and explain that small genetic
differences between parents and offspring can
accumulate in successive generations so that
descendants may be different from their
ancestors.
• 8.3.8 Examine traits of individuals within a
population of organisms that may give them an
advantage in survival and reproduction in a given
environments or when the environment changes.

Indiana Standards
• 8.3.9 Describe the effect of environmental
changes on populations of organisms when their
adaptive characteristics put them at a
disadvantage for survival. Describe how extinction
of a species can ultimately result.
• 8.3.10 Recognize and describe how new varieties
of organisms have come about from selective
breeding.

Darwin’s Voyage
What did Darwin observe?
• Evolution is the process in which populations
gradually change over time.
• A scientist named Charles Darwin developed a
theory of how evolution takes place.
• Darwin formed the theory with the observations
that he had made on an almost five-year journey.

• On his journey, Darwin observed and collected
many living and fossil specimens.
• Darwin made his most influential observations on
the Galápagos Islands of South America.

• Darwin collected birds from the Galápagos Islands
and nearby islands.
• The birds on each island were different from the
birds on the other islands, and all were different
from the birds on the mainland.
• Darwin wondered if the birds had evolved from
one species of finch.

Darwin’s Homework
What other ideas influenced Darwin?
• Darwin was influenced by the ideas of many
scientists. These helped him develop his theory
about how populations change over time.
• Farmers and breeders select plants or animals for
breeding based on desired traits. This is called
artificial selection.
• A trait is a form of an inherited characteristic.

• Scientist Jean-Baptiste Lamarck thought that
organisms could bring about the changes they
needed to survive in the environment.
• He did not know that acquired traits do not
become part of an organism’s DNA and the traits
cannot be passed to the offspring.
• His idea that organisms’ traits help them survive
influenced Darwin’s theory.

• Geologist Charles Lyell theorized that small
changes in rock have collected over hundreds of
millions of years.
• Darwin reasoned that if Earth were very old, then
there would be enough time for very small
changes in life forms to collect over a very long
period of time as well.

• Darwin read an essay by Thomas Malthus that
suggested populations are limited by food
resources, disease, competition, and predation.

• Darwin reasoned that survivors probably had
traits that helped them survive in their
environment.
• Darwin thought that some of these traits would be
inherited by the offspring of the survivors.

Natural Selection
What are the four parts of natural
selection?
• Natural selection is the process by which
organisms that inherit advantageous traits tend to
reproduce more successfully.
• Plants and animals can overproduce, meaning that
they make more offspring than the environment
can support.
• Only some of them will successfully reproduce.

selection?
• Within a species there are natural differences, or
variations, in traits.
• Variations come from differences in genetic
material and can make an individual better able to
survive.
• Genetic variation is important for the survival of a
species.

selection?
• Individuals of a species try to get the resources
they need to survive.
• Darwin reasoned that individuals with a certain
trait might be more likely to survive long enough
to reproduce.
• As a result, the trait is “selected,” or is more
common in the next generation of offspring.

selection?
• An adaptation is an inherited characteristic that
helps an organism survive and reproduce in its
environment.
• As natural selection repeats from generation to
generation, these adaptations become more
common.
• Over time, a population becomes better adapted
to the environment.

Well-adapted
How do species change over time?
• An incredible diversity of life exists because
species have changed over time, or evolved.
• Populations evolve by becoming better adapted to
their environment by the process of natural
selection.

How do species change over time?
• Sometimes a population changes so much that the
population becomes a new species.
• Some of the adaptations that help species survive
are behaviors that help them to find food, protect
themselves, or reproduce.

Why is adaptation important for
survival?
• The traits that help an organism survive depend
on both the needs of the species and
environmental factors.
• Different environments have different factors.
• A green snake has a better chance of surviving to
reproduce in green grass than on a brown forest
floor.

survival?
• Changes in environmental conditions can affect
the survival of individuals with a particular trait.
• If no individuals are born with traits that help
them to survive and reproduce in the changed
environment, the species will become extinct.

survival?
• Extinction is when all of the members of a
species have died.
• The fossil record shows that many species have
become extinct in the course of the history of life
on Earth.

U6 L1 Theory of Evolution by Natural Selection

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U6 L1 Theory of Evolution by Natural Selection