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Lesson 2. The Theory of Evolution. By Natural Selection. Charles Darwin. Scientists had evidence that showed changes in species over time, but they didn’t know how. Charles Darwin was one scientist who struggled with this idea. Charles Darwin.

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The Theory of Evolution

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The theory of evolution

Lesson 2

The Theory of Evolution

By Natural Selection

Charles darwin

Charles Darwin

  • Scientists had evidence that showed changes in species over time, but they didn’t know how.

  • Charles Darwin was one scientist who struggled with this idea.

Charles darwin1

Charles Darwin

  • Darwin was a NATURALIST, a person who studies plants and animals by observing them.

  • He was not the first scientists to develop a theory about evolution, but his theory is the one best supported by evidence.

Charles darwin2

Charles Darwin

  • Darwin’s breakthrough came while on a voyage to the Galapagos Islands (near the equator off the pacific coast of South America).

  • Darwin noticed slight differences in animals living on each of the islands; he later decided that some varieties were different enough to be classified as different species.

Darwin s theory

Darwin’s Theory

  • Darwin noticed a relationship between each species and the food sources of the island it lived on.

Darwin s theory1

Darwin’s Theory

  • The species of tortoise that lived on an island with tall cacti had long necks, while the species of tortoise on an island with lots of short grass had short necks.

Darwin s theory2

Darwin’s Theory

Darwin s theory3

Darwin’s Theory

  • Darwin thought all the Galapagos tortoises shared a common ancestor that came to one of the islands millions of years ago.

  • He knew that members of the same species each have slight differences called VARIATIONS.

  • Darwin didn’t know about heredity, but he realized that variations in populations could help explain how the different species of Galapagos tortoises and finches evolved.

Darwin s theory4

Darwin’s Theory

  • Darwin knew that food is a LIMITING RESOURCE, so members of a species that live in the same area compete for food.

  • If a variation benefited a tortoise, allowing it to compete better for food than other tortoises (more “fit” to its environment), the tortoise was more likely to live longer, reproduce more, and pass on its variations to its offspring.

Natural selection

Natural Selection

  • NATURAL SELECTION: Individuals within a population that possess variations which help them survive in their environment tend to live longer, compete better, and reproduce more than individuals that do not have the beneficial trait.



  • An ADAPTATION is an inherited trait that increases an organism’s chance of surviving and reproducing in its environment.

  • Scientists classify adaptations into three categories.



  • STRUCTURAL ADAPTATIONS involve color, shape, and other physical characteristics.



  • BEHAVIORAL ADAPTATIONS involve the way organisms behave or act.



  • FUNCTIONAL ADAPTATIONS involve internal body systems that affect biochemistry.

Environmental interactions

Environmental Interactions

  • A structural adaptation that aids members of a species in blending in with their environment is called CAMOUFLAGE.

Environmental interactions1

Environmental Interactions

  • An adaptation in which one species resembles another species is called MIMICRY.

Environmental interactions2

Environmental Interactions

  • The living and nonliving parts of the environment are always changing; species that cannot adapt to such changes will become extinct.

Natural selection vs artificial selection

Natural Selection vs. Artificial Selection

  • Darwin’s theory of natural selection predicts that species will develop adaptations, which explains why we see such a diversity of organisms that are perfectly suited to thrive in their environment.

Natural selection vs artificial selection1

Natural Selection vs. Artificial Selection

  • SELECTIVE BREEDING is the practice of breeding organisms for desired characteristics.

Natural selection vs artificial selection2

Natural Selection vs. Artificial Selection

  • Darwin realized that natural selection and artificial selection are similar processes.

    • In natural selection, nature causes the changes in the species.

    • In artificial selection, humans cause the changes in the species.

Natural selection vs artificial selection3

Natural Selection vs. Artificial Selection

  • Artificial selection explains and supports Darwin’s theory.

Common misconceptions about evolution

Common Misconceptions about Evolution

Common misconceptions about evolution1

Common Misconceptions about Evolution

Jean-Baptiste Lamarck

Common misconceptions about evolution2

Common Misconceptions about Evolution

Common misconceptions about evolution3

Common Misconceptions about Evolution

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