The Theory of EvolutionBy Natural Selection

Lesson 2

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• 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 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 noticed a relationship between each species

and the food sources of the island it lived on.

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 Theory

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 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: 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.

Adaptations• 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.

Adaptations

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

Adaptations

• BEHAVIORAL ADAPTATIONS involve the way organisms behave or act.

Adaptations

• FUNCTIONAL ADAPTATIONS involve internal body systems that affect biochemistry.

Environmental Interactions• A structural adaptation that aids members of a

species in blending in with their environment is called CAMOUFLAGE.

Environmental Interactions• An adaptation in which one species resembles

another species is called MIMICRY.

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• 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 Selection• SELECTIVE BREEDING is the practice of

breeding organisms for desired characteristics.

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 Selection

• Artificial selection explains and supports Darwin’s theory.

Common Misconceptions about Evolution

Common Misconceptions about Evolution

Jean-Baptiste Lamarck

Common Misconceptions about Evolution

Common Misconceptions about Evolution