Darwin’s Voyage

 Darwin’s Voyage

Darwin’s Observations

• As Darwin traveled around the world on a British naval ship, he was amazed by the incredible diversity of the organisms or species that he saw.

• Species– A group of similar organisms that can mate

with each other and produce fertile offspring.

Galapagos Island & South America

• Darwin was surprised that many of the plants and animals were similar to organisms on mainland South America, yet there were also important differences.

• Darwin inferred that a small number of different species had come to the island from the mainland and that eventually their offspring became different from the mainland relatives.

• Adaptation– A trait that helps an organism survive and reproduce.– Ex. Beak shape and size differences in the finches

Darwin’s Finches

Evolution

• Evolution– The gradual change in species over many

generations in order to become better adapted to the environmental conditions.

– Darwin proposed that evolution occurs by natural selection.

• Natural Selection– Process by which individuals that are better adapted

to their environment are more likely to survive and reproduce than other members of the same species.

Factors Affecting Natural Selection

• Overpopulation– Most species produce far more individuals than can

possibly survive.• Competition

– Offspring must compete for food and other resources to survive.

• Variations– Difference between individuals of the same species.

• Selection– Some variations make certain individuals better

adapted to their environment.– These will survive and reproduce, thus possibly

passing this allele onto their offspring.

Types of Selection

• Stabilizing Selection– Natural selection favors average individuals.– Reduces variation in a population.

• Directional Selection– Natural selection favors one of the extreme variations

of a trait.– Leads to rapid evolution of a population.

• Disruptive Selection– Favors both extreme variations of trait– Results eventually in no intermediate forms of the trait

and leads to the evolution of two new species.

Relating Natural Selection to Evolution

• Over a long period of time, natural selection can lead to evolution.

• Helpful variations gradually accumulate in a species, while unfavorable ones disappear.

• Ex. Faster turtles will be able to escape predators and thus might pass this trait onto their offspring. This species might then be marked by the “fast-swimmer” trait.

Role of Genes in Evolution

• NOTE: Only traits that are inherited, or controlled by genes, can be acted upon by natural selection.

• Ex. Color in moths during the Industrial Revolution

How Do New Species Form?

• Geographic Isolation– New species can form when a group of

individuals remains separated from the rest of its species long enough to evolve different traits.

– Ex. Kaibab vs. Abert’s Squirrel

• Continental Drift Theory– Emphasizes that Pangea breaking apart

resulted in geographic isolation which led to evolution of various species

Development of New Species

Patterns of Evolution

• Divergent Evolution– Pattern of evolution in which species that once were

similar to an ancestral species diverge, or become increasingly different

– Caused by populations adapting to different environmental conditions and eventually resulting in new species

• Convergent Evolution– Pattern of evolution in which unrelated species evolve

similar traits because they occupy similar environments in different parts of the world.

The Flip Side of the Coin

• Mutations or changes in the DNA are rarely helpful but are usually neutral, harmful, or fatal.

Summary Questions

• What is evolution? What did Darwin observe on the Galapagos Islands that he thought was the result of evolution?

• Explain why variations are needed for natural selection to occur.

• Describe how geographic isolation can result in the formation of a new species.

• Some insects look just like sticks. How could this be an advantage to the insects? How could this trait have evolved through natural selection?