4 – 1 What is evolution? Evolution

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4 – 1 What is evolution?

Evolution Evidence shows that the earliest living things on Earth were very simple organisms. In the billions of years that have passed, organisms have become more and more complex. Many species have become extinct and others have taken their place. A species is a group of organisms that look alike and can reproduce among themselves. Most scientists believe that new species develop from older species as a result of gradual change, or evolution. Evolution is the process by which living things over time.

Adaptations Living things can be found everywhere on earth, from the highest mountaintops to the deepest oceans, and from hot, dry desert to polar ice caps. Some bacteria live in rocks 1,609 m deep in Earth’s crust. How do different organisms survive such a wide variety of conditions?

Mutations Species evolve over time. Generally, a change in a species is caused by genetics. The each new generation, there is a new combination of genes. In time, new species can develop that will be different from their ancestors. Such changes take place over a very long period of time. These changes are needed to adapt to new environments.

Sometimes, however, something may cause a gene to change suddenly. A sudden change in the gene is called a mutation. If the mutation is helpful to the organism, it may be kept and passed on to the future generations. Eventually, the species changes. This may result in the evolution of a new species. If the mutation is harmful, the individual will probably die without passing the trait on.

The white python in the picture is an albino. Albino organisms do not have any pigments in their skin. It is a harmful mutation.

4-1 What is evolution?

Lesson Review

Write true if the statement is true. If the statement is false, change the underlined term to make the statement true.

1. Many scientists believe that new species develop from older species as a result of adaptation.

2. A change in a gene is called a mutation.

3. A trait of an organism that helps it survive in its environment is called an evolution.

4. The process by which organisms change throughout time is called evolution.

5. A group of organisms that look alike and can reproduce among themselves are a species.

6. If a mutation is helpful to an organism, it may die out before passing the
trait on.

Skill Challenge

Skills: analyzing, relating concepts

Study the diagrams shown below. On the lines provided, explain what features the cactus and the hawk have that allow it to survive in its environment.

Concepts and Challenges in Life Science, Teacher’s Resources CD-ROM

(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved. Life Changes Over Time: CHAPTER 4

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