GED Science Test: The Theory of Evolution

By Murray Shukyn, Achim K. Krull

You will need to know the basics behind the theory of evolution for the GED Science test. Evolution is a scientific theory that explains how the diversity of living things developed in response to various environmental factors and how they adapt to changing conditions over time. But evolution itself is more fact than theory. You can observe it taking place in the field of medicine, for example, as bacteria develop resistance to antibiotics.

Exterminators witnessed evolution at work in the 1980s when a certain poison that had been very effective in killing cockroaches stopped working. The cockroaches had developed a genetically programmed aversion to the corn syrup used to attract them to the poison.

Scientists are still uncertain of how, specifically, evolution occurs. Darwinism is the most accepted theory today. Darwin’s theory is that genetic mutations occur randomly. Through a process of natural selection or survival of the fittest, mutations that are beneficial to the organism’s survival are passed along to future generations, while those that are detrimental fail to survive. Selective pressures include disease, competition for food and other resources, and environmental factors.

For example, near the equator, genes for dark skin have an advantage over those for light skin because dark skin has more melanin to protect against damage from intense ultraviolet (UV) radiation. In colder areas with less intense sunlight, genes for lighter skin have an advantage because lighter skin allows more sunlight to penetrate, which drives the production of vitamin D, which is needed for strong teeth and bones.

Investigating common ancestry

Common ancestry is the scientific theory that all known living organisms arose from a common ancestor. By closely examining DNA, scientists can determine how closely related two species are and estimate the time when the two species diverged. These relationships are often illustrated in the form of a cladogram.

A cladogram.

A cladogram.


Crocodiles and birds are related. They’re not sibling related but are very distantly related, both sharing a common ancestor that lived around 240 million years ago. Using the Internet for research:

  1. Develop an outline of information on the topic of “Guess who was in the family a long, long time ago?”

  2. From your outline, write a one- to two-page essay.

  3. Based on your essay, develop four or five questions that can be answered from the information in your essay and some general knowledge. Develop answer choices and make sure the correct answer is based on information in your essay and not something you remembered from your research.

This exercise is similar to the process an examiner would use to develop questions for a test. Now that you can see a process that’s not magical or mystical, relax; with preparation, you can do well on these tests.