Life Science Theories

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  • 0:01 Theories
  • 1:02 Theories are Created
  • 3:03 Cell Theory
  • 4:36 Theory of Evolution
  • 5:54 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

In the life sciences there are many theories that explain how life works. However, before these theories became widely accepted, they had to be put to the test. In this lesson, you will learn how ideas become theories.


Do you ever wonder what happened to the dinosaurs? Dinosaurs became extinct about 65 million years ago. Over the years, scientists have come up with a number of ideas to explain their disappearance. Some proposed that an asteroid struck the earth, and the impact caused a massive cloud of dust that blocked out the sun. Other scientists think that an ice age occurred that made it impossible for the dinosaurs to live.

Because dinosaurs died out so long ago, we might never know for sure what happened to them, but that doesn't stop scientists from developing theories, like the Asteroid Impact Theory and the Ice Age Theory. Theories are tested explanations that have been generally accepted by the scientific community. In this lesson, we will learn how theories get developed. We will also discuss a couple of theories that are important to life sciences, namely The Cell Theory and The Theory of Evolution.

Theories Are Created

When scientists are curious about something, they use the scientific method to come up with plausible ideas. The scientific method is useful because it's an organized way of studying something. This process always starts with the first steps, which are asking questions and making observations. Let's say you were the first people to stumble upon the fossils of a huge dinosaur. You know that an animal that big no longer exists. This could raise the question: why do dinosaurs no longer walk on the earth?

Your curiosity would lead you to the next step of the scientific method, which is forming a hypothesis. A hypothesis is an idea that can be tested. For example, a scientist that believes dinosaurs were wiped out by an ice age could develop a hypothesis that states: if an ice age occurred 65 million years ago, then it could have caused the extinction of dinosaurs. The scientist could then look for evidence to test the hypothesis by doing things like analyzing samples of the layers of the earth. After the data was collected and studied, the scientist would form a conclusion. If he found evidence that supported his hypothesis, then his hypothesis is said to be correct.

Now this is where we get into the difference between a hypothesis and a theory. You see, the conclusion of one scientist might be enough for him to say that his hypothesis is correct; however, theories require widespread acceptance from the scientific community. For a hypothesis to become a theory, other scientists would need to test the same hypothesis and come up with the same results. This is how we got the Ice Age Theory to explain the demise of the dinosaurs. Many scientists have found evidence that an ice age occurred around the time that dinosaurs became extinct, so the scientific community accepts this as a valid theory.

Cell Theory

Now that you understand how a theory gets developed, let's take a look at a theory that is very important to the life sciences. It's called the Cell Theory, and it actually has three parts. The theory states that all living things are made of cells, cells are the basic organizational units of living things and cells come only from other living cells.

Now, chances are you have used a microscope to look at a cell. In fact, cells might seem a bit boring nowadays. But remember that the earliest versions of the modern-day microscopes didn't come into existence until the 1600s. Can you image the questions that would be popping into your mind if you were one of the first scientists to see cells under a microscope?

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