Evolution is a fascinating phenomenon that has been the subject of countless scientific studies, debates, and discussions. But why do we call it a scientific theory? In this article, we’ll explore the meaning of the word “theory” in science and how it applies to evolution.

What is a scientific theory?

In everyday language, the word “theory” often means something that is unproven or uncertain. However, in science, a theory is an explanation that has been extensively tested and supported by a large body of evidence. According to the National Academy of Sciences, a scientific theory is “a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.”

How does evolution meet the criteria for a scientific theory?

Evolution meets all the criteria for being a scientific theory. Let’s examine each one in turn:

Well-substantiated: The idea of evolution has been extensively studied for over 150 years by scientists from many different fields. This research has produced an enormous amount of evidence supporting the idea that all living things on Earth share a common ancestor and have evolved over time.

Explanation: Evolution provides an explanation for how life on Earth has changed over time. It explains why there are similarities between different species (because they share common ancestors) and why there are differences (because natural selection favors traits that help organisms survive and reproduce).

Facts: There are many facts that support evolution, such as the fossil record (which shows how life on Earth has changed over time), comparative anatomy (which reveals similarities between different species), and molecular biology (which shows how organisms share DNA sequences).

Laws: Evolution is based on several laws of biology, such as the law of inheritance (which explains how traits are passed down from parent to offspring) and the law of natural selection (which explains how certain traits become more common in a population over time).

Inferences: Evolution is also supported by many inferences, such as the inference that all living things share a common ancestor (based on similarities in their DNA sequences) and the inference that certain traits evolved because they helped organisms survive and reproduce (based on observations of natural selection).

Why do some people reject evolution?

Despite the overwhelming evidence supporting evolution, some people still reject it. There are many reasons for this, including religious beliefs, lack of education or understanding of science, or simply a refusal to accept new ideas.

However, it’s important to remember that rejecting evolution does not make it any less of a scientific theory. The fact remains that evolution meets all the criteria for being a scientific theory and is widely accepted by the scientific community.


In conclusion, evolution is called a scientific theory because it meets all the criteria for being one. It provides a well-substantiated explanation for how life on Earth has changed over time and is supported by facts, laws, inferences, and tested hypotheses. While some people may reject evolution for various reasons, this does not change its status as a scientific theory.