What you will learn


 

Theory vs. theory. Is a scientific theory different from the everyday use of the word theory?

A scientific theory is accepted as a scientific truth, supported by evidence collected by many scientists. The germ theory of disease is a classic scientific theory in biology.

Scientific Theories

With repeated testing, some hypotheses may eventually become scientific theories. Keep in mind, a hypothesis is a possible answer to a scientific question. A scientific theory is a broad explanation for events that is widely accepted as true. To become a theory, a hypothesis must be tested over and over again, and it must be supported by a great deal of evidence.

Many people think that any idea that is completely accepted in science is a law, but that is not true. In science, a law is something that always applies under the same conditions. A theory is much more complex: it explains why something happens. A law only describes what happens. Additionally, people commonly use the word theory to describe a guess about how or why something happens. For example, you might say, “I think a woodchuck dug this hole in the ground, but it’s just a theory.” Using the word theory in this way is different from the way it is used in science. A scientific theory is more like a fact than a guess because it is so well-supported. There are several well-known theories in biology, including the theory of evolution, cell theory, and germ theory.

 

 

The Theory of Evolution

The theory of evolution by natural selection is a scientific theory. Evolution is a change in the characteristics of living things within a species over time. Evolution occurs by a process called natural selection. In natural selection, some living things produce more offspring than others, so they pass more genes to the next generation than others do. Over many generations, this can lead to major changes in the characteristics of living things. The theory of evolution by natural selection explains how living things are changing today and how modern living things have descended from ancient life forms that no longer exist on Earth. No evidence has been identified that proves this theory is incorrect. More on the theory of evolution will be presented in additional concepts.

The Cell Theory

The cell theory is another important scientific theory of biology. According to the cell theory, the cell is the smallest unit of structure and function of all living organisms, all living organisms are made up of at least one cell, and living cells always come from other living cells. Once again, no evidence has been identified that proves this theory is incorrect. More on the cell theory will be presented in additional concepts.

The Germ Theory

The germ theory of disease, also called the pathogenic theory of medicine, is a scientific theory that proposes that microorganisms are the cause of many diseases. Like the other scientific theories, lots of evidence has been identified that supports this theory, and no evidence has been identified that proves the theory is incorrect.

DID YOU KNOW?
The germ theory of disease was confirmed by Robert Koch and Louis Pasteur in the late nineteenth century through a series of experiments. They were able to establish that diseases like anthrax, rabies, plague, cholera, and tuberculosis were caused by microorganisms. Louis Pasteur and Robert Koch are rightly known as ‘Father of microbiology’ and ‘Father of bacteriology’ respectively for their contributions. 
 

 


Summary


Review

  1. Contrast how the term theory is used in science and in everyday language.
  2. Explain how a hypothesis could become a theory.
  3. Describe the evidence that proves the cell theory is incorrect.