The process of developing scientific theories is a crucial part of understanding the natural world. Here we will examine how biological theories develop. At the end, you can test your knowledge with a brief quiz.

What Are Theories?

You’ve most likely heard the word theory used in conversation, and have used it yourself. The common use of ‘theory’ suggests it to be a guess or an idea that someone comes up with as an explanation for something. For example, you’re watching Lost, the TV show about survivors on a mysterious island, and you turn to your friend and say, ‘My theory is that the island is a portal to another dimension.’ You’ve come up with this idea based on some apparent evidence – the events and actions of the characters on the show – giving you reasons behind your idea.

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In the scientific community, however, the definition of theory is actually quite different. A scientific theory also has substantial evidence to support it, but of equal importance, it must be tested repeatedly for validity.

As much as you might have reasons behind your explanation for Lost, your idea cannot be tested, and is therefore not truly a theory, in the scientific sense. Your idea is actually a hypothesis, a proposed explanation that serves as a starting point for further investigation.

After gathering data, testing, and getting consistent and irrefutable results, a hypothesis can eventually become a theory, but most hypotheses do not. As new results or evidence roll in, many hypotheses are nullified, or found to be incorrect, and new ones take their place.

Theories vs Facts

A common misconception about theories is that they are weakened versions of facts. Two incorrect notions follow from this: that theories are not entirely proven and facts are, and that theories get promoted to facts once they are proven.

In science, facts are observations that are repeatedly shown to be true, while theories explain the behavior or nature of those facts. For example:

FACT: objects fall downward. We can observe this countless times.

THEORY: the Theory of Gravity, a mathematical formula describing attractions, explains why this happens.

FACT: The sun rises and sets.

THEORY: The Theory of Heliocentrism, that the Earth orbits the Sun, explains why this happens.

Becoming a Theory

The establishment of a theory is an extremely rigorous process in science. Because theories describe the nature of facts, they must have endured extensive testing and reflect the most accurate and up-to-date knowledge in the field. All theories:

  • started with an observation,
  • had someone come up with a hypotheses to explain what was observed,
  • went through many rounds of testing, with no result disproving the hypothesis.

This does not mean that new facts and information cannot change a theory; in fact, the ability to be modified with new information is an important characteristic of theories, indeed for science! Becoming a theory is the highest level of regard and prestige an idea can achieve.

The process of establishing a theory. Notice how a theory must be able to be modified when new evidence arises!

Major Biological Theories

There are four major theories that encapsulate our current knowledge of living things.

1) Evolution by natural selection – Organisms that are better adapted to their environment will produce more offspring and therefore be more successful. This theory explains why we see the fact of evolution, or organisms changing over time.

Specialized beaks make different species of birds better able to survive and pass on their genes.
natural selection

2) Homeostasis – how living things regulate their internal environment, things like temperature, water, pH, or oxygen levels. This explains why our bodies stay in balance even in changing environments.

Reptiles need to bask in warm light in order to maintain temperature homeostasis.

3) Cell Theory – cell theory describes the cell as the most basic unit of all life. It has explained the ‘stuff’ of what life is made out of.

An early drawing of a cell in the establishment of Cell Theory.

4) Gene Theory – traits are passed from parent to offspring by way of genes. This theory explains what it is that makes offspring look or act like their parents.

Puppies inherited genes from their mother to make them black and white
dog genes

Each of these theories were developed through multiple studies by many different contributing scientists. Though one scientist is often credited for coming up with the hypothesis that later became a theory, it’s all a collaborative effort by many people over decades, or even centuries!

Lesson Summary

In science, a theory is an explanation for a body of facts. It is built upon a successfully tested hypotheses and collaborative efforts of multiple scientists. While a fact is an irrefutable observation, a theory explains the nature of facts, and is thus not a weakened version of a fact, nor can it be promoted to fact. A theory is actually the highest level of a scientific idea!

There are four major theories in the field of biology: evolution by natural selection, homeostasis, cell theory, and gene theory. Each of these theories consistently explain all presently-known and relevant facts.

A theory must be able to be modified in light of new evidence, and be the product of wide scientific consensus. In science, nothing is ‘just a theory’!