What is a Scientific Theory?

Unless you limit yourself to the best books and websites, it won’t take long before you’ll run into someone who dismisses the whole shebang of evolution as ‘just a theory.’ A hunch. You might as well consult the Magic Eight Ball. “Is evolution true?” Flip the ball over. “Outlook not good.” The argument here is that there are other, and possibly better, explanations. And if there are other explanations for the diversity of life on earth shouldn’t we be responsible and air those too? If evolution is just a best guess then shouldn’t other guesses be allowed to compete?  It’s wrong-headed but fair game, really. If there are other plausible ideas that fit all of the evidence, then we should consider them. 

So what is a theory?

Merriam-Webster defines a scientific theory as ”a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena.” This is opposed to ‘abstract thought. Speculation.’

The American Museum of Natural History characterizes a theory as something that;

“not only explains known facts; it also allows scientists to make predictions of what they should observe if a theory is true. Scientific theories are testable. New evidence should be compatible with a theory. If it isn’t, the theory is refined or rejected. The longer the central elements of a theory hold – the more observations it predicts, the more tests it passes, the more facts it explains – the stronger the theory.”

How Do Scientists Define a Theory?

There is no single definition and no set rules for what constitutes a theory. But the elements of a theory are facts, observations, and hypotheses that combine disparate parts into a many-stranded whole. Generally, a theory includes most of these components:

Well-established observations that generally occur in every known occurrence
The theory is strengthened by new findings
The theory is falsifiable
The theory is flexible
The theory tends to incorporate findings from several disciplines
The theory provides predictive power for further exploration and study

Note, too, that confidence in theories changes over time. Phrenology was the rage in the early nineteenth century. Phrenology is the ‘science’ of predicting morality and intelligence by measuring the outside of the skull. There is a putative basis for the study:

1. The brain is the organ of the mind.
2. The mind is composed of multiple distinct, innate faculties.
3. Because they are distinct, each faculty must have a separate seat or “organ” in the brain.
4. The size of an organ, other things being equal, is a measure of its power.
5. The shape of the brain is determined by the development of the various organs.
6. As the skull takes its shape from the brain, the surface of the skull can be read as an accurate index of psychological aptitudes and tendencies.

Given these premises, there is a logic to the science. But as medicine and biology and psychology emerged as true sciences, phrenology was soon seen to be a fallacy. The premises didn’t hold. New facts didn’t fit into the theory. Predictions based on what was ‘known’ weren’t found to be true. Today, phrenology is a curiosity that is tossed into the history bin.

Just a theory?

Is this a butterfly, a Spicebush Swallowtail, or a Papilio troilus? All are true. It all depends on if you are using colloquial or scientific terminology.

Must a Theory Be Proved?

What does it mean for a theory to be proved? The fact is that we are never done with a theory. Or with anything in science, for that matter. Every experiment or observation or equation adds to or detracts from the general idea. It’s more accurate to say that we build confidence in a theory. Still, there was a time when serious and respected scientists measured skulls with a high confidence in their ‘results.’ Did that make it true? No. Continued and further research and observation finally showed that there was no merit to the idea and it fell from use.

Nor is a theory a fact. It is an observation about a collection of facts. So it cannot be proved like a syllogism. The National Center for Science Education answers this misunderstanding with the following correction:

“[This misunderstanding]…implies that theories become facts, in some sort of linear progression. In science, theories never become facts. Rather, theories explain facts. [Another] misconception is that scientific research provides proof in the sense of attaining the absolute truth. Scientific knowledge is always tentative and subject to revision should new evidence come to light.”

Can a theory be both right and wrong? In a sense, yes, depending on the framing. The backbone of evolutionary theory is considered fact by most biologists. But controversy abounds around the edges. This is exactly what we expect. Science is always working at its edges. No one is wondering about the circulatory system anymore. No one is wondering about what drives the heart to beat. We don’t do work on the things we know. As soon as one question in science is answered, a series of new questions are asked. This is where science lives.  And it’s at the edge that we often get things wrong. Why wouldn’t we? We don’t know so lots of goofy ideas are proffered. Some are useful and some come to naught. That’s why we study them. We study, we posit, we hypothesize, and we make best guesses based on the evidence. Many or most of these ideas will fit into our theory and some won’t. Occasionally a theory is completely overturned. The most famous overturned idea is the geocentric universe. It is natural to think that the sun and stars revolved around the earth. The sun rises and sets in different places but the earth seems to stand still. If the earth is spinning then why don’t we feel wind? And for fifteen-hundred years, Christians, who held the scepter of truth, proclaimed the earth as the center of the universe. It wasn’t until Copernicus began publishing his astrological work in the mid-sixteen century that the idea was overturned.

Why does science define a theory in a special way?

Science goes to great lengths to define things in specific ways. This is partly to be very clear about what we are explaining. When I worked in research and we wrote papers we defined exactly what strain of rats we used and where we purchased them. If needed, we could produce the lot number from their birth record. The layman might think that rats are rats. The researcher knows that this is not true. Science usually works from the specific and detailed outward. Once we have a glimpse of an answer with the specific we expand out to test and see if the story will hold for the group. It often doesn’t. Or think of this: a dad might tell his child to ‘take a swig of cough syrup.’ Does it surprise anyone that the label reads ‘ingest 2 cc per hour for a maximum of eight hours?’ That’s the dosage tested and that’s what the drug company can stand behind.

The Devil’s Theory

Just a Theory?The statement is often made by detractors that ‘evolution isn’t a fact: it’s just a theory.’ Sometimes, the detractor is just mistaken and doesn’t understand the use of the scientific term ‘theory.’  Sometimes, it’s used in this way by someone who should know better.  Of course, the question can be legitimate and there is confusion that rests on a collision between technical and colloquial language. In everyday terms, a theory is a best guess. “You wanna know my theory? His head’s too messed up with his divorce to maintain his batting average.” But in scientific terms, a theory has a specific meaning that has nothing to do with guessing. It is an over-arching explanation that unifies a set of laws and observations. It is not a fact but an explanation of how facts fit together. It makes sense that science uses technically defined terms. No one is surprised that we use specific language to define specific things. That certain creationists purposefully conflate terms to cause confusion only reveals their motives.

That evolution is a theory is used by some creationists who hope to muddy the waters when they speak or write. It’s similar to the serpent’s question in the garden: “Did God actually say, You shall not eat of any tree in the garden?” No, God did not make that command. What he said was that Adam and Eve could not eat from the tree that is ‘in the midst of the garden.’ The serpent hopes that Eve doesn’t catch the bait and switch. When creationists comment that evolution is only a theory, they are doing the same thing. They hope that no one in the audience will catch that they are using the word ‘theory’ differently than scientists do.

Other Theories?

Virtually all facts about the natural world fall under some sort of theory. Beside the Theory of Evolution, other examples include quantum theory, game theory, and the general theory of relativity. None of these theories seem to bother anyone which reinforces the statement that evolution is threatening primarily because it challenges certain religious and cultural beliefs about our world and ourselves.

Are there other options?

There are other explanations for the diversity of life on earth. None are scientific. My favorite, indeed my favorite explanation for a multitude of things, is the brain in a vat. This position states that your entire life is just a series of neural inputs to make you believe that you are experiencing something outside of yourself. It’s part of the basis for the movie The Matrix. Each religion has it’s own explanation, too. One Hebrew tradition is that God created all life within the six days of creation. God made and Adam named. Certain modern Christian groups argue strongly for a literal interpretation of this belief as both essential to their faith and as most consistent with observations of the world. Traditional Hinduism teaches that the universe is repeatedly created and then destroyed and that we all exist in an eternal boom-bust cycle seeking enlightenment. Other religions including Voodoo, Santeria, and forms of animism typically mix modern religion, often Catholicism, with local customs to create their own stories of Sun-gods and Sky-daughters.

Should these traditions be taught? Yes. They are fascinating subjects that tell us something about human beings and about society. It’s important for an educated population to know the history of their people and of the world. It’s even more important as the world continues to shrink due to the internet. Should these stories be taught in biology class? No. They are not scientific in nature and fail all tests of scientific inquiry.

Want more foundations of evolution? Go here to read about the world view required by science.


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