Three words that “tell” on us

Do we know what we’re talking about?

Especially when using these three words:


Unique has been dealt with (see post below).

Now–“theory”…as in “Evolution is JUST a theory.”


When we use the word “theory” with reference to anything in science, it does not mean what it means in other situations.

“I have a theory about how to get to the mall without getting stuck in traffic.”

“You’re full of it.”

“Hey, it just a theory.”

Fine.  “Theory” in this case means “an opinion.”  And it can be JUST an opinion.

But “theory” means something far different when referring to anything scientific.

The most glaring mis-use of “theory” is uttered by people who try to belittle the “theory of evolution.”  “It’s JUST a theory.”

In science, there are building blocks of findings.  At the  base are–facts.  For example, researchers have found that animals which are extinct harbor characteristics which exist in animals today:  a mammal’s hand & wrist, for example, closely resemble an extinct fish’s bones inside of a fin.  Among mammals themselves (a bat, a bear, a beaver), there is a very close resemblance between the bones of their hands.

Enough of these facts are discovered that scientists offer an hypothesis.  An hypothesis is a theory that is being tested.  The word “hypo” means “under”:  as in an “hypo-dermic” needle–“hypo” (under), “dermic” (skin).  An “hypo-thesis” means “a THESIS which is UNDER examination.”

A thesis is an argument being proposed. (In 1517, the maverick monk Martin Luther posed 95 arguments against the sale of indulgences, which became known as “The 95 Theses.”) The findings that the hand & wrist bones of extinct creatures are similar to those of living creatures results in an hypothesis:  The extinct fish are from the same family tree as creatures that are alive today on land.

The hypothesis holds up only if two conditions can be met.  One, findings must continue to be discovered which uphold the thesis.  Okay.  More & more fossils turn up hand structures that resemble the hand & wrist bones of living land creatures.

Fine.  But a second condition must also be met:  The hypothesis must be able to make predictions.  That is, if researchers keep looking, they WILL find a fossil of an amphibian which shows the same hand & wrist bones of living land creatures.  In other words, the fossil of the amphibian would confirm that some of the extinct fish at some stage of prehistory made their way onto land and became the ancestors of living land animals.

This finding HAS occurred.   Most famously, a discovery was made in the 1990s above the Arctic Circle in Canada.  A fossil amphibian was uncovered.  Its bone structure shows a clear link between fish and land creatures.  The fossilized amphibian was named “Tiktaalik rosea (check out its own web site).

The hypothesis–extinct fish are the ancestors of living land animals–has been confirmed so often by examining skeletal structure that the hypothesis now rises to a level of “law.”  A law, in science, means that a certainty has been established.  Something WILL happen according to the law.  Most famously, there is the “law” of gravity.

Isaac Newton declared this law:  Every object exerts a pull on every other object.  The bigger the object, the more forceful its pull on smaller objects.

Thus, we human beings are held down by the gravity of the Earth.  (In the Middle Ages, one of the comical assertions was that the Earth must be flat, because if it were round, people on the “under” side–the Southern Hemisphere–would fall off!  The law of gravity had not yet been discovered.  Human beings are held to the Earth by the planet’s mass, which exerts gravitational pull on any object which is smaller–like US.  Likewise, the planet itself is pulled by a larger object, the Sun.)  A law in order to be valid must explain what WILL happen under certain circumstances.  If I drop a pencil, it WILL fall to the floor.  Unless I’m in a space capsule.  In that case, there is not enough mass to draw the pencil to the bottom.  In the circumstance of outer space, the pencil will float.  The law is valid only under certain circumstances.

So there is this pyramid of findings in science:  At the base are facts; facts build up an hypothesis; an hypothesis is found to be so certain, it results in a law–like the law of gravity.

In the case of fossils, the law would be called “superimposition” (a law of geology).  Fossils which are farther down in the ground are older than fossils which are found in strata higher up; and the fossils down below belong in the same family tree as the fossils which are above them in strata.

Now, let’s say that there have been so many hypotheses which have held up, showing that extinct creatures are related to living creatures; laws have been declared, predicting that fossils which are found lower down in the geological strata will be older but still related to fossils which are found higher up.

At some stage of discovery, the facts, the hypotheses and the laws are united under one large umbrella which explains all of them:  THAT is a theory.

The theory of evolution by natural selection explains why all of it makes sense:  the facts of fossil discoveries showing similarity with existing creatures, the hypotheses about their common family tree, the laws predicting future findings…

Thus in the pyramid of findings–facts at the bottom, amounting to hypotheses, leading to laws–at the very peak is–the theory.  The theory explains the entire set of findings and predictions.

When somebody says, “Evolution is JUST a theory”–as though it’s JUST an opinion–with no more support than any other opinion like how to get to the mall faster–such people prove only that they don’t know what they’re talking about.  They don’t understand the meaning of the word “theory” as it is used in science.


(I am grateful for guidance on this post to the National Center for Science Education, which battles narrow-minded school boards and individuals who try to banish the teaching of evolution from public schools.  The former executive director, Dr. Eugenie Scott, has written brilliantly and clearly on the topic of what a theory means in science.)




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