Only a Theory?

By Laurie Hatton (in collaboration with her local Brights Community Cluster)

Sherlock Holmes commonly stated to Watson, “I have a theory.” The word “theory” means that something is a guess or speculative idea. Right?  Well, yes it can. However, when a scientist uses the term theory, he or she means something totally different.  A scientific theory is an idea that has a lot of evidence to back it up – no guessing involved.

NACA Physicist Studying Alpha Rays

Photo: NASA

Scientists start with a hypothesis – an educated guess based on observation.  A hypothesis can be either supported or refuted through testing or observation. Key hypotheses are tested over and over by independent researchers.

When people say, “I have a theory about that,” what they often mean is that they have a hypothesis.

A scientific theory is much more than a hypothesis.  It is a hypothesis that has been tested and shown to be true beyond any reasonable doubt.  Either that or it is an all-encompassing explanation of a set of well supported hypotheses.  Scientific theories can be shown to be false. But, by the time an idea has made it to “theory,” the evidence is so strong that this almost never happens.  Scientists may argue about the details of the supporting evidence, but rarely about the theory itself.

People used to believe that the sun, moon and stars revolved around the Earth. Evidence now shows that the Earth is a tiny speck orbiting a relatively average sized star, hurtling along on the inside edge of one of the spiral arms of the Milky Way galaxy, which is one of hundreds of billions of galaxies in the universe. These are theories.  They are supported by rigorously tested hypotheses.  In this day and age, people don’t seem to have a problem believing Earth’s puny position in the universe.

Up until very recently, most people believed that the continents had always been where they are now. It was generally considered “just a coincidence” that they looked as though they fit together like a jigsaw puzzle. It was suggested in the late 1500s that they might have once been joined, and since the 1960s, most people understand that the continents were once one, and have split and moved apart or crashed into each other over billions of years, and are in fact still moving. There is strong evidence for the theory of plate tectonics.

Evolution by natural selection is a theory.  It is supported by many lines of evidence. This evidence includes the obvious fossil record, but also genetics, comparative anatomy, and the geographic distribution of species, among many other things. Prior to Darwin’s On The Origin of the Species by Means of Natural Selection, some scientists suspected that evolution had happened.  However, they could not explain how it happened.  Darwin gave us a clear overarching explanation.

Next time you hear someone use the word theory, play Sherlock Holmes; do they really mean hypothesis?

I recently saw a bumper sticker that read, “Evolution is only a theory.  Just like..um..gravity.”  Oh, wait.  It’s on the back of my car.

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32 Responses to Only a Theory?

  1. Mark Anderson says:

    Not only is gravity only a theory, but its mechanism is much less understood than that of evolution.

    Which I think proves that in fact, gravity doesn’t exist, and instead, the earth sucks.

  2. Williasm B. Secor, Ph.D. says:

    No, evolution is not a theory, has been proven over and over again and is still being proven, every day, observe microscopic organisms for proof plus many other species. The evolution controversy is an argument from religion, religions which are rotting and empty at their core. Noah, nonsense, the Bible is metaphor, stores, allegories made up by men thousands of years ago. America is a very ignorant, uneducated nation, we are a joke.

    • John C. Spengler says:

      Dr. Secor,

      Although I understand your position I wish to clarify some misconceptions. First, Evolution is a theory; a scientific theory. This statement in no way diminishes its importance or relevance. Our understanding of Natural Selection, The Modern Synthesis, genetic drift, sexual selection, etc., etc. are collectively known as The Theory of Evolution. Second, evolution is also a fact. That organisms have changed over the 3+ billion years of life on earth is incontrovertible. Our understanding of how evolution works verifies this fact over and over again. Third, as scientists, we must remain as objective as possible and be open to new data and interpretations of that data as it becomes available. As such, we should never claim that evolution, or any other scientific theory for that matter, is absolutely “proven”. Rather, we should say, that having tested and verified them so often, that they are “proven beyond a reasonable doubt”. This last line of reasoning came from my late friend, mentor and colleague Dr. John A. Moore. John was Professor Emeritus at the University of California, Riverside and a leader in Evolution education.

      • Justin says:

        I wish there were a like button on here. You stated that perfectly, John. Stating that evolution is not a theory is equally as wrong as stating it’s ‘only’ a theory.

      • Kim says:

        Exactly, this is what separates the scientific mind from the religious. You should always have an open inquiring mind ready to except new evidence which can either be substantiated and included or dismissed.
        If you ever close that open door and believe without question it would be no better than believing in the fairy tail stories of religion

  3. Alfredo Quintero says:

    This article hits the nail on the head. The abuse of the word “theory” in every day conversation is pervasive. Had not thought about Sherlock Holmes stories as a precedent. I think journalists should use the word “hypothesis” when speculating about causes for accidents, especially during the very early stages of an accident investigation, instead of writing/talking about this or that theory. People not familiar with the scientific method may find it difficult to distinguish between both, and thus the “just a theory” argument may sound as if it has a point, when in fact it is an empty argument.

  4. Dan A Wilson says:

    When I was still an active (not retired) university professor, every year I spent WAY TOO MUCH time trying to make my new students understand why “That’s just a theory” made no real sense in the world of science. When a hypothesis has been subjected to a very large number of attempts to disprove it — one of the main problems with college-student teaching about the difference between hypotheses and theories is that you never have the chance to prove your hypothesis or theory “beyond any shadow of a doubt,” because there’s always the possibility that disconfirming evidence will appear — (you can’t prove that hens don’t lay eggs by showing someone a million pictures of hens not laying eggs; all that’s required is one single picture of a hen laying an egg, and the evidence of the million pictures is dust), but the farther we go down the path of looking for disconfirming evidence without finding any, the more confident we become that a group of hypotheses has become a theory, and that the theory is factual (until and unless really irrefutable evidence disconfirms it).
    The longer a theory survives all significant attempts to find any evidence to disprove it, the closer we, as scientists, come to regarding the theory as fact. One of my most pleasurable moments of watching TV in my whole life (well, since the ’50s) was when the late Carl Sagan, in the course of the original COSMOS series, said, on national and international television, to millions of viewers, “Evolution is NOT ‘just a theory;’ it’s a FACT’!”

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  5. Leonard Eisen says:

    I tend to explain the difference between the terms fact, hypothesis and theory a little differently, and I find that it is easier to explain the differences with respect to gravity and to then apply them by analogy to evolution.
    A fact is something that we have determined to be true by repeated observation and/or experiment. A hypothesis is an attempt to explain facts and to put them in some framework that allows us to make predictions about things that we have not yet been able to observe. If a hypothesis does make such predictions and remains consistent with all experimental and observational evidence despite our best efforts to falsify it, we call it a theory.
    Gravity is a fact. We can all do an experiment to confirm it by knocking something off our desk and watching it fall to the floor. If we have access to the proper equipment, we can observe evidence of moons orbiting planets and planets orbiting stars. A theory of gravity attempts to explain these observations and predict results that we have not yet observed.
    Newton’s theory of gravity was consistent with all the facts about gravity that were known while he was alive. His theory stated that all masses attracted each other with a force inversely proportional to the square of the distance between them. Einstein came up with a different theory, general relativity, stating that mass/energy warps space/time. It turns out that Einstein’s theory made some correct predictions that Newton’s theory did not, so it supplanted Newton’s theory as the best one that we have to explain gravity. Newton’s theory actually turned out to be a simplification of Einstein’s theory if things didn’t move to fast and were not too massive.
    General relativity still has problems, as it is not consistent with quantum mechanics, so people are now searching for “quantum” theories of gravity. Having said all that, none of the modifications to older theories change the observed fact that if you knock something off your desk it will fall, and that planets orbit stars. No rational person would jump off a building because “gravity is just a theory.”
    Evolution is a fact based upon copious amounts of observational and experimental evidence. We can look at the fossil record, at changes in the genetic code over time in the same species or between different species, at anatomic, physiologic and biochemical similarities between species, etc. We can directly observe changes in natural populations that occur over short periods of time. We can do experiments that drive evolution in bacterial or insect populations based upon man made modifications to the organism’s environment. Many books have been written outlining the evidence for evolution.
    Subtle changes may (and will) happen to the theory that we use to explain how evolution works. In the absence of clear experimental or observational evidence, we may argue over what fraction of random mutations are harmful, neutral or beneficial. We may argue over whether evolution happens to populations as well as to individual organisms. The overall fact that evolution exists is in no way modified by these arguments, or their eventual outcomes.

    • Your words have abundant clarity, consistency, and coherence. Agreed: evolution, just like gravity, is a fact evidenced by copious examples of regularly observable situations. And a theory is indeed a set of consistent, albeit revisable, hypotheses not only recurrently supported by facts but also currently resistant to refutation. There are now unfalsified theories about gravity and evolution that, however revisable they are, are as best as currently possible. Unlike theories, facts such as gravity AND evolution are not subject to falsifying and revising. Perfect!

  6. Guy Randazzo says:

    I think everybody knows it’s more than just “natural selection”. Generations change dramatically over time as mutations in DNA occur. What is not well explained by science or anybody else (and certainly not religion!) is first, how life began in the first place and second – how the mutations over time get so “lucky”. Look at life on this great planet. Thousands of life forms develop nearly perfectly. Is this all by natural selection/lucky DNA mutations? This is the part that I cannot explain and saying that we just keep getting “lucky” with random mutations is something I can’t wrap my head around. There is a lot about nature and evolution that we still don’t understand and I suspect we wont’ during my lifetime.

    • Cornelius Heyer says:

      But that’s an easy one. But first, you have to clear your mind of those categories us humans have made up. There is no “luck” involved, just as there are no “perfect” life forms. Everything that happens just happens, there is no goal (“telos”) to evolution. Now with that in mind, here’s how incremental change goes:

      Every generation consists of NOTHING BUT mutants. It’s not that there occurs one lucky mutation that makes one individual cat run faster, and that individual then has lots of kids. No, every generation always has the full gamut, from the paralyzed to the really fast. This is because small errors during reproduction are inevitable, so no individual is an exact clone. This has nothing to do with luck.

      Now what happens is that outer circumstances see to it that the weak die early with no chance to procreate, while, on the other side of the spectrum, the fastest individuals have successful lives and many kids. So the next generation of individuals will be carrying the genes of those faster animals. This has nothing to do with luck.

      For an outside observer, this may seem, in hindsight, like a purposeful development resulting in the cheetah. But the fact that cheetahs exist is pure chance, it’s a random impression of one momentary state of the evolutionary process. Cheetahs will soon be gone again, they’re not “perfect”, but just one through station for evolution, like all other species.

      tl;dr: Genetic mutation means that every generation offers a plethora of variations on the same species, from the outset. External circumstances then choose which variation prevails. That’s not luck, that’s just something that happens.

    • That’s not even 10 minutes well spent!

  7. Charles R Meyer says:

    What’s especially curious is that no one questions the science of selective breeding. This past weekend they ran the Kentucky Derby, and no one challenges the idea that thoroughbreds are sired with an eye to the skill sets of the stallions and meres they come from. The standard comeback, of course, is that breeding alone can never result in a new species. This is largely a reflection of two blind spots that disrupt our thinking in this arena: a failure to appreciate that relatively minor variations may distinguish one species from another (most people think only it terms of widely divergent categories), and our inability to grasp changes over geologic time frames and thousands of generations of adaptive selection.

  8. Nigel says:

    In a dynamic universe/environment, Evolution is also implicit in the tautology; “whatever exists is adapted to exist”.

  9. Guy Randazzo says:

    Nigel – I think that is what I ponder more than anything else “whatever exists is adapted to exist”. What is the “Force” that keeps life moving forward and adapting? Just ignore the greater universe and just focus on the evolution of life on our little Earth. What force drives the DNA mutations to be so eloquent? Religious folks will say “God” designs everything. I realize that life evolves very, very slowly and the changes in species and new species evolve very slow over time. But in the end, what we see today, are thousands and thousands of near perfect life forms. I don’t think we have a good explanation of how life and the DNA mutations always seem to get it “right”, with life forms that are beyond belief. I’m ready to accept that it’s just “luck” and evolution as we have defined it. Not any more than I accept that God did it all. 🙂 There is something we don’t understand that keeps me wondering and wondering and wondering…..

    • Andreas Schiller says:

      Life and DNA mutations do not always get it right. On the contrary!

      (Speaking with Dawkins:) However, organisms that die young or fail to copulate never become ancestors. They are always removed from the gene pool. That’s why every single living organism on this planet is standing at the end of an unbroken line of winners in this brutal struggle for survival and reproduction.

      Blind randomness and a merciless natural world is all it takes to create this wonderful variety of lifeforms we can observe today.

      No place for god to creep in.

    • Cornelius Heyer says:

      ” I don’t think we have a good explanation of how life and the DNA mutations always seem to get it “right”, with life forms that are beyond belief.”

      “There is something we don’t understand that keeps me wondering and wondering and wondering…..”

      This is actually the very thing evolution is explaining, and I tried to explain it in response to your other post (see above). The key is that there is no “big picture” for evolution. There’s just billions and billions of mutations and resulting individuals and successful or unsuccessful lives.

      If you’re thinking about “getting mutations just right” or “life forms beyond belief [fascinating for us!]”, then you apply human categories to natural chaos. You see the end product and try to make sense of why evolution led up to this. But that’s not the right angle. Evolution is just something that constantly happens and happens and happens. What you see today is just a random, completely insignificant glimpse. All that you have to look at is how the incremental change in one generation comes about, and you understand it all.

  10. Andreas Schiller says:

    Evolution is a fact – first of all. It occurs in our natural world. It can be observed and studied. It’s an inherent property of our world. It’s so stunningly trivial and obvious that we humans didn’t grasp it until just a few generations ago: Things that don’t die easily do (surprise!) live longer!

    The theory of evolution is “just” our best explanation how evolution actually takes place.

    Evolution is both – a fact and a theory. This is key for understanding that evolution is not “just a theory”.

  11. Robert Tannenbaum says:

    I am a retired elementary school teacher. Every year, on the day of “open school night,” I would teach the lesson:
    What is a Myth?
    Definition: A myth is a story made up to explain natural events that were unexplainable by the science of the time.
    Example: Every day, Apollo, the sun god of ancient Greece, rode across the sky in his gleaming golden chariot. When he finished his ride across the sky, he put his horses in their stable and that was night to the Greeks. etc.
    I left the lesson on the blackboard so that when the parents came into my room in the evening, they could read the lesson if they were observant enough.
    Why did I do that?
    Well the answer is complicated. I was looking for a parent who asked these questions:

    “Aren’t all religions like Greek Mythology? Aren’t they just stories made up to explain stuff the people of the time didn’t understand? Wasn’t fear the motivational factor for making up these stories?”

    No one asked that question. I had to find my future friends elsewhere.

    Now I have to find some one who agrees with the statement:

    There is no such thing as race. We are all African.

    It is amazing to me that people think I am crazy. When surveyors ask me my race, I tell them none. Just write none. Race is a myth.
    Sometimes I am also convinced that we lived on the beaches of the World during “heat ages” because of the hydrodynamic hair on our bodies, (runs toward feet when wet) and the length of our hair if we didn’t cut it. What other primate has such long hair? (The babies who had mothers with longer hair where able to grab on when the powerful waves came.)

    • Nigel Morris says:

      Robert, you are not crazy – we are indeed all Africans. The variation in DNA between the most apparently diverse human beings (skin colour; bone structure) is much less than in most other animal species. And the difference in DNA between some African negroes within Africa is greater than the difference between negroes and caucasians – i.e. whites are more closely related to some blacks than blacks are to other blacks. The Supreme Court in Brazil on one occasion was unable to rule on a legal point involving race because it said it was unable to determine what race is.

      Am not so sure about your “hydrodynamic hair” hypothesis though…

  12. Robert Tannenbaum says:

    When I ask people what emotion they feel when they are “cut off” by another driver while doing 70 mph. on the highway, I always get the same answer:
    “That’s easy. I get roaring mad, angry!”
    And of course, yes, they get angry, but that is a secondary emotion. It is the child of another stronger emotion, FEAR. “I almost got killed or seriously hurt by that #$%^%$$.”
    I sometimes explain that my theory of road rage is that a person has a problem with acknowledging the fact that they had immense fear when the incident happened. Macho men do not have fear. They have anger! Anger is manly!
    Religion grows out of fear. When the snows came and the plants and animals died, early caveman became seriously scared of dying. No food can scare the crap out of you. So you make up stories about the sun and the earth having an fight, and the sun deciding to leave. So the earth becomes a woman, and the sun a man.
    Solution: Heat the earth up by burning trees to show the sun she is “hot” for him again. It works. Spring comes and the plants and animals return. Magic. Christmas trees evolve out of the large burnings…Religion grows. Beliefs grow. Fear begets belief.
    Facts have a hard time when it comes to changing beliefs. Fear is stronger than facts.
    There is no evolution. There is no global warming, etc. Fear wins out. We have a reptilian brain that responds very well to fear. Survival uber alles.

  13. Susan Campbell says:

    Robert, I love the idea of leaving your lesson “What is a myth” up on the board for the parents coming to the “open school night” to read and reflect upon; disappointing that no-one made the connection to other religious stories.
    I fight the good fight by telling my grandchildren that we have always told ourselves stories that explain or comfort, hence the “stories” which have become religions.

  14. Antonio B. Nafarrate says:

    I think that Evolution should be referred as “the Principle of Evolution” since is well accepted by the majority of scientists and the better educated people. At least the less informed will not reply “it is only a theory”.

  15. Kofi Ahubley says:

    One thing that makes me a lover of the Scientific approach to explaining creation is that all theories are still TENTATIVE. Can same be said for religion?

    I think it’s clear beyond doubt that there is nothing like ‘just a theory’ but rather may be ‘just a hypothessis/conjecture.’

  16. Juan Valera says:

    Sometimes, people saying that “Evolution is just a Theory” are genuinely confused about the difference between “scientific theory” and “Sherlock Holmes Hypothesis”.
    But in those cases where it’s said just as a lazy way to disprove science I like to answer: “Yes, we can play to say tautologies indeed, evolution is a theory, science is science, and god is an imaginary friend”.
    I know, it isn’t nice, but sometimes it just feels right.

  17. Ejnar J. Fjerdingstad says:

    When I hear the hoary old “It’s just a theory!” comment, I say, “Yes, it is a theory, confirmed by an enormous number of observations, as are gravity or relativity. Religion, however, is just a postulate, unsupported by any observation. Moreover, there are a large number of such postulates, often mutually incompatible. Thus they cannot all be right, but nothing prevents them from being all wrong!

  18. Maybe the best way to put it is: Yeah, evolution is just a theory based on hard verifiable facts; you got any better theories based on hard verifiable facts?

  19. Coiquaud Jean Pierre says:

    ANAXIMANDER, Ionian philosopher (610 to 546 before Christ) noticed that the new-born humans are defenseless and unable to survive on their own.

    He concluded that the first human on earth could not have survived as a human baby.
    As an hypothesis, he supposed that humans have evolved from animals which had more robust/autonomous kitten.

    Anaximander thought that the existence of marine fossils found on land had some logical implications. He mentioned several times that fishes were possibly the first animals able to adapt and live outside oceans.

    Therefore, this pre-scientific approach of the necessary existence of an EVOLUTION “process” (improperly called “theory”) goes back 2.500 years before Darwin.

  20. Joe Maddox says:

    There is a fundamental harm to the core of Christian salvation proposed by the biological fact of evolution.
    The biological fact of evolution makes Adam a fiction, thus, sin entering the world through Adam a fiction as well, and Jesus dying to atone for that sin becomes pointless.
    Many Christian believers who rant against the biological fact of evolution may not realize how destructive it is to their salvation faith–but emotionally refuse to admit evolution is a fact to protect their faith, which is rooted in emotion, not knowledge.
    The fact of evolution threatens not only their faith but their alleged eternal life. It makes no difference there is no evidence of a human afterlife they believe it threatened.
    The irrational rejection of the biological fact of evolution is not about to go away soon.

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