Excursus: Hypotheses, Theories, and Squirrels
I was going to break the flow of posts to address a theological issue which I thought germane to the series on the Fall that I’ve been running. Then a comment on my last post struck me as worthy of an entire post, rather than a combox reply. It touches on science and the scientific method, and (as a sometime science teacher) I think it’s always good to make use of opportunities to discuss misconceptions about how they work.
In the original post, remarking on the things we know for certain (or as certain as we can know) regarding the origin of the world and humanity, I said the following:
3. Humans, beyond any shadow of a reasonable doubt, evolved from other hominids; any other account must be considered metaphorical, whether it be the molding of man from the soil in Genesis or the creation of man by a committee of demons in The Secret Book of John.
In commenting on this post, commenter Christopher C. Randolph says, with my emphasis added:
#3 can be jettisoned, I think. It’s a cool theory but hasn’t been proven. I don’t think it can be proved. Nor can God creating humans and everything else be scientifically proved either. The most that can be legitimately concluded is that the fossil record suggests…. it’s unscientific to say that evolution is a fact, I think.
Which isn’t to say that I don’t think it should be taught in science class. But it should keep to its “theory” status.
The rest is great! But I thought that the accepted age of the earth was 10,000,000 years?
First, on a smaller note, the age of the Earth is estimated at about 4.54 billion (4,540,000,000) years old. This is based on studies of the half-lives of various radioactive substances; a good, non-technical discussion of this is here. To the more significant issue: I think that the issue here is a misunderstanding of what “theory” means when used by scientists, and how the scientific method works. Such misunderstanding is extremely common, so I think it is good to address it. Rather than spouting definitions, let me tell a true story that I hope will illustrate what I want to get across.
A month or so ago I was sitting in the living room with my nine-year-old daughter when we heard a thumping sound against the wall. She asked me, “What was that, Daddy?” I answered, “Probably the wind blowing a tree branch against the wall.”
This was a hypothesis. A hypothesis is commonly defined as an “educated guess”. A guess, because that’s what it is–certainly not proven. “Educated”, though, because it’s not a random guess. My hypothesis that it was the wind was based on having heard and at the same time seen tree branches hit the wall before; on my knowledge of our house and neighborhood; and so on. A truly random guess, such as “It’s someone climbing up the side of the house,” or “Alien spaceships caused it!” would not be worthy of consideration (unless I actually saw the climber or the aliens!) and would be a waste of time. When you make a hypothesis you try to use what you do know to make a reasonable guess about what you don’t.
Still, a hypothesis is nevertheless a guess.
Over the next few weeks I’d periodically hear that sound again. On some such occasions I noted that it was not, in fact, windy at all. Thus, my original hypothesis did not stand up to new data and observations. I also began hearing a scrabbling sound as if some animal was in the rafters, often right after the thumping sound. Now I made a new hypothesis–there must be birds in the eaves. We’ve had them in the eaves on the back of the house, and I know what they sound like. The sound I was hearing now wasn’t quite the same, but it was similar, so “birds in the rafters” was my new educated guess.
About a week ago, my wife mentioned, in passing, the squirrels in the ceiling. I said, “What?” She explained that she’d seen a couple of squirrels jumping back and forth from one of the trees in the front yard (a tree that has long been a squirrel magnet, I might point out) to the roof and back. Moreover, she kept seeing them vanish into the guttering, from which they’d go into the eaves. The side of the house on which they could jump to the roof from the tree, by the way, is the exact place from which the various sounds had been issuing.
Finally, a couple days ago, I was sitting on the front steps as my daughter was playing in the front yard when I noticed a squirrel emerge from the gutter and jump from the roof to the tree. Mystery solved!
“Squirrels live in my eaves” was now my theory regarding the sounds. Notice that at this point it’s not a matter of guesses. I have made many observations of various different types: thumps, scrabbling sounds behind the ceiling, and squirrels jumping from tree to roof and roof to tree at the point the noises came from, and squirrels actually seen going into the eaves.
In short, a theory is a model which explains a large number of various observations of different kinds over time and which is capable of making predictions which can be verified by further observations.
It is a model, not just a guess (not even an educated guess): the theory that squirrels lived in our eaves was a broad picture of what was going on, not just an individual observation (“I heard a thump”).
It explains a large number of various observations of different kinds: The squirrel theory explained thumps, scrabbling noises in the ceiling, squirrels observed jumping to and from the roof, and squirrels observed jumping into the guttering and the eaves.
The theory stands up over time as more observations are made: It took me over a month to come to the conclusion as to what was happening.
The theory can make predictions which can be verified by further observations: Based on the squirrel theory, I can predict that I will see squirrels continuing to jump on the roof; that I will continue to hear scrabbling sounds; that I will see cats frequently in our front yard hoping to catch a squirrel (there are many cats in our neighborhood); and that I will find a plentiful food source that attracts the squirrels in the first place. I have, in fact, observed all of these things (the tree’s a maple and the squirrels seem to like the little “helicopter” seeds).
See how very much different the squirrel theory is from my off-the-cuff wind hypothesis.
OK, “proof”. When people think of scientists “proving” something, they tend to think of a mathematical or geometric proof, or of a detective presenting some dramatic piece of clinching evidence (“See how the prints on the weapon exactly match the defendant’s prints, and how he is left-handed and the shot was consistent with being fired by a left-handed person!”) It doesn’t work that way, alas.
In fact, a theory can’t really be proved at all. This is not, however, because it’s weak or missing evidence; it’s actually the opposite. It’s so strong that it can’t be proved. Another way to put it is to say that it’s impossible to prove a theory but that it can always be disproved.
Short of posting watch, placing miniature video cams under my eaves and on the roof, putting motion sensors out, etc., I can’t know that every single instance of thumps is caused by squirrels. Sometimes it probably really is the wind. For that matter, to give a ridiculous example, it’s possible that the squirrels are actually tiny, squirrel-shaped robots that some sinister agency is using to gather data on me. Unless I catch one and dissect it (ugh!) I won’t know for sure….
That’s a weird extreme, but it’s a good example of the way that a sufficiently paranoid or demented person could always propose some non-squirrel explanation that could hypothetically be true but almost certainly isn’t. There’s no possible way I could disprove every conceivable alternate hypothesis, since I lack infinite time, resources, and knowledge. However, I don’t have to do so. The theory fits the observations, and no observations have occurred that would call it into question (such as seeing a cat jump from the tree to the roof and make the same thumping sound I’ve heard before).
Take another example. It is our operating theory that the world exists as we see it to be. Now it’s conceivable that we’re all actually hooked up to the Matrix, and all of our observations throughout our entire lives are mistaken. However, that’s an awful lot of observations over an awful long period of time and the theory that the world as we know it is real does an awfully good job of explaining all the observations. Thus, I’m going to want to see an awfully good refutation of the theory–like Morpheus giving me the red pill and immediately waking up with him pulling me loose from the pod I’m hooked to!
Thus, while theories cannot be proven as such, the very fact that they are considered “theories” in the scientific sense means that they have stood the test of time in thousands of observations, experiments, and tests. Thus a theory–such as atomic theory, the Theory of Relativity, or, yes, the evolution of humans and other animals from other species–is never “just” a theory (“theory” in this usage really means “hypothesis”). It may not be absolute truth (which we humans probably can never attain, anyway), but it’s about as close to “fact” as you can reasonably get.
Now it’s important to note two things. First, humans are limited in what we know, in what we can know, and in the observations we can make. Thus no theory is likely to explain every possible phenomenon. As I said before, just because we’ve got squirrels in the eaves it doesn’t mean the wind won’t occasionally blow the tree branches up against the house. For that matter, thumps might occasionally occur for reasons I can’t figure out–house settling, other animals, whatever.
Second, any theory (including that the exterior world is real and not the Matrix) can always be disproved; but the evidence provided to disprove it must be strong, compelling, and must come from the one making the claim (after all, if you tell me you’re Morpheus and that the room we’re in is not real, it’s not up to me to prove it is real, but you to prove it’s not by handing me a red pill!). The geocentric theory, for example–that the Earth was stationary and circled by the planets and Sun and moon–worked quite well for centuries. In the Renaissance, however, observations of the Moon’s angular momentum and Galileo’s famous observations with his telescope provided overwhelming evidence that the geocentric model was untenable. After initial opposition (we all know about Galileo…) the heliocentric theory–that the Earth, Moon, and planets orbit the sun–won the day, and is still held today.
To bring it all home: No professional biologist, no matter what his religious or philosophical beliefs, doubts evolution in general, or the evolution of humanity in particular. There are massive amounts of data from biology, genetics, anthropology, archaeology, geology, physics, chemistry and so on which all confirm evolutionary theory. It is not a hypothesis, not “just” a theory, but about as close to fact as can reasonably be attained. Francis Collins is a conservative, Evangelical Christian, but has strongly defended evolution, most notably in his excellent book The Language of God. Kenneth Miller, a practicing Catholic has also defended evolution in Finding Darwin’s God, another excellent book. Even Micheal Behe, a proponent of so-called intelligent design (which I have problems with, but that’s another can of worms for another day) acknowledges the vast age of the Earth and that chimps and humans have common ancestry.
Other good books explaining evolution are Why Evolution is True, by Jerry Coyne (he’s an atheist, so I disagree with him there, but his explanations of evolution are quite good) and Your Inner Fish, by Neil Shubin.
Therefore, at the end of this unusually long post, I stand by my original statement that we “beyond any shadow of a reasonable doubt” evolved from earlier hominids, who evolved from earlier mammals, who evolved from reptiles, and so on. Anyone is free to disagree with this (though I’d say they’re wrong to do so!); but I hope I’ve contributed a little to explaining just how science work and to clearing up the misconception about what theories actually are.
So in the next post we move from science to theology–prepare to shift gears!
Part of the series Legends of the Fall.