Is the Science Ever Settled? Theories, Hypotheses, and What Science Really Does


Any time you write an article talking about the limits of science, as I did in my recent “The Importance of Not Being Certain,” someone will invariably show up to say “evolution is just a theory.” This pretty much always means the person saying it doesn’t have a very good grasp of either “evolution” or what a “theory” is, and so I thought, “okay, that’s a column.”

Let’s look into Darwin’s theory of the origin of species, and in the process let’s look at how science works to build confidence in something that is “just a theory.”

Here’s what Darwin actually said: species originate through natural selection among different characteristics.

He didn’t have access to the nearly 160 years of research that followed. He just made an argument from his observations at the time. Ernst Meyer (this is cribbed from Wikipedia) summarized Darwin’s argument as follows:

  • Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).
  • Despite periodic fluctuations, populations remain roughly the same size (fact).
  • Resources such as food are limited and are relatively stable over time (fact).
  • A struggle for survival ensues (inference).
  • Individuals in a population vary significantly from one another (fact).
  • Much of this variation is heritable (fact).
  • Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (inference).
  • This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).

Two things to notice here: first of all, this is a theory: “a supposition or a system of ideas intended to explain something.”

This theory takes the form of an argument: “a sequence of logically connected assertions that lead to a conclusion.”

Some of them are well-established, so Meyer called them “facts,” and some are called “inferences,” which is to say they’re conclusions drawn from the observations before them.

We’ll come back to that in a second, but I want to point out something else: at no point does Darwin make an argument for where life “came from,” how what we call life originated. So everyone winding up to throw “but evolution doesn’t explain the origin of life” at me, just stop. Darwin and evolutionary theory don’t explain that, because it’s not their job.

Those inferences are the key. Every one of those steps should be examined closely, but the ones labeled as “fact” are pretty non-controversial.

Now we’re coming to the way science is actually done. There is a whole topic of the “philosophy of science” and lots of people making their livings writing about what science is and does, but for actual working scientists there are some pretty common guidelines.

A very influential paper on how to learn to do science is John Platt’s paper “Strong Inference.” While it’s controversial among philosophers of science, it’s not primarily a philosophy paper, it’s a “How To” paper.

Before we talk about strong inference, though, we need to take a side trip for some terminology. A hypothesis for which there exists a conceivable experiment that could prove it wrong is falsifiable. Performing that experiment, if successful, is a falsification. So, if my hypothesis is “Coffee is instantly fatal” it’s falsifiable, because you can drink coffee and if you don’t die, it’s not true. So I take a drink of coffee … yep, I’m still here, and so I’ve falsified the hypothesis.

So, Pratt recommends a process that goes basically like this:

1. You observe something.

2. You make several hypotheses. In this case, a hypothesis means a statement about the observation that proposes an experiment that would show the hypothesis is wrong -- in other words, it’s falsifiable.

3. You perform the experiments. Every hypothesis that is actually falsified, you discard.

4. With what you’ve learned, you go back to 1 and repeat.

When you’re down to just one hypothesis, or at least when you’ve excluded some hypotheses, you’ve got a result, which you publish in a form that lets other people replicate your experiment and verify your results. Then what do you do? Remembering that science is never settled, you or someone else goes back and does it again.

Think about what happens over time. As this process goes on, you accumulate more and more explanations for some original set of observations that you’ve attempted to falsify, but haven’t been able to falsify. The more of those you have, the greater your confidence that you’ve got at least a good partial explanation.

Now, let’s look at those inferences that are the more controversial parts of the argument.