Proof And Disproof Proof

Scientists don't usually talk about proving themselves right, because proof suggests certainty (remember Ashley Montagu's truth without certainty!). The testing of explanations is in reality a lot messier than the simplistic descriptions given previously. One can rarely be sure that all the possible factors that might explain why a test produced a positive result have been considered. In the guppy case, for example, let's say that you found two habitats that differed in the number of predators but were the same in terms of amount of food, water temperature, and number and type of hiding places—you tried to hold constant as many factors as you could think of. If you find that guppies are less colorful in the high-predation environment, you might think you have made the link, but some other scientist may come along and discover that your two environments differ in water turbidity. If turbidity affects predation—or the ability of female guppies to select the more colorful males—this scientist can claim that you were premature to conclude that color is associated with predation. In science we rarely claim to prove a theory—but positive results allow us to claim that we are likely to be on the right track. And then you or some other scientist can go out and test some more. Eventually we may achieve a consensus about guppy color being related to predation, but we wouldn't conclude this after one or a few tests. This back-and-forth testing of explanations provides a reliable understanding of nature, but the procedure is neither formulaic nor especially tidy over the short run. Sometimes it's a matter of two steps forward, a step to the side (maybe down a blind alley), half a step back—but gradually the procedure, and with it human knowledge, lurches forward, leaving us with a clearer knowledge of the natural world and how it works.

In addition, most tests of anything other than the most trivial of scientific claims result not in slam-dunk, now-I've-nailed-it, put-it-on-the-T-shirt conclusions, but rather in more or less tentative statements: a statement is weakly, moderately, or strongly supported, depending on the quality and completeness of the test. Scientific claims become accepted or rejected depending on how confident the scientific community is about whether the experimental results could have occurred that way just by chance—which is why statistical analysis is such an important part of most scientific tests. Animal behaviorists note that some social species share care of their offspring. Does this make a difference in the survival of the young? Some female African silver-backed jackals, for example, don't breed in a given season but help to feed and guard the offspring of a breeding adult. If the helper phenomenon is directly related to pup survival, then more pups should survive in families with a helper.

One study tested this claim by comparing the reproductive success of jackal packs with and without helpers, and found that for every extra helper a mother jackal had, she successfully raised one extra pup per litter over the average survival rate (Hrdy 2001). These results might encourage you to accept the claim that helpers contribute to the survival of young, but only one test on one population is not going to be convincing. Other tests on other groups of jackals would have to be conducted to confirm the results, and to be able to generalize to other species the principle that reproductive success is improved by having a helper would require conducting tests on other social species. Such studies in fact have been performed across a wide range of birds and mammals, and a consensus is emerging about the basic idea of helpers increasing survivability of the young. But there are many remaining questions, such as whether a genetic relationship always exists between the helper and either the offspring or the helped mother.

Science is quintessentially an open-ended procedure in which ideas are constantly tested and rejected or modified. Dogma—an idea held by belief or faith—is anathema to science. A friend of mine once was asked to explain how he ended up a scientist. His tongue-in-cheek answer illustrates rather nicely the nondogmatic nature of science: "As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life—so I became a scientist. This is like becoming an archbishop so you can meet girls" (Cartmill 1988: 452).

In principle, all scientific ideas may change, though in reality there are some scientific claims that are held with confidence, even if details may be modified. The physicist James Trefil (1978) suggested that scientific claims can be conceived of as arranged in a series of three concentric circles (see Figure 1.1). In the center circle are the core ideas of science: the theories and facts in which we have great confidence because they work so well to explain nature. Heliocentrism, gravitation, atomic theory, and evolution are examples. The next concentric circle outward is the frontier area of science, where research and debate are actively taking place on new theories or modifications and additions to core theories. Clearly no one is arguing with the basic principle of heliocentrism, but on the frontier, planetary astronomers still are learning things and testing ideas about the solar system. That matter is composed of atoms is not being challenged, but the discoveries of quantum physics are adding to and modifying atomic theory.

Figure 1.1

Scientific concepts and theories can be arranged as a set of nested categories with core ideas at the center, frontier ideas surrounding them, and fringe ideas at the edge (after Trefil 1978). Courtesy of Alan Gishlick.

Figure 1.1

Scientific concepts and theories can be arranged as a set of nested categories with core ideas at the center, frontier ideas surrounding them, and fringe ideas at the edge (after Trefil 1978). Courtesy of Alan Gishlick.

The outermost circle is the fringe, a breeding ground for ideas that very few professional scientists are spending time on: unidentified flying objects, telepathy and the like, perpetual motion machines, and so on. Generally the fringe is not a source of new ideas for the frontier, but occasionally (very occasionally!) ideas on the fringe will muster enough support to warrant a closer look and will move into the frontier. They may well be rejected and end up back in the fringe or be discarded completely, but occasionally they may become accepted and perhaps eventually become core ideas of science. That the continents move began as a fringe idea, then it moved to the frontier as data began to accumulate in its favor, and finally it became a core idea of geology when seafloor spreading was discovered and the theory of plate tectonics was developed.

Indeed, we must be prepared to realize that even core ideas may be wrong, and that somewhere, sometime, there may be a set of circumstances that could refute even our most confidently held theory. But for practical purposes, one needn't fall into a slough of despond over the relative tentativeness of scientific explanation. That the theory of gravitation may be modified or supplemented sometime in the future is no reason to give up riding elevators (or, even less advisedly, to jump off the roof). Science gives us reliable, dependable, and workable explanations of the natural world—even if it is good philosophy of science to keep in mind that in principle anything can change.

on the other hand, even if it is usually not possible absolutely to prove a scientific explanation correct—there might always be some set of circumstances or observations somewhere in the universe that would show your explanation wrong—to disprove a scientific explanation is possible. If you hypothesize that it is raining outside, and walk out the door to find the sun is shining and the ground is dry, you have indeed disproved your hypothesis (assuming you are not hallucinating). So disproving an explanation is easier than proving one true, and, in fact, progress in scientific explanation has largely come by rejecting alternative explanations. The ones that haven't been disconfirmed yet are the ones we work with—and some of those we feel very confident about.

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