Opponents of well-established scientific ideas (like evolution or climate change) often have to resort to the same playbook. If you can’t produce scientific evidence to support your position, your options are pretty limited. Opponents commonly feel that if they can just show that there are problems with the consensus explanation, their preferred explanation will come out on top by default. They can wade into the details and point to remaining unknowns, questions for which there are still several competing answers, or topics for which their limited understanding leads them to think they’ve discovered an error.
This seems to be motivated by, or at least accompany, a mental model of the scientific consensus as a house of cards. All you need to do is dislodge one of the cards (supporting pieces of evidence) and the entire structure will come tumbling down. I think this sometimes results from conspiratorial thinking. If the scientists who are part of the consensus cabal have falsified their work and lied to preserve the Great Lie, then surely the clues will take you to the proof that dispels the sham. And if you think of the consensus idea as some a priori position that the scientists have merely gathered evidence to defend, you might think of the science as a vulnerable construct put together to prop up the consensus. All you need to do is discover what inconvenient evidence was left out in the interest of structural integrity.
Obviously, this mental model fundamentally misunderstands the nature of science. Instead of viewing the evidence as intentionally constructed because of an idea, it should be (mostly) understood as a haphazard collection that just so happens to result in the consensus. Perhaps it’s better to imagine piles of rocks.
Suppose (hang with me here) that we are sorting rocks on the basis of color. Black basalt, red granite, green schist, and white-gray dolomite. Collection sites for each are set up several miles from each other. Epic excavation projects on going on nearby, so there’s no end to the rock supply. Every time a truckload of rocks comes in, they are sorted by color and sent to their respective collection sites, where they are tossed onto growing piles. Some rocks are hand-sized, others are boulders as large as a car. No worries- our machinery is quite good.
Now suppose we fast-forward a few decades. As it turns out, the red granite and white-gray dolomite piles are fairly meager. The pile of green schist has grown to an impressive height of a little over three hundred meters. But the black basalt pile is a mind-bending 3200 meters tall, visibly breaking clear above the horizon for miles and miles around. (Incoming truckloads are now air-lifted to the peak by workers who have taken their initial directives very seriously.) It is, in fact, so tall that its peak now pushes above the snowline, leaving its crown dusted with white powder.
But now, a stern looking man with a brimmed hat and neat beard has arrived at the gate. He has long maintained that the bedrock in the area is almost entirely green schist, and suspects that the rock sorters have been dishonest. Convinced that no pile of basaltic rocks could ever be so large as to be snow-capped, he has come to investigate.
The workers, some chuckling and some disquieted by the man’s dour appearance, step aside as he approaches. He walks up to the base of the pile and squints his eyes as he inspects the rocks nearby. Seeing nothing but beautiful black basalt, he begins to slowly stalk the skirt of the mountain. Eventually, he nearly squeals with excitement and scrambles ten feet up the pile before nearly tumbling back down, returning with a rock clenched in his hand. It’s a dark green schist, out of place. He turns to the workers and hoists it aloft, his face beaming with triumph. A foreman shrugs, takes it from his hand, and tosses it into a nearby truck before signalling the other employees to get back to work.
The strange man spends every day for the next week scouring the mountain for rocks that don’t belong. He finds three. Removing his hat to wipe the sweat from his head, he gazes bitterly at the bright, white peak that taunts him. Exhausted, he drives home, slowing as he passes the pile of green schist. It hasn’t grown.
Clearly, the piles in this ridiculous allegory are accumulated evidence. The snowline could be the threshold of scientific consensus. If you are successful in removing a piece of supporting evidence, even if it’s a large one, the rest remain. Unless, through the slow-hard work of research, a different idea rivals the accumulated evidence of the first, little has changed. There is no “keystone” in the rock pile, without which everything comes tumbling down.
Obvious as this seems, we really do tend to think that way. As John Kenneth Galbraith put it, “Faced with the choice between changing one’s mind and proving that there is no need to do so, almost everyone gets busy on the proof.” Motivated reasoning loves easy explanations for the error of our opposition’s ways. (Uh-oh… Spot any here?) Few easy explanations are more tempting than going for a sweep of the leg we imagine them to stand on- the faulty assumption that makes the details of their evidence irrelevant.
Because of this, I think that the “teach the controversy” bills circulating in state legislatures are nearly as effective as explicitly teaching intelligent design in classrooms. In order to teach “alternatives” to something like evolution, you can’t rely on marshaled evidence. You have to propose that other ideas (like intelligent design) stand on equal footing, and it’s all a matter of how you interpret the evidence. That is, the key assumptions change everything. To validate that point of view in a science classroom is to give students all the tools they need to ignore the snow-capped mountains of evidence. It wouldn’t be so tall if it weren’t for that Jack of Spades…