Being Wrong - Kathryn Schulz [64]
Two of my favorite examples of this form of confirmation bias come from the wonderfully evidence-resistant realm of early anatomy and physiology. The first is the traditional Judeo-Christian belief that women had one more rib than men (Adam having furnished one for the making of Eve). This belief somehow survived until 1543, when the Flemish anatomist Andreas Vesalius finally showed otherwise—by, you know, counting. The second includes just about every claim ever made by Pliny the Elder, a Roman scientist and author who lived in the first century AD. Pliny was, arguably, the most influential misinformed man in history, a veritable Johnny Apple-seed of bad ideas. Consider his thoughts on menstruation, as recorded in his supposed masterpiece, the scientific omnibus Naturalis Historia:
On the approach of a woman in this state, milk will become sour, seeds which are touched by her become sterile, grafts wither away, garden plants are parched up, and the fruit will fall from the tree beneath which she sits. Her very look, even, will dim the brightness of mirrors, blunt the edge of steel, and take away the polish from ivory. A swarm of bees, if looked upon by her, will die immediately;…while dogs which may have tasted of the matter so discharged are seized with madness, and their bite is venomous and incurable.
Surely it wouldn’t have been hard to run a quick experiment on that one. And yet, until the stirrings of the Scientific Revolution, no one thought to go looking for evidence that might contradict the prevailing medical beliefs of 1,500 years.
As perverse as they may seem, these many forms of creatively dodging the counterevidence represent a backhanded tribute to its importance. However much we ignore, deny, distort, or misconstrue it, evidence continues to matter to us, enormously. In fact, we ignore, deny, distort, and misconstrue evidence because it matters to us. We know that it is the coin of the epistemological realm: that if we expect our beliefs to seem credible, we will have to furnish their grounds. In a sense, this is the positive side of the ’Cuz It’s True Constraint. If we think we hold our beliefs because they comport with the evidence, we must also think that we will revise them when new evidence arises. As a consequence, every proposition, no matter how much we might initially resist it, must have an evidentiary threshold somewhere, a line beyond which disbelief passes over into belief. If you show up on my doorstep with a spaceship and a small green friend and we all fly off to Pluto together, I will commence believing in UFOs. Closer to home, we see evidentiary thresholds being crossed all the time. That’s how belief in geocentrism—once the most radical of conjectures—came to be taken for granted, and how a global consensus is emerging on climate change, and how Elizabeth O’Donovan eventually accepted that Orion is a winter constellation.
But we also see evidentiary thresholds not being crossed—sometimes for centuries, as in the case of Pliny’s medical theories. As powerful as confirmation bias is, it cannot fully account for this: for the persistence and duration with which we sometimes fail to accept evidence that could alter our theories. Another factor is the claim, implicit or explicit in many belief systems, that attending to counterevidence can be dangerous—to your health or family or nation, to your moral fiber or your mortal soul. (As a European Communist once said in response to the question of whether he had read any of the criticisms of Communism, “A man does not sip a