M Semmelweis reflex.

The work of Ignaz Semmelweis, a nineteenth-century Hungarian doctor, met a similar fate. He worked at a teaching hospital where doctors routinely handled cadavers and also delivered babies, without appropriately washing their hands in between. The death rate of mothers who gave birth in this part of the hospital was about 10 percent! In another part of the same hospital, where babies were mostly delivered by midwives who did not routinely handle cadavers, the comparable death rate was 4 percent. Semmelweis obsessed about this difference, painstakingly eliminating all variables until he was left with just one: doctors versus midwives. After studying doctor behavior, he concluded that it must be due to their handling of the cadavers and instituted a practice of washing hands with a solution of chlorinated lime. The death rate immediately dropped to match that in the other part of the hospital. Despite the clear drop in the death rate, his theories were completely rejected by the medical community at large. In part, doctors were offended by the idea that they were killing their patients. Others were so hung up on the perceived deficiencies of Semmelweis’s theoretical explanation that they ignored the empirical evidence that the handwashing was improving mortality. After struggling to get his ideas adopted, Semmelweis went crazy, was admitted to an asylum, and died at the age of forty-seven. It took another twenty years after his death for his ideas about antiseptics to start to take hold, following Louis Pasteur’s unquestionable confirmation of germ theory. Like Wegener, Semmelweis didn’t fully understand the scientific mechanism that underpinned his theory and crafted an initial explanation that turned out to be somewhat incorrect. However, they both noticed obvious and important empirical truths that should have been investigated by other scientists but were reflexively rejected by these scientists because the suggested explanations were not in line with the conventional thinking of the time. Today, this is known as a Semmelweis reflex.

Individuals still hang on to old theories in the face of seemingly overwhelming evidence—it happens all the time in science and in life in general. The human tendency to gather and interpret new information in a biased way to confirm preexisting beliefs is called confirmation bias.