These days, biologists believe all living things come from other living things. But for a long time, people believed that life would, from time to time, spontaneously pop into existence more often—and not just that one time at the base of the evolutionary tree. Even the likes of Aristotle believed in the “spontaneous generation” of life, until Louis Pasteur debunked the theory—or so the story goes. 

In a famous set of experiments, Pasteur showed that when you take a broth, boil it to kill all the microscopic organisms floating inside, and don’t let any dust get in, it stays dead. No life will spontaneously emerge. 

His experiments have been considered a win for science—but according to historian James Strick, they might have actually been a win for religion. 

This episode originally aired on Science Friday, when Elah joined Ira Flatow and science historian, James Strick, to find out what scientists of Pasteur’s day really thought of his experiment, the role the Catholic church played in shutting down “spontaneous generation,” and why even Darwin did his best to dodge the topic.

Though Darwin was bold enough to go public with his theory of evolution, he seemed to shy away from the spontaneous generation debate. But his theory inevitably invited the question: if life could spontaneously arise once on Earth, why not many times? James Strick writes about Darwin’s complicated relationship with spontaneous generation.

The basic premise of Louis Pasteur’s famous swan-necked flask experiment is shown below. The swan necks let life-nourishing air into the flask, but kept potentially contaminating dust out.

Louis Pasteur's spontaneous generation experiment illustrates the fact that the spoilage of liquid was caused by particles in the air rather than the air itself. These experiments were important piece

James Strick, associate professor at Franklin and Marshall College

This episode of Undiscovered was produced by Elah Feder and Alexa Lim. Our theme music is by I Am Robot And Proud. 

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