What had us convinced? And then what did it take to change our minds? A horse comes from horse parents. An amoeba comes from another amoeba that has split in two. And if we work our way all the way back through evolution, all living things come from an original living thing.
They just spontaneously sprang into life. We called it spontaneous generation. You might have learned about this in high school. Science for the win. But it turns out that history is never that simple.
Instead of a win for science, this might have been a win for religion. My guest is here to fill us in on the story behind the story. James Strick is a professor of science technology and society at Franklin and Marshall College in Lancaster, Pennsylvania. Welcome to the show, Jim. So you know the textbook version of spontaneous generation pretty well.
Can you give us the short version of it? But for over 2, years, a lot of very smart people believed in spontaneous generation, going all the way back to Aristotle.
But the Catholic church was very against this idea. Why were they so against it? Saint Augustine, for example, in the early fifth century, one of the most important and influential church fathers who left a lot of writings, had no problem at all reconciling spontaneous generation with Catholic doctrine. He thought that God had put seed principles into certain kinds of matter at the beginning of creation and that meant that, over time, they would unfold and develop into living things.
Church is moving away from Aristotelian physics because of all the new discoveries of the scientific revolution. They work with Genesis in a way, but not in a way that is compatible with spontaneous generation. It conflicts with this doctrine that all generations of organisms were created at the beginning, serially in case, that Russian dolls within the eggs or the sperm of the very first member of that species.
But also, as you get into the early 18th century, spontaneous generation is seen to potentially be an underpinning for philosophical materialism, the idea that matter alone contains everything necessary to generate life, mind, and that things like the soul and the afterlife are an illusion. You can have life coming up from non-life. I could see why they would object to that.
So in the s, you get a showdown between two scientists. You have Louis Pasteur and, somewhat less famous today, Felix Pouchet, over this idea of spontaneous generation. What happened? The French Academy of Sciences, the most prestigious body of scientific opinion in France at the time, responded to this by posing a competition. The Greek philosopher Aristotle — BC was one of the earliest recorded scholars to articulate the theory of spontaneous generation , the notion that life can arise from nonliving matter.
As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water.
This theory persisted into the seventeenth century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding.
Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont , a seventeenth century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.
He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers Figure 1. Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars.
He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation. Figure 1. Maggots only appeared on the meat in the open container. However, maggots were also found on the gauze of the gauze-covered container. In , John Needham — published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes.
After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.
This suggested that microbes were introduced into these flasks from the air. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation Figure 2.
Typically, the idea was that certain forms such as fleas could arise from inanimate matter such as dust or that maggots could arise from dead flesh. A variant idea was that of equivocal generation, in which species such as tapeworms arose from unrelated living organisms, now understood to be their hosts. Doctrines held that these processes were commonplace and regular. Such ideas were in contradiction to that of univocal generation: effectively exclusive reproduction from genetically related parent s , generally of the same species.
The doctrine of spontaneous generation was coherently synthesized by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. Today spontaneous generation is generally accepted to have been decisively dispelled during the 19 th century by the experiments of Louis Pasteur.
He expanded upon the investigations of predecessors, such as Francesco Redi who, in the 17 th century, had performed experiments based on the same principles. In summary, Pasteur boiled a meat broth in a flask that had a long neck that curved downward, like a goose. The idea was that the bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air.
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