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Two Glorious Science Experiments: One About Sex, The Other About Lunch

Wednesday, June 25, 2014 - 07:03 AM

Done right, a good science experiment is simple, clear and revealing. Done splendidly, it's a tale you don't forget. Let's do the sex one first. It took place in Italy, in the 1760s, when a Catholic priest and scholar, Lazzaro Spallanzani, was thinking about sperm — which is why he decided to dress frogs in pants, like this ...

Spallanzani designed 'tight taffeta pants' for the male frogs.
Robert Krulwich/NPR

That's right, pants. Spallanzani was a serious natural philosopher (what we'd now call a scientist); he was also very suspicious of a notion common in his day: that life sometimes spontaneously generates from nonlife.

People noticed that when meat was left on a table for long enough, baby flies appeared. The beef, it was said, birthed the flies. No one knew how. It just happened — poof! Decomposition — even of inorganic things — was key. Put some wheat husks on the ground, mix them with odoriferous human underwear, wait 21 days, and the sweat and the wheat would combine to generate (spontaneously) a mouse. This was a common belief.

Mouse emerging from wheat.
Robert Krulwich/NPR

Spallanzani thought otherwise. He believed that, in higher animals, not only was an egg necessary, but sperm was also required. He believed that life came only from life, not nonlife. Scholars had seen sperm, those wiggly things produced by the sex organ in a flush of solution. Obviously the spermy suspension had some purpose ...

Sperm with a question.
Robert Krulwich/NPR

... but what? So Spallanzani came up with this test.

He acquired a bunch of frogs, males and females. He separated them, and then, for the males, he designed what historians describe as "tight taffeta pants." I'm not sure exactly what they looked like. In some translations, the Italian reads as "short pants," so they might have looked like this ...

Frog hanging from a branch.
Robert Krulwich/NPR

Or maybe like this ...

A frog in pants.
Robert Krulwich/NPR

The pants were then fitted on the males, who, now dressed, were released. Their job, Spallanzani wrote, was to "seek [a] female with equal eagerness and perform, as well as they can, the act of generation."

But with pants on, it wasn't easy.

A not very amorous encounter.
Robert Krulwich/NPR

They got excited, with released sperm staining their garments, but the heavier, wiggly spermatozoa didn't get through.

Spallanzani, of course, had a control group (naked frogs who showered the eggs), and those eggs quickly began to develop, eventually producing tadpoles. But the bepanted frogs?

A sad frog in tight pants.
Robert Krulwich/NPR

They begat no children. The tight pants had clearly removed a key ingredient. Sperm, it seemed, was necessary in these unions. Tadpoles, clearly, didn't spontaneously generate (and didn't, as another group thought, grow from teeny premade versions of themselves). No, Spallanzani proved that baby frogs come from two parents; and while he didn't get the mechanics exactly right, and while he went a little overboard fashionwise with his pant-sized Trojans — Spallanzani had made a major discovery.

To this day, there is a statue in Scandiano, Italy, of Spallanzani holding a magnifying glass in one hand and a frog in the other. The frog, I'm sorry to say, is not wearing pants. Spallanzani is, but you'd expect that. If it had been my sculpture, that frog would have been dressed. I think a teaching moment was missed here, big time. "Mama," I can hear kids all over town asking, "Perché quella rana porta i pantaloni (Why is that frog wearing pants)?" "Ummm," the mother would say, "ask your father."

The second experiment (which I'll get to in my next post) features John James Audubon the great American bird illustrator — and some colleagues, who prepared a delicious lunch for vultures one day. It was a dead sheep, pre-opened and ready for eating. Only this particular sheep wasn't edible. That's because it was a drawing — a drawing sitting on top of real meat. Come back, and I'll explain what happened and why.


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Comments [5]


There was a time when even Aristotle believed that frogs spontaneously erupted from the mud each spring.

Jul. 07 2014 05:52 PM
Holly Dunsworth from Kingston, Rhode Island

Love this story and the drawings! I'll incorporate these images into my lecture slides and attribute them, of course, to you. However...

According to Clara Pinto-Correia's excellent book "The Ovary of Eve," Spallanzani was concerned with semen. He found that semen (not sperm in particular) was necessary. And, in fact, if my reading of history (and her history) is correct, he was not convinced that sperm were necessary!

Jul. 02 2014 07:20 AM

missPooslie, generally "spontaneous generation" (which is what we call it now) was only applied to the smaller animals which we couldn't see mating. Insects, frogs, lizards, worms...especially any organism that seemed to thrive on "icky" stuff like trash, discarded meat etc. They seemed to just appear in the mud, or on bad meat and then they'd be gone.

It was understood at the time that humans and all the larger animals we were familiar with required a male and female to procreate. A lot of this came from the fact that there was an idea of hierarchy with humans at the very top therefore special --> not so special.

Jul. 02 2014 06:08 AM
footloose from California

missPooslie, I'm no expert on the history of science, but I believe that until recently, perhaps even early 20th century, people thought of living creatures as being on a strict linear scale of development with humans at the top and unique. So yes, frogs would be less complex because they're cold blooded and don't look much like people. (I used to live in an extremely arid place with strong seasonal rains. If I'd believed my ears rather than credible authors, I'd have thought frogs magically appeared every spring!)

Jul. 01 2014 06:01 PM
missPooslie from pittsburgh

This is the same question I asked on the NPR post but i only got yelled at on there so maybe somebody on here can explain:

so did they think this spontaneous life only happened with lower life* forms? obviously they would know that humans (and other animals like farm animals) have to mate in order to have offspring, right?

*what they would have considered "lower" life forms. it makes no sense that they would think frogs just magically appear--when farmers have known for 1,000s of years that they have to breed their livestock--unless they considered frogs to be somehow less complex than farm animals. my question is why they thought that about frogs, etc.

Jul. 01 2014 04:49 PM

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