How putting frogs in pants led to a scientific breakthrough
No-one had a clue how babies were made — until a scientist in the 1760s put a pair of pants on an amphibian, helping unravel the secrets of life
SILK frog pants.
This strange little garment provided the miracle answer to one of life’s greatest questions: Where do babies come from?
Our most brilliant minds — from Leonardo da Vinci to Isaac Newton — tackled theories on sex and reproduction, but none of them guessed this basic fact that we take for granted: It requires contact between a female egg and a male sperm to create new life.
That big breakthrough came in the 1760s from an Italian priest turned biologist named Lazzaro Spallanzani who attired frogs in hand-sewn boxers — a very early amphibious prophylactic. When the condom-clad Kermits didn’t reproduce, science had a collective a-ha moment, at least where frog sex is concerned.
Still, it was only a beginning, and there were many more questions left to answer about human reproduction. So while our Founding Fathers were drafting the Constitution, “no one in the world knew how fatherhood worked,” writes science journalist Ed Dolnick in his book “The Seeds of Life” (Basic Books), which charts the wildest procreation theories from the past to how we eventually came to understand the origins of life.
THIS is how naïve we were in the late 1700s, even after Spallanzani’s discovery: We believed that staring at the moon could make your kid come out crazy. We thought dreaming of a sexual encounter could get you pregnant.
We might laugh now at the silliness of it all, but it’s really a reminder of how nascent medical science is. We only learned that our heart was a pump in the 1600s. The stethoscope was invented in 1816. The syringe came in 1853. We didn’t know that our blood came in types until the turn of the last century. And there are people still alive who can remember a time before penicillin.
The question — where do we come from? — captivated and plagued early medicine. Even the most seemingly basic questions were incredibly complicated at the time. The female egg may be the biggest cell in the human body, but it’s still only the size of the period at the end of this sentence. Meanwhile, sperm cells are the smallest in the human body. The impossible scale of it all fueled some seriously deranged theories. One scientist in the late 1700s tallied as many as 262 hypotheses on how babies came to be.
In the 1600s, a time people credit as the beginning of science’s modern era, people fell into two camps: Some believed in the “one-sex” model in that women and men had largely the same parts (“the vagina really is a penis and the uterus a scrotum”), while others believed that men had the active repro- ductive organs and women were mere hosts. Dolnick sums up the latter view in one sentence: “Woman was the field where man had planted his seed.”
The role of an egg — inspired by observing egg-laying mammals — has always been a source of debate. Physician William Harvey, who discovered that the heart was a pump, spent a good deal of time searching for the elusive egg by dissecting countless cats, dogs and deer. Though he never found it, his the- ories on the primary role of the egg became the basis for the “ovists,” who believed that God endowed the predetermined egg with an embryo, writes Dolnick.
Dutch scientist Regnier de Graaf grabbed the egg theory from Harvey and went wild with it. He pushed to change the label “female testicles” to ovaries in 1672. He also believed (incorrectly) that he had found the egg while dissecting female rabbits. It turns out that he found the follicle that houses the egg. (To honor his contribution to the field, human egg follicles are named after him.)
Ironically, the invention of the microscope only confused things.
Antonie van Leeuwenhoek, who produced many of the earliest microscopes and documented living bacteria in the late 16th century, found a world under his instrument alive with microorganisms that he named “animalcules.” Semen had particularly aggressive “animalcules” that looked like “tiny eels.” He believed they were parasites. That belief stuck for over two centuries.
But Leeuwenhoek did find evidence of those eel-like animalcules in female dogs after sex, leading him and others to declare themselves “spermists” who believed that life originated with semen, not the egg. Of course God would endow man with the power to create life, they thought.
The answer was clear: Trouserwearing frogs did not create babies, while unclothed frogs did.
OVISTS and spermists warred for another century until the 1760s when Italian biologist Spallanzani came up with the brilliant idea to test the importance of semen by designing pants for male frogs. He cut and sewed scores of tight-fitting miniature boxer shorts out of silk for the frogs to prevent their semen from reaching the eggs (which female frogs lay outside the body, making the mating habits of this animal easier to study). Then he waited to see if the eggs hatched. The answer was clear: Trouser-wearing frogs did not create babies, while unclothed frogs did. Then, Spallanzani took a second step. He grabbed samples from the frog pants, applied them to the eggs and — voila — babies! Studies on other animals replicated his results. Not only was semen key to fertilization, but there also had to be actual contact between semen and eggs to reproduce. While this was a huge step forward, the mysteries of human reproduction remained unanswered for 50 more years. Where was the darn egg?
The answer came in 1827 when scientist Karl Ernst von Baer spied the first mammalian egg in a dog — an experience that he excitedly described like so: “I shrank back, as if struck by lightning, for I clearly saw a miniscule and well-developed yellow sphere of yolk,” he wrote.
This breakthrough moment, Dolnick writes, was met with . . . silence.
Von Baer’s idea gained some traction when cell theory became embraced in the 1830s, as egg cells and sperm cells came to be seen as vital, and importantly equal, building blocks of life. But it wasn’t until 1875 (just four years before Thomas Edison produced a long-lasting electric light bulb, illuminating the physical world) when a curmudgeonly German scientist named Oscar Hertwig truly saw the light.
It all started with Hertwig studying sea-urchin eggs (yes, you can thank delicious uni for enhancing our knowledge of human life).
He dropped urchin semen near urchin eggs and watched as a tiny sperm cell pushed through the egg’s membrane. “Moments later the nucleus of the sperm cell came into view, inside the egg, like a message thrust inside a bottle. Somehow the nucleus of the sperm cell traveled through the giant egg, making its way toward the nucleus of the egg. Suddenly the two nuclei were in contact and then — before Hertwig’s eyes — the two nuclei fused into one. No one in history had ever seen the process of fertilization play out. Until Hertwig,” writes Dolnick.
Hertwig watched for hours as “one cell became two, those two became four, and so on.” He published his findings under the modest title “Contributions to the knowledge of the formation, fertilization and division of the animal egg.” While it sounded mundane, Hertwig’s study was a blockbuster: There could be no further debate about the role of eggs and sperm in the creation of life.
WHILE the mystery was solved, its long unraveling shows how far we have come in medical science — and perhaps how far we still have to go. We’ve now managed to sequence the human genome and clone human stem cells, but we are continuing to learn about our own bodies. In 2013, for example, a new part of the eyeball was identified, and last year we reclassified a part of our digestive system, the mesentery, as an organ. It makes you wonder how much remains unknown — and how many mysteries of today will one day be taken for granted tomorrow. Will we finally figure out the riddle of human consciousness? Dolnick is optimistic. “One day, the answer may be so obvious that nobody will understand how there could ever have been any confusion,” he writes. “In the future, 9-yearolds may read books called ‘Where Ideas Come From.’ ”