Krulwich Wonders...
9:56 am
Fri May 17, 2013

What Did I Do Last Summer? Oh, I Discovered How To Make Babies Without Sex. And You?

Originally published on Fri May 17, 2013 11:26 am

Ah, if only all summers could be like June, July and August 1740 — when three young guys (and a 6-year-old and a 3-year-old) did a science experiment that startled the world. In those days, you could do biology without a fancy diploma. More people could play.

That spring, the hot book — the one everyone was reading — was a gorgeously illustrated volume about insects by the French naturalist René Antoine Ferchault de Réaumur. It was called Mémoires pour servir a l'histoire des Insects and in it, Réaumur mentioned that in all his years looking at bugs — and he was a very good looker — he had never seen a male aphid.

Babies Without Sex? Is It Possible?

"Where are they?" he wondered. Female aphids you find everywhere, on the undersides of leaves, on branches, on any number of plants. But males? Never.

Consequently, Réaumur said he had never seen the act of "aphid coupling." Could it be that aphids are extremely discreet, or maybe, just maybe, they can reproduce without sex! With the biblical exception of the Virgin Birth, sex was considered the universal method of reproduction. But, Réaumur wondered, what if it isn't?

Réaumur, in his book, said he had tried to figure out how aphids reproduce but didn't have the time to do it right. Instead, he invited his readers to take the lead. And in the spring of 1740, one of those readers, a 20-year-old law student in Switzerland named Charles Bonnet wrote Réaumur to say he was going to give it a try.

The Virginal Aphid Experiment

The plan was to get a female who had never ever had any contact with a male — a Total Virgin — watch it very closely, and see what happens.

To do that, Charles took a newborn female aphid from its mother immediately after its birth — before it could be exposed to any other aphids — and put it in an isolation chamber (on a plant leaf stuck into a container of water, inside an overturned glass jar) like this ...

... Then he watched from early in the morning — 4 or 5 o'clock — all day long till 9 or 10 at night, for 12 days, keeping his eye on his female "little prisoner" to make absolutely sure no insect — and definitely no male aphid — could make contact.

The baby female, meanwhile, nourished by the green spindle tree leaves in the glass tank, grew, molted, ate more, grew more, then molted again. Using a magnifying glass to watch, Charles Bonnet worried that she might slip from the leaf down into the pot and disappear in the soil below — but she held on, reached sexual maturity without ever having met, seen or in any way encountered a male aphid. And yet, amazingly, on the evening of June 1, 1740, at 7:30 p.m., this little lady gave birth to a brand new baby. A female. Charles Bonnet saw her do it.

Then over the next 21 days, she delivered 94 more. How she did it, Bonnet could not say, but that she did it, was unarguable.

Here are his lab notes, listing each of the 95 births. ("Pucerons" or "puc" are aphids. He put asterisks alongside births he didn't actually see.)

Charles Bonnet then sent these notes, his findings and a cover letter on to Réaumur in Paris, who, enormously pleased with the discovery, read Bonnet's letter in July to the assembled members of the French Academy of Sciences in Paris. The next step, clearly, was to repeat the experiment, to see if another virgin would produce another batch of babies.

Bonnet had two young friends, 34-year-old Pierre Lyonet, (a lawyer at the Hague) and 30-year-old Abraham Trembley, a private tutor in Holland. Each was an avid insect collector and a big fan of Réaumur and his book. So at Réaumur request, they agreed, each of them, to repeat the experiment: to catch a baby aphid, isolate it and see if it reproduced.

The Bentinck Boys Join In

As it happens, Abraham Trembley, the tutor, was spending that summer on a vast estate in Holland, not too far from the Hague — home to enormous gardens, lots of insects, including a great many aphids — plus two little boys.

One of them, Antoine Bentinck, was 6 years old. Jean, his younger brother, was 3. Abraham, their tutor, taught them to read, write and hunt for insects. Their parents, Count and Countess Bentinck were squabbling that summer. She had run off with a lover to Germany. He was suing her for divorce. Neither had time for the boys, so Abraham was more or less their parent that summer, and when he signed up to do the aphid experiment, he told the Bentinck boys they were going to help do it with him, telling them, writes author Rebecca Stott, "that they were now engaged in a serious investigation that might put their names into the annals of science."

So Abraham and the boys found another just-born aphid, put her in a similar jar, watched her grow, molt, reach maturity, watched her night and day, and the Bentinck aphid, like the Bonnet aphid (and, eventually, like the aphid from a third experiment, the Lyonet aphid), all produced babies.

"The Law Of Coupling Is Not A General Law"

When word of their findings got to Paris in August 1740, Réaumur sent his young (and very young) colleagues a letter of congratulations. "These are assuredly observations of great importance in natural history," Réaumur wrote Charles Bonnett, "since they each show us that the law of coupling is not a general law."

This little gang of amateurs had together toppled "one of the central premises of 18th-century science," says Rebecca Stott, "the belief in the universality of sexual reproduction." They had just discovered parthenogenesis, the ability to reproduce without sex.

Show Me The Daddy!

For a while, skeptics insisted that the baby aphids had been impregnated in earlier generations and that fertile embryos had somehow been passed from mothers to daughters. The following summer, in July 1741, Charles Bonnet raised a series of virgin aphids for five generations, and all of them successfully produced offspring. The next summer, in 1742, he ran the experiment for nine generations, and still they produced babies. This, it seemed clear, is something aphid females can do.

So what about Réaumur first question, the one about the missing dads? Where are the male aphids?

They show up. Charles Bonnet saw one — but not in Spring. When the days get short and the weather turns cold, female aphids begin producing males, who do what they're supposed to — mate with the females. And their eggs (in springtime, aphids produce live births; in fall, eggs) are stored over the winter until it's time to reproduce again.

When Bonnet saw his first male, he wrote his tutor friend Abraham Trembley to say that it was roaring sexual, "perhaps one of the most ardent that there is in nature. It appears to me that it does nothing except have intercourse as soon as they day arrives."

Making up for lost time, one supposes. You know, as Bonnet might have said, "guys."


I read this story in Rebecca Stott's book Darwin's Ghosts: The Secret History of Evolution. You can also learn more details here.

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