The deflating news was summarized by Ms. Goodall’s mentor, Louis Leakey: “Now we must redefine tool, redefine Man, or accept chimpanzees as human.”

So what have we actually done now that we’ve had a half-century to pout? In a 50th anniversary essay in the journal Science, the primatologist William C. McGrew begins by hailing the progression of chimpanzee studies from field notes to “theory-driven, hypothesis-testing ethnology.”

He tactfully waits until the third paragraph — journalists call this “burying the lead” — to deliver the most devastating blow yet to human self-esteem. After noting that chimpanzees’ “tool kits” are now known to include 20 items, Dr. McGrew casually mentions that they’re used for “various functions in daily life, including subsistence, sociality, sex, and self-maintenance.”

Sex? Chimpanzees have tools for sex? No way. If ever there was an intrinsically human behavior, it had to be the manufacture of sex toys.

Considering all that evolution had done to make sex second nature, or maybe first nature, I would have expected creatures without access to the Internet to leave well enough alone.

Only Homo sapiens seemed blessed with the idle prefrontal cortex and nimble prehensile thumbs necessary to invent erotic paraphernalia. Or perhaps Homo habilis, the famous Handy Man of two million years ago, if those ancestors got bored one day with their jobs in the rock-flaking industry:

“Flake, flake, flake.”

“There’s gotta be more to life.”

“Nobody ever died wishing he’d spent more time making sharp rocks.”

“What if you could make a tool for... something fun?”

I couldn’t imagine how chimps managed this evolutionary leap. But then, I couldn’t imagine what they were actually doing. Using blades of grass to tickle one another? Building heart-shaped beds of moss? Using stones for massages, or vines for bondage, or — well, I really had no idea, so I called Dr. McGrew, who is a professor at the University of Cambridge.

The tool for sex, he explained, is a leaf. Ideally a dead leaf, because that makes the most noise when the chimp clips it with his hand or his mouth.

“Males basically have to attract and maintain the attention of females,” Dr. McGrew said. “One way to do this is leaf clipping. It makes a rasping sound. Imagine tearing a piece of paper that’s brittle or dry. The sound is nothing spectacular, but it’s distinctive.”

O.K., a distinctive sound. Where does the sex come in?

“The male will pluck a leaf, or a set of leaves, and sit so the female can see him. He spreads his legs so the female sees the erection, and he tears the leaf bit by bit down the midvein of the leaf, dropping the pieces as he detaches them. Sometimes he’ll do half a dozen leaves until she notices.”

And then?

“Presumably she sees the erection and puts two and two together, and if she’s interested, she’ll typically approach and present her back side, and then they’ll mate.”

My first reaction, as a chauvinistic human, was to dismiss the technology as laughably primitive — too crude to even qualify as a proper sex tool. But Dr. McGrew said it met anthropologists’ definition of a tool: “He’s using a portable object to obtain a goal. In this case, the goal is not food but mating.”

Put that way, you might see this chimp as the equivalent of a human (wearing pants, one hopes) trying to attract women by driving around with a car thumping out 120-decibel music. But until researchers are able to find a woman who admits to being anything other than annoyed by guys in boom cars, these human tools must be considered evolutionary dead ends.

By contrast, the leaf-clipping chimps seem more advanced, practically debonair. But it would be fairer to compare the clipped leaf with the most popular human sex tool, which we can now identify thanks to the academic research described last year by my colleague Michael Winerip. The researchers found that the vibrator, considered taboo a few decades ago, had become one of the most common household appliances in the United States. Slightly more than half of all women, and almost half of men, reported having used one, and they weren’t giving each other platonic massages.

Leaf-clipping, meanwhile, has remained a local fetish among chimpanzees. The sexual strategy has been spotted at a colony in Tanzania but not in most other groups. There has been nothing comparable to the evolution observed in distributors of human sex tools: from XXX stores to chains of cutely named boutiques (Pleasure Chest, Good Vibrations) to mass merchants like CVS and Wal-Mart.

So let us, as Louis Leakey suggested, salvage some dignity by redefining humanity. We may not be the only tool-making species, but no one else possesses our genius for marketing. We reign supreme, indeed unrivaled, as the planet’s only tool-retailing species.

Now let’s see how long we hold on to that title.