In 2007, a 15-year-old chimpanzee named Julie started sporting a stiff blade of grass behind one ear — a trend that drove her fellow apes wild.

First, her son donned his own ear ornament, followed by eight other chimps in Julie’s troop of 12, who all lived in a sanctuary in Zambia.

When Julie died in 2012, her local gang kept wearing the single-blade accessory, and the style eventually spread to fashion-forward chimps in two nearby populations.

Julie and her fellow fashionistas were likely copying each other “just to be in with the in-crowd,” writes Adam Rutherford in his book, “Humanimal: How Homo Sapiens Became Nature’s Most Paradoxical Creature — A New Evolutionary History” (The Experiment), out now.

They’re not the only beasts to display human-like behavior — whether it’s a creative use of tools, enjoying recreational sex or harnessing fire, it turns out that animals are often just like us.

It’s well known that chimpanzees use sticks to dig termites out of holes, but many other creatures also get smart in the quest for tasty snacks. As recently as 150 years ago “we thought we were the only organism to use tools,” Rutherford told The Post. “But now we know 1 percent of species do.”

Take bottlenose dolphins in Shark Bay, Australia. These resourceful sea mammals wrap live sponges around their beaks to scrounge for spiky bottom feeders. Crows — no bird brains — use sticks as hooks to root out grubs. “That shows an astonishing level of analogical reasoning which allows them to think a few steps ahead,” Rutherford said.

Australian birds of prey will pick up burning sticks from a bushfire and drop them in a dry grassy area to ignite a blaze — then await the dinner bell as small animals flee.

These pyromaniac hawks could explain why wildfires often start in odd places. “It’s also possible Australians learned to start fires from so-called firehawks,” said Rutherford. “It’s insane.”

Meanwhile, don’t assume that humans are the only animals having sex for fun. Fornication among the horniest creatures on the planet — bonobo primates from the Congo Basin — is “unmatched among animals, including us,” said Rutherford.

Bonobos engage in some type of sex act an exhausting 10 times a day yet have babies just once every five or six years. A bonobo bundle of joy comes along only once out of 18,250 sex acts, while humans conceive roughly once out of every 1,000 acts of heterosexual intercourse.

“Bonobos are very weird,” said Rutherford. “They’ve been isolated on the left bank of the Congo River for more than a million years. All social engagements involve some sort of sexual congress.” Sex — including same-sex sex — is used for greetings, resolving conflicts, asserting the social hierarchy or just showing excitement over a meal.

“It’s proper science,” Rutherford noted, “but it’s pretty entertaining.”