The world may run out of elephants. Poachers kill an estimated 40,000 of the big animals a year, even though trading in ivory has been essentially illegal for more than 20 years.

But 150 years ago, ivory was booming and nobody worried about elephants. The gorgeous material could be shaped into lots of things — and was. But for one entrepreneur, ivory’s specialness was a big problem.

That man was the father of American billiards — and the his ivory problem made him, in a sense, the grandfather of the modern world. Which is to say, of plastics. 

It’s tempting to call Michael Phelan the Steve Jobs of billiards.

“I think that would be an understatement,” says Michael Shamos, author of “The New Illustrated Encyclopedia of Billiards.”

“While Steve Jobs did amazingly brilliant things, he was not fully responsible for the computer,” says Shamos, who is a computer-science professor at Carnegie-Mellon University. “But Phelan, in many ways, was responsible for the uptake of billiards in the United States.”

And billiards, says Shamos, was the single most-popular amusement for men in the second half of the 19th century.

Phelan was the top player, a best-selling author, and the first big manufacturer of billiards tables.

To popularize the game, he helped standardize the gear — which, in the case of the balls, meant maintaining a very high standard.

“The billiard ball has to have certain physical properties,” Shamos says. “It has to rebound properly. It has to be of uniform density.”

In the 19th century, that meant it had to be made of ivory, which wasn’t cheap. 

What’s more, billiard balls required the top grade of ivory, much of which was wasted in the process. 

“The average number of billiard balls that could be obtained from a single tusk,” Shamos says, “is three.”

Phelan and his partners saw the reliance on ivory as a threat to his industry’s growth. It was as if the Apple Watch could be sold only in the $10,000 gold edition, because the gold was necessary to make the device function.

“They were really desperate, I don’t think is too strong a word, to find some kind of substitute material,” says Robert Friedel, a professor at the University of Maryland and the author of the book “Pioneer Plastic: The Making and Selling of Celluloid,” which tells the story of what happened next.

Phelan advertised a prize of $10,000 — the equivalent of almost $3 million today, compared to the wages earned by laborers at the time  — for the discovery of a satisfactory substitute for ivory in making billiard balls. The contest prompted a printer named John Wesley Hyatt to experiment with a newly discovered material, nitrated cellulose: cotton fiber treated with nitric and sulfuric acid.

“That material turned out to have very interesting properties,” Friedel says. “In particular, it dissolves, and it creates a kind of syrupy liquid.”

After more than five years of tinkering, Hyatt produced the first plastic, which he called celluloid — but it doesn’t win Phelan’s prize.   

“Celluloid is a wonderful material,” Friedel says. “It’s a beautiful plastic, and it has a wonderful range of uses. But. Billiard balls is not one of them.”

Balls made with celluloid just don’t bounce right.

Hyatt looked for another market, and eventually found a hit, producing fake ivory for knick-knacks: knife handles, combs, hand mirrors, all kinds of things. 

“Celluloid a terrific faux-ivory,” Friedel says. “And it’s a great faux-tortoise-shell, and amber and coral — there are all sorts of great effects you can get from it.

Billiard balls kept getting made out of ivory. Which was OK — for the billiards industry anyway —  because Europeans keep colonizing and exploiting more of Africa. It was not great for the people of Africa, as documented in books like Joseph Conrad’s “Heart of Darkness” and Adam Hochschild’s “King Leopold’s Ghost.”

It was also terrible for elephants. By 1910, the elephant population had dropped to the point where billiard-ball makers, among others, were getting acutely worried about the ivory supply.

Right around then, a chemist named Leo Baekeland came up with a new kind of plastic, made from petroleum, naming it bakelite, after himself.

Among bakelite’s advantages: It could be liquefied during production, and fillers could be added.

“With that capability,” Friedel says, “you can vary the density, you can vary the elasticity— and you can make a perfect billiard ball.”

Celluloid got supplanted by newer plastics except for one key use, one product for which celluloid is said to perform better than any other material: ping-pong balls.

Celluloid balls got bumped from tournament play just last year. It was a controversial decision.