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When Marlo Dewing went shopping for a car last year, she only had one requirement: a manual transmission.

"Any car that was only available as an automatic was a deal breaker," said Dewing, 44. "I love to drive. I want to know that I am actually driving, that I am in control of the machine."

That made her shopping list a very short one. Only around 10 percent of vehicles made in North America now have manual transmissions, down from 35 percent in 1980. And that number is expected to keep shrinking, according to the consulting firm IHS Automotive.

Improvements in the function and fuel economy of automatic transmissions have essentially killed the manual in the U.S., says Jack Nerad, the senior editor of Kelley Blue Book. Some of the country's best-selling sedans — the Toyota Camry, Nissan Altima and Ford Fusion — don't even offer manual transmissions because so few buyers want them. Even some sporty cars, like the Jaguar F Type, come only with automatics.

Two years ago, Chrysler was burned when it assumed there would be higher demand for manual transmissions in its Dodge Dart compact car. The car sold slowly. This year, when Fiat Chrysler's Alfa Romeo 4C sports car arrives in the U.S., it won't offer a manual transmission.

When a manual enthusiast questioned that decision at a company event in May, Fiat Chrysler CEO Sergio Marchionne said U.S. demand for manuals is simply too limited.

"It's going to be you and four guys. That's my assessment of our market demand," he said. "I'll buy one too, but then it's only going to be six."

Manual transmissions — which allow the driver to select the gear — were the rule until 1939, when General Motors Co. debuted the automatic transmission in its Oldsmobile brand. Initially, automatics were much more expensive and got poorer fuel economy, so drivers looking to economize tended to stick to manuals.

But in recent years, those gaps have closed, Nerad says.

"The manual transmission has become kind of a dodo bird," he says.

Manuals no longer have a fuel economy advantage. The five-speed manual transmission on the 2014 Honda Civic sedan gets 31 miles per gallon in combined city and highway driving, for example, while a Civic with Honda's continuously variable automatic transmission — which moves automatically to the gear most appropriate for the car's situation — gets 33 mpg.

The price gap does remain. A Honda Accord with an automatic transmission costs around $800 more than a manual one, while drivers opting for an automatic transmission on a Chevrolet Corvette Stingray have to pay $1,725 more. But that doesn't seem to have stifled demand.

Driving enthusiasts like Dewing remain manuals' biggest fans, and ensure that some brands will continue to produce them. Dewing eventually settled on a 2012 Volkswagen GTI with a six-speed manual transmission. It's a 210-horsepower hatchback that's popular with enthusiasts; Volkswagen says about half the GTIs it sells in the U.S. are manuals.

Dewing, who has two daughters, says she'll teach them to drive on a manual. But Nerad isn't so sure. He taught one of his daughters to drive on a manual, but may not bother for his other two kids. Manuals are disappearing so quickly that they might not ever drive one, he says.

"Most advanced transmissions shift better than I would do," he says. "It's a natural progression. The Luddites out there are decrying the loss of manuals, but I'm not shedding a tear."