In the vigorous street theater that is the New York City Marathon, some old truths of long-distance footracing were reinforced Sunday.

Among those: E pluribus unum — out of many, one. That is: While there were 50,000 hardy pedestrians willing and able to navigate the 26-mile, 385-yard trek through New York City’s five boroughs — the annual Running of the Humans — there could be only a single champion in each of the championship divisions.

Eritrea’s Ghirmay Ghebreslassie was the male champ, Kenya’s Mary Keitany the female winner (for a third consecutive year), Switzerland’s Marcel Hug the men’s wheelchair titlist (barely) and American Tatyana McFadden the women’s wheelchair victor (for a fifth time).

At 20, Ghebreslassie is the youngest male New York winner ever, and the youngest since Alberto Salazar’s first of three titles, in 1980, at 22.

Another marathoning certitude: There is no instant health care for pre-existing conditions in this sport. Defending men’s champion Stanley Biwott, who had been dealing with a calf problem the last three weeks, came to the conclusion less than halfway through the race that he could not make it to the conclusion.

Roughly 10 miles into the race, Biwott, the 30-year-old Kenyan, dropped out.

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“At 15 kilometers, I had to realize that I could not make it to the finish line,” said Biwott, who was forced out of the Rio Olympics with stomach issues.

Sunday was the 40th anniversary of the bold — some considered “crazy” — decision to take what had been a quiet cult activity after six years in Central Park and spread it throughout Gotham. From that revolutionary act — which drew 2,090 runners and, in the words of 1976 champion Bill Rodgers, turned New York City’s streets into a marathon “stadium” for unsuspecting spectators — the event has grown exponentially.

Thousands of ordinary people caught what 1972 Olympic gold medalist Frank Shorter called the “disease of running.” Among other extremes, Sunday’s race featured more than 1 million spectators, 12,000 volunteers, 106 clocks along the course, 38 medical stations and $100,000 in prize money to each of the male and female running champs.

But some marathoning realities don’t change. To wit, it seldom is a good strategy to charge immediately into the lead and keep pushing the early pace. American Dathan Ritzenhein, celebrating the 10th anniversary of his first New York Marathon at 33, did that, and by the halfway point, he went from the race’s drum major to losing contact with the dwindling lead pack. By the 15th mile, he was 40 seconds behind. At the 19th mile, his race was over. He dropped out.

Not that a mastery of strategy ever is clear until the end of these things. Keitany, 34, made her 2:24:26 victory appear easy. Only countrywoman Joyce Chepkirui, who wound up fourth, could keep pace with Keitany through the first half, and Keitany was alone for the last 11 miles.

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Not since Grete Waitz’s fifth straight victory in 1986 had a woman won three New Yorks in a row. But, before the race, Keitany revealed that her 3-year-old daughter, Samantha, told her, “Good luck and try not to fall down like in London” — a spill that left her in ninth place and cost her a berth on the Kenyan Olympic team.

Nor was anything guaranteed for Hug, the 2013 New York winner who needed a last-second sprint to edge five-time champ Kurt Fearnley of Australia. (Both were timed in 1:35:39.) “Kurt was killing me on the hills,” Hug said. “I was really not sure to win that sprint, because I was really tired.”

McFadden cruised to her 1:47:43 victory, then declared that her next move is “a vacation,” though she appears to be getting stronger at 27. It was her fourth consecutive New York title and her 17th straight wheelchair victory in the four marathon majors, which include Boston, Chicago and London.

She fits the general belief that elite long-distance performance is the province of the more experienced. But Ghebreslassie challenged that wisdom with his powerful 2:07:51 victory, seizing the lead for good at 20 miles.

Not since Kim Merritt’s victory in the women’s division in 1975 had a 20-year-old been the race’s champion.

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But the marathon still was in Central Park then. Hardly anybody noticed.