Why do the Olympics have the events they have? Why don’t they have swimming obstacle races, croquet, rugby or native mud fighting? The answer is that they once did.

Nowadays, the International Olympic Committee reviews the program for the games every four years and suggests only minor adjustments. And so we always have track-and-field athletics, swimming, gymnastics and a steady roll call of 26-28 other sports. Such was not always the case.

Until the mid-1920s, the events were chosen ad hoc by the local organizing committees.

Since the first modern Olympics were held in 1896, only track-and-field athletics, cycling, fencing, gymnastics and swimming have been on the program every time.

Even within those sports, the events have varied widely.

The Olympics of 1900 and 1904 share the honor of hosting the most unusual sports to have been included. The reason was that both games were held as sideshows to world’s fairs — the Paris Exposition of 1900 and the Louisiana Purchase Exposition of 1904 — and therefore lasted several months.

In 1900, a series of obstacles were set up in the Seine River in Paris. Swimmers lined up for a 200-meter race in which they had to climb over a pole and a row of boats, then swim under another row of boats. That was the only time the 200-meter Obstacle Swim Race was contested at the Olympics.

Also in 1900, cricket was contested for the only time. The match was purportedly between French and British teams, but the French contingent actually was composed of British expatriates working in Paris at the time.

Croquet also was played in Paris, then replaced in St. Louis in 1904 with a variant known as roque. Roque was named after croquet, by dropping the first and last letters, but played with smaller balls and much tighter wickets.

Roque was hailed as the Game of the Century in 1904, but only four Americans competed and today it is essentially defunct.

The organizers in 1904 also had the effrontery to conduct a two-day experiment called Anthropology Days. The exhibits at the fair were designed to demonstrate the progress of humanity from barbarism to the pinnacle of Anglo-Saxon civilization, and this was exemplified by a series of exhibits contrasting various races and peoples, including American Indians and Philippine natives.

The fair organizers thought it would be good to allow the natives to compete, too, in some of their indigenous sports, as well as other more common ones, though this served mainly to mock them. The native peoples — including not only American Indians and Filipinos but also Africans and Syrians — often had no knowledge of the sports they were asked to attempt, which included sprinting and shot putting, but also throwing bolos, mud fighting and climbing a greased pole.

Writing later about the Anthropology Days, Pierre de Coubertin, founder of the modern Olympic Games, presciently said: “As for that outrageous charade, it will of course lose its appeal when black men, red men and yellow men learn to run, jump and throw, and leave the white men behind them.”

Other Olympic sports since abandoned were simply intended to be competitions among all available athletes. Tug of war was quite popular, being held in 1900, 1904, 1908, 1912 and 1920, before falling from the program. Lacrosse was contested in 1904 and 1908, and in 1904, a Mohawk Indian team from southern Ontario placed third. This is why we have Olympic medalists with the wonderful names of Almighty Voice, Black Eagle, Half Moon, Lightfoot and Man Afraid Soap.

In 1900, 1908, 1920, 1924 and 1936, polo was an Olympic sport, falling from grace only after Berlin in 1936. It was the last sport to have been discontinued, until baseball and softball were ousted from the 2012 games. They are to be replaced in 2016 by golf and rugby sevens — a smaller, shorter variant of rugby union.

These two sports won out over karate, squash, roller skating and ballroom dancing — but neither will be new to the Olympics. Golf was contested at those unusual Olympics of 1900 and 1904, and was on the program for both 1908 and 1920, though it was canceled both times.

Rugby tournaments were held in 1900, 1908, 1920 and 1924. The United States won gold twice, in 1920 and 1924 — which is why when the sport returns in four years, the defending champions will be those great practitioners of the game, the U.S.

And so it goes. Many sports want to be on the Olympic program, but many more have left the stage. No, the London organizers will not be placing a series of obstacles in the Thames, and asking the swimmers to make their way over them.

Bill Mallon is a previous president and co-founder of the International Society of Olympic Historians. This column was distributed by Bloomberg News.