As I’ll Have Another tries to become racing’s first Triple Crown winner in 34 years, plenty of casual fans will be asking: Why is this feat so difficult? Why is it more difficult than it was in the 1970s, when three different horses in a span of six years swept the Kentucky Derby, Preakness and Belmont Stakes?

Some of the explanations are relatively obvious. Three demanding races in a five-week period constitute a tough grind for contemporary horses, who are generally less robust than their forebears. Moreover, the Triple Crown races draw bigger fields than in the past, because so many owners and trainers are obsessed by winning these events. When Citation swept the series in 1948, he beat 15 opponents in the three races combined. I’ll Have Another had to defeat 19 in the Derby alone.

While these factors are undeniably significant, there is another theory to explain the difficulty of winning the contemporary Triple Crown: The obstacle is not the Triple Crown itself. The real stumbling block is the 1 1 / 2 mile distance of the Belmont Stakes.

Horses who might be Triple Crown-worthy have not often been foiled by losses in the Derby or Preakness during the last 15 years. (One notable exception: Point Given in 2001.) In the same period, however, seven colts have seen their Triple Crown hopes smashed in the Belmont.

During those years, too, a phenomenon has occurred in the Belmont Stakes that is rare in top-level stakes competition. The outcomes of the races have been regularly unexpected or incomprehensible. Ruler on Ice paid $51.50 to win last year. The impossible-looking Da’ Tara (2008) paid $79. Birdstone (2004) paid $74 as he foiled Smarty Jones’s Triple Crown bid. Sarava (2002) defied most handicapping logic when he paid $142.50 as War Emblem lost his chance for Triple Crown. Commendable (2000), coming off a 17th-place finish in the Kentucky Derby, paid $39.60.

Forget about handicapping; if you bet every starter in every Belmont Stakes for the last 15 years you’d have almost doubled your money.

These freakish results in the 11 / 2-mile classic appear to be the culmination of a decades-long trend well known to people in the horse industry. For the benefit of fans who may pay little attention to the sport outside of the Triple Crown series, here is the abbreviated story.

Thoroughbred racing used to be dominated by wealthy dynastic families (the Whitneys, the Vanderbilts, the Phippses, etc.) who bred the horses they raced and imbued them with the stamina they deemed necessary to win the championship events that were contested at distances up to 11 / 2 miles.

Anyone with a rudimentary knowledge of pedigrees can glance at the bloodlines of Kentucky Derby winners as recently as the 1980s and see that these horses were bred to run all day. During that decade, every Derby winner had a high-class 1 1 / 2-mile runner in the first two generations of his pedigree.

But as the racing dynasties diminished in importance, the sport came to be dominated by commercial breeders who sold their foals at auctions. Most buyers at these sales didn’t have the patience of the Whitneys and the Vanderbilts. They wanted fast results, and breeders obliged them by producing horses who were quick and precocious. As sales of 2-year-olds-in-training came into vogue, a youngster who could fly one-eighth of a mile in fast time would often be more valuable than one with the genes to win the Belmont Stakes.

Because of the demands of the marketplace, there was a proliferation of stallions who imbue their offspring with speed rather than staying power. Distorted Humor, More Than Ready and Speightstown were specialists at running only six or seven furlongs, but they ranked among the country’s top seven sires of 2011 and all command stud fees between $50,000 and $100,000. Meanwhile, the marketplace disdains a horse whose chief claim to fame is a victory at 11 / 2 miles. Sarava stands at stud in Florida for a $1,500 fee. Da’ Tara was so lightly regarded in the United States that he was exiled to Venezuela.

The result of these trends, says Barry Irwin, manager of the partnership that owned 2011 Kentucky Derby winner Animal Kingdom, is this simple fact: “In America, nobody breeds a horse for the Belmont Stakes and we don’t breed for a mile and a quarter, either.”

By modern-day standards, I’ll Have Another possesses some respectable stamina influences in his pedigree — though the pedigree is hardly a regal one. (That’s why he sold at auction for $35,000.) His sire, Flower Alley, although a son of the sprinter Distorted Humor, won at 11 / 4 miles in the Travers Stakes at Saratoga. His dam is a daughter of Arch, who won at 11 / 4 miles and sired the Breeders’ Cup Classic winner Blame.

But the results in the Belmont Stakes in recent years suggest that form at 1¼ miles doesn’t guarantee success at 11 / 2 miles; the longer distance is a whole different game. I’ll Have Another is the most talented horse in the Belmont field, but his bid to win it — like almost everybody else’s — will be a roll of the genetic dice.

For Andrew Beyer’s previous columns, go to