Whether it’s a case of friendly cross-pollination or premeditated incest, something curious has been happening between the worlds of boxing, mixed martial arts and professional wrestling. The lines between them have increasingly blurred. Never more so, it would seem, than with Floyd Mayweather and Conor McGregor’s megafight on Saturday on the Las Vegas Strip, which looks to smash pay-per-view and gambling records largely on the strength of combining the top draws from boxing and MMA and packaging the event as WrestleMania.

All three sports — let’s call pro wrestling a sport for simplicity — sell. And all three sports have a history of selling, often for a lot of money, on pay-per-view television. WrestleMania, professional wrestling’s flagship event, was occasionally bought by more than a million households, and some recent UFC engagements have brought in handsome sums in the high eight-figures. A few boxing matches in the past three decades have cracked the 2 million mark, all involving Mayweather — among them, his fights against Oscar De La Hoya in 2007 and Canelo Alvarez in 2013. The Mayweather-McGregor fight is expected to sell 5 million buys at $99.95 a pop. At that total, it would top even the mountainous numbers done by the Mayweather-Manny Pacquiao fight in 2015. Saturday’s bout could be seen by 50 million Americans.

And while that fight could make $1 billion all told in a single night, the early incentives for cross-pollination were poverty and despair. If you’re searching for storybook endings in American life, boxing is one of the worst places to look — and has been for well over a century. It’s left many of its most iconic heroes broke or buried under debt — and in some cases, desperate for a payday.

Even after earning upwards of $5 million in his career, former heavyweight champion Joe Louis found himself $500,000 in debt to the IRS and had to keep going until Rocky Marciano literally beat him from the ring and into retirement in 1951. Louis was still in debt but had a crazy idea to try and keep the IRS off his back. Sixteen years before, Louis had knocked out Primo Carnera, a gargantuan Italian former world champion known as the the “Ambling Alp” at Yankee Stadium. Carnera had fought 102 fights over 18 years and, surprise surprise, also managed to leave the sport broke. Before the year was out, Carnera gave professional wrestling a whirl. He was undefeated in his first 120 matches — staged though they were. This all sounded too good to be true for Louis, and so he followed Carnera’s lead. And pretty much every era-defining prizefighter has, too: Muhammad Ali, Joe Frazier, Mike Tyson and, most recently, Floyd Mayweather, who took on the 7-foot, 400-pound “Big Show” at WrestleMania XXIV.

Prominent boxers have also ventured into MMA’s octagon with not entirely promising results — and this is an actual blood sport we’re talking about, rather than a prearranged show. That list includes former heavyweight champion Riddick Bowe, three-weight world champion James “Lights Out” Toney and Olympic heavyweight champion Ray Mercer. In what would be both his first and last match, Bowe was knocked off his feet five times by kicks to the shins. He eventually collapsed in the second round clutching his shin, and the bout was stopped. He retired from MMA with a record of no wins and one loss. Toney’s entire MMA career proved even more brief, after losing in the first round to Randy Couture. Mercer fought two kickboxing matches (lost both) before moving on to MMA. He embarked on his MMA career with an exhibition against Kimbo Slice in 2007 and was promptly choked into submission. Yet Mercer gained his redemption in his — to date — only official MMA bout, punching Tim Sylvia’s lights out after all of nine seconds.

Brock Lesnar, who in 2002 defeated “The Rock” to become the youngest WWE champion in history, is one of few to make the transition from the staged rings of pro wrestling to actual, professional combat. After first trying his hand at NFL — he got as far as a few preseason games with the Minnesota Vikings — Lesnar turned to MMA in 2006, first fighting in the K-1 Mixed Martial Arts League. Soon the UFC came calling and signed Lesnar, who had been an NCAA champion wrestler for the University of Minnesota, to a contract in 2008; he would go on to fight in several major pay-per-view fights for the UFC, including four that sold over a million buys.

McGregor isn’t the first superstar to move from the octagon to the boxing ring. One of MMA’s greatest fighters, Anderson “The Spider” Silva, tried the same thing back in 1998. He faced the not-exactly-household-name Osmar “Animal” Luiz Teixeira and after all of six minutes, Teixeira’s pugilistic skills proved too much for fellow Brazilian Silva. To protect him, Silva’s corner threw in the towel in the second round. Silva’s unparalleled genius in the octagon translated into his losing to someone even charitably described as a journeyman boxer; if this is any litmus test of what to expect from McGregor squaring off against Mayweather — one of boxing’s all-time greatest fighters — the current +400 money line somehow doesn’t reflect it.

McGregor isn’t even the first UFC superstar to express an interest in fighting Mayweather. In 2014, MMA’s biggest star, Ronda Rousey, issued a challenge to Mayweather to fight her in an intergender MMA bout. Perhaps Rousey took her inspiration for proposing this fight from the world of boxing, where the first ever licensed intergender fight took place at Seattle’s Mercer Arena in 1999, between 36-year-old boxer and landscaper Margaret MacGregor (no relation) and Canada’s Loi Chow. MacGregor won every round. Only this week, rumors were swirling that Rousey would leave behind her two iconic losses and MMA career to join the ranks of the WWE.

Speaking of pivoting to new careers and rising to unexpected heights, the cross-pollination among these fighting sports has recently reached a place of prominence in American life. President Trump, a prominent character in both boxing and professional wrestling, solidified his bona fides for the Oval Office with his tenure on “The Apprentice,” exploiting this dynamic better than anyone.

But it didn’t start with Trump, and it won’t end with him, either.

Win, lose, draw — or disqualification — Conor McGregor’s antics in the lead-up to his contest against Mayweather have amounted to what would be the greatest audition tape ever sent to Vince McMahon. If that audition were successful, it would make him the first crossover star to participate as a showcase attraction, at the highest level, in MMA, boxing and wrestling. The Triple Crown of spectacle.