- Horse racing rare sport where males and females compete against each other
- Not just jockeys -- but horses. How does gender affect their chances?
- More winning male horses than females, seen as taller, stronger, faster
- Aussie champion Black Caviar, best female thoroughbred in history
Can you think of one sport where men and women compete against each other as equals?
Stumped? Try horse racing, where female jockeys regularly jump in the hot seat alongside their male counterparts.
But it's not just the riders facing-off as they thunder down the track. The horses carrying them towards the finish line are locked in their own battle of the sexes -- and it seems the animal kingdom isn't as different to humans as you might imagine.
While male and female thoroughbreds are fairly evenly matched in physical ability, the girls must overcome commercial and even psychological constraints to get ahead in the sporting world. Sound familiar?
"At the top level, it does take a special filly to beat the boys," Paul Rogers, spokesman at the British Horse Racing Authority, told CNN.
A man's world?
It may seem like quite a stretch comparing women in the workplace to fillies in the field, but just like that so called boardroom glass ceiling, female horses are the minority in the racing world.
Male horses -- known as stallions, geldings or colts depending on whether their manhood is still intact -- far outnumber females -- called fillies -- on the track.
In British flat racing, 63% of horses are male, while 37% are female. It's a similar story for the overwhelming number of male winners -- 67% compared to just 33% for the girls.
Even in America's most prestigious horse race -- the Kentucky Derby -- only three fillies have won in the competition's 138-year-history.
So why do boy horses rule the roost?
"It tends to be that male horses are a bit bigger and taller than females -- a bit like men and women," said Rogers.
"A lot of it also has to do with hormones. Temperament-wise, female horses are probably a bit more placid. And when they come into season -- have their periods -- they can be unpredictable."
That said, stallions -- male horses which haven't been castrated -- can also be flighty, if somewhat more aggressive on the track, added Rogers.
Even playing field?
Yet compare their ability ratings -- zero for a dud to 140 for an unbeaten thoroughbred in the UK -- and both genders score around the same. Males have a median rating of 69, while females score 64.
"While size plays a role -- taller horses tend to have a longer stride -- I wouldn't necessarily say male horses have more stamina," said Rogers.
"In terms of distance, they're probably equally adept. It's more a question of parentage -- if mum and dad are sprinters, then their son or daughter will be the same."
The slight discrepancy in ratings, means male horses will often carry a few extra pounds in weights, to even out the playing field.
Bred for success
The high number of male race horses may also be down to their profitability off the track.
"From a racing industry perspective, if a male horse is successful on the racetrack, they will also be worth a lot more money as a breeding stud -- anything up to around $150,000 per offspring," said Tim Whitaker, head of postgraduate study in equine science at Britain's Duchy College.
"With a mare however, she will only be able to produce one foal a year. But if you get it right -- and it is rare -- you could have a breeding stallion which earns millions."
Perhaps the best example of a super stud's earning power is British colt Frankel, which retired last year with an unbeaten 14-win record.
Today, he commands a fee of $190,000 for each offspring and is expected to generate a staggering $150 million in his stud career.
That said, one of the most remarkable champions the racing world has ever seen also retired last year -- a female thoroughbred called Black Caviar.
The Australian mare notched up 25 consecutive wins, becoming not just a national sports star but a celebrity who even graced the cover of Vogue magazine.
"Her allegiance level is phenomenal," Colin Madden, one of Black Caviar's eight owners, said. "She's a powerful horse who just fronts up every time and people really like that consistency."
The girls may have some way to go in catching the boys. But it seems that even in the equine world, the race is far from over.