Four-time Olympic gold medalist Michael Johnson said he believes the reason black athletes tend to dominate certain competitions is because the descendants of slaves have a "superior athletic gene."

The retired American sprinter, who recently traced his lineage back to West Africa as part of a British documentary, told the Daily Mail slavery has left "an imprint through the generations."

"Over the last few years, athletes of Afro-Caribbean and Afro-American descent have dominated athletics finals," Johnson said. "It's a fact that hasn’t been discussed openly before. It’s a taboo subject in the States but it is what it is. Why shouldn’t we discuss it?"

The Mail explained:

Some scientists believe a combination of selective breeding by slave owners and appalling conditions meant that only the strongest slaves endured, creating a group predisposed to record-breaking athletic performance.

African slaves underwent a rigorous selection process and only the fittest were transported on ships.

"All my life I believed I became an athlete through my own determination, but it’s impossible to think that being descended from slaves hasn’t left an imprint through the generations," Johnson said. "Difficult as it was to hear, slavery has benefited descendants like me – I believe there is a superior athletic gene in us."

For good reason: It's a third rail topic in the States. Even intelligent debate on the subject runs the risk of becoming controversial. Any statement is treated as polarizing.

The comments section on the Daily Mail piece is a fine example. Either Johnson is a hero for bringing his views to light or he's ignorant for his "trash" beliefs. There's no middle ground in a topic like this.