I used to hear back in the 70s that blacks had thick skins, ape like long arms, and heads as tough as coconuts. That, of course, was why they supposedly dominated boxing back then.
Reality tells a much different story, of course. Anyone with a protruding facial bone structure can cut; and whites -not blacks- have the edge in toughness by far. In fact, would you believe that of Bert Sugar's top 20 toughest fighters of all time 19 were white. He gave the number one spot to Hagler though I do not know why. When we think of the toughest fighters of all time we always think of whites, ie: Chuvalo, Marciano, Zale, Monzon, Vitali Klitschko, etc.
Blacks do have a slightly longer reach and thinner bones than whites on average so if they play pitty-pat boxing they stand an advantage to win on points.
Now power, that is clearly, and I mean clearly, a white advantage most of the time. Short, compact punches carry more power. And that is a fact.