Blacks, mestizos (what many Mexicans and Central Americans are)and Indians actually have thicker skulls on average than Whites. This is no joke. This gives them an advantage when being hit square in the face, or on the side of the jaw. While these peoples usually have what seems to be bigger jaws, the rear of their jaws, where they connect to the skull, is narrower than that of Whites, another advantage against certain punches. This is due to Whites having larger cranial cavaties. Not PC, but true. Of course, there have been many White fighters with outstanding chins - and I doubt any fighter has ever had the chin of Tex Cobb. He might not have been the best fighter, but he was basically impossible to hurt with a headshot. In a brawl in Philly, when he used the "n" word at a table with Ernie Shavers, a brawl broke out, and someone hit Cobb over the head with a baseball bat. The bat broke, and Cobb beat the daylights out of the guy who swung that bat. No joke.
However - Whites generally have an advantage in endurance and almost always in strength over these peoples, if not an advantage in explosiveness in some cases. This is why Whites easily rule NHB fighting. It is worth noting that some contests have tried to change their formats to match boxing, in the hopes of getting more non-White winners on the podium. You can bet establishment tools like Sen. McCain wail about NHB fighting because of the success of so many Whites.
Whites need more participants in boxing. Then you'll see their numbers rise. I believe there is an economic element - but it's because these days, the "poor" get so much handed to them, including free sports training (not just in boxing) - that even suburban Whites at a local rec center cannot get. The influx of E. European fighters has the establishment scrambling. Promising White fighters were derailed all the time in the 60's and 70's by promoters, the networks, and so on. If enough Euros get into it, the powers that be will have problems stopping the tide.