Its because Mexicans tend to fight below the weight of 154 whereas blacks and whites are gentectally larger men that rarely fight below 160. I mean the human head size doesnt different much from height to height so of course a smaller man would appear to have a larger head because its bigger PORPORTIONALLY.

You compare getting punched by guys like Tyson, Lewis, Klitschko, or Briggs to being punched by Chavez, Barrera, Morales, or even Duran the bigger guys would cause much larger brain damage.

Seriously the Heavyweights honestly average 100lbs more than the Mexican fighters. I can easily see why they get punch drunk more often.