It's a common trend for black athletes to have narrower waists, shorter torsos and longer legs and arms for sure. I wouldn't say this inherently correlates to an advantage though, in wrestling the opposite often seems true, Judo as well...not that black athletes or people with the aforementioned build haven't had success but in general, thicker built guys do better. Beyond that, in boxing you can chalk up a lot of African American success to epigenetics and social influence, less academic opportunity, more recent generations of their families being laborious and physical, disproportionate amount of them pursuing sports in general relative to population and it compounds over time along with creating a strong culture within their communities for it. That said in Russia you see similar with Caucasians, in Asia with combat sports you see similar with certain regions despite small populations and less resources Kazakhs in boxing, Uzbeks in many combat sports etc or look at Polynesians for Rugby in New Zealand and Australia. If it was such a stark advantage, simply put Africans would be winning everything and that's just not the case. There's advantages and disadvantages to all body types and approaches.
