I've occasionally wondered about this and what I concluded was wherever there are native brown people, there are lethal horrors in the water. White Americans are European stock, there's no crocodiles, venomous snakes or cock intruding parasites in "Caucasian" rivers and lakes, I wonder to what extent the relative fauna of the various environments contributes to black people being largely unable to sit still when "Shit's going down" or "Something's happening". If you've seen a lethal snake then evolutionary pressure may well select for leaping around shouting and waving arms around.