It's such a myth, medical students are required to know the reasons for it as part of their anatomy exam and the part 1 examination for foundation doctors includes knowledge of precautions for orthopaedic setting of certain bones in people of Afro Caribbean descent.

It is a fact that the folklore surrounding the reasons dissuades many black people from trying to get on in competitive swimming, I'll agree. Fitness and technique are important factors. Just because my bones move in the right way more easily for many strokes and kicks doesn't mean that I am faster than my mate John. He is younger than me, fitter than me and goes swimming most days at the gym.

Up till recently, misplaced political correctness precluded targeted diabetes screening of people of India sub continent origin, but NICE guidelines threw that out. There are differences between races medically speaking but they are at the susceptibility level in all but UV tolerance of skin. Sadly there are still people who like to use differences for reasons of prejudice. That doesn't mean the point doesn't stand. Susceptibility, not absolute difference.