Career Aptitude Tests - Nature vs. Nurture

If they ever develop a really good test for career aptitudes, what correlations they would find? Gardeners <-> biologists, mechanics <-> computer programmers, waiters/tresses <-> actors/actresses? But every waiter is an aspiring actor so it would be hard to separate nurture vs. nature. Are they called waiters/resses because they're all waiting to become actors/tresses?