Whistling is an odd thing. For most if not all people(i would think), it is instinctual. No learning, no practice required. Somehow we can just whistle a (or any) particular tune. Even if it becomes too high we can automatically switch to a lower pitch, and back again once low enough! How we do that? How we know how to shape our lips?
Did "cavemen" whistle? Was it the first form of musical expression?
Hm, can tone deaf people whistle in tune?
One of the most annoying things ever? A random whistler. No particular tune, just random wanderings. Just stop, stop it.