“Fifty thousand years ago there were these three guys spread out across the plain and they each heard something rustling in the grass. The first one thought it was a tiger, and he ran like hell, and it was a tiger but the guy got away. The second one thought the rustling was a tiger and he ran like hell, but it was only the wind and his friends all laughed at him for being such a chickenshit. But the third guy thought it was only the wind, so he shrugged it off and the tiger had him for dinner. And the same thing happened a million times across ten thousand generations - and after a while everyone was seeing tigers in the grass even when there were`t any tigers, because even chickenshits have more kids than corpses do. And from those humble beginnings we learn to see faces in the clouds and portents in the stars, to see agency in randomness, because natural selection favours the paranoid. Even here in the 21st century we can make people more honest just by scribbling a pair of eyes on the wall with a Sharpie. Even now we are wired to believe that unseen things are watching us.”
I think this also explains the survival advantage of apparently hearing your phone ring while you're in the shower. Those who heed the faint beckoning get the benefit.
A listener on night shift guard duty from a more ancient or more naturalistic culture would perceive it as spirits trying to send him a message (probably just his subconscious working something out, but whatever it doesn't matter) so he's listening really close to the spirits muttering and then "snap", oh foul words, that was a real sound from a real hungry lion, sound the alarm.
Meanwhile people who hear nothing in the wind get bored, fall asleep, and become snack for hungry lion.
This is ignoring the second order effects of most of the voices are probably your subconscious working something out of your system that needed working out, so you'll be a more well adjusted caveman if your PTSD is worked out because of something you heard the spirits tell you on the wind, than if its all bottled up.
― Peter Watts, Echopraxia