I sometimes wonder if it's an artificial selection thing. I mean, if you're living in a village a long time ago, and you have some chickens running around, and some of them always announce to you when they've laid an egg, and others are sort of stealth chickens so you don't know if they're laying or not, and if you go out to catch a chicken for dinner, well, you're not so likely to eat the one who laid you an egg that morning and made sure you knew about it... so the hens who sang the song would have a better survival rate and the trait would tend to get passed on. I'm curious to know whether the wild red jungle fowl sing the egg song too, or if they're quiet about it.