Where Mom Comes From

So lately I've had a theory about how the word "mom" came about. Have you ever listened closely to a baby crying and that "mmmmmuuum" sound comes out. My theory was back in cave man times babies made this lovely sound (while crying) and the female would of course meet her child's needs and thus she was dubbed "mum". This word eventually evolved and is now mom. So that's how we became mom, all because a baby cried. To further my theory the word "dad" is more of a fun sound brought about usually while laughing. So "dad" gets the fun, laughing name and we moms get the cry, how does that work? Obviously there is no research behind this theory; just me and my mom thoughts :)