The Atlantic explains Why the Words for ‘Mom’ and ‘Dad’ Sound So Similar in So Many Languages
The answer lies with babies and how they start to talk. The pioneering linguist Roman Jakobson figured it out. If you’re a baby making a random sound, the easiest vowel is ah because you can make it without doing anything with your tongue or lips. Then, if you are going to vary things at all, the first impulse is to break up the stream of ahhh by closing your lips for a spell, especially since you’ve been doing that to nurse. Hence, mmmm, such that you get a string of mahs as you keep the sound going while breaking it up at intervals.
Babies ‘speaking’ in this way are just playing. But adults don’t hear them that way. A baby says ‘mama’ and it sounds as if he’s addressing someone—and the person he’s most likely addressing so early on is his mother. The mother takes ‘mama’ as meaning her, and in speaking to her child refers to herself as ‘mama.’ Voilà: a word mama that ‘means’ mother. That would have happened with the first humans—but more to the point, it has happened with baby humans worldwide, whatever language they are speaking. That means that even as the first language was becoming countless others, this ‘mama mistake’ was recreating ‘mama’ as the word for ‘Mom,’ whatever was going on with words like mregh.