I keep thinking I’ve already posted this link here and keep finding I haven’t, so here it is.
http://www.sussex.ac.uk/linguistics/documents/where_do_mama2.pdf
Yes, yes, it’s pdf, but it’s worth it. The late linguist R. L. (“Larry”) Trask puts into very clear terms Roman Jakobson’s explanation for the fact that so many languages have words for “mother” that sound like “mama” and so many languages have words for “father” that sound like “papa.”