It’s tempting to imagine this means that the first humans called their parents mama and dada, and that those two warm, hearty words have survived the slings and arrows of human history to remain in use today. But the notion is too good to be true. Over time in language, sounds smush along their way to becoming new ones, and even the meanings people assign to a word drift all over the place.
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.
Papa and dada happened for a similar pan-human reason. After babies begin making m with their lips, they pick up making a sound that involves a little more than just putting their lips together—namely, putting them together, holding them that way for a second, and then blowing out a puff of air. That’s p—or, depending on your mood, b. Alternatively, babies also start playing with their mouths a little further back from the lips—on that ridge behind the upper teeth that we burn inconveniently by sipping soup when it’s too hot. That’s where we make a t or a d. The order in which babies learn to make sounds explains why the next closest usual caretaker to mom is so often called papa or baba (or tata or dada).
Yes, it is tempting to imagine that the first humans called their parents mama and dada. You can believe that evolution made babies start with two sound groups and emotions immediately tie them to people, or you can believe that God designed us to know what to call our parents from the get go. Simplest answer is likely correct.