I’m curious which one you meant by the ‘a sound’.  In the English graphics systems, that glyph represents at least two phonemes (and a couple of allophones, maybe): [a] (IPA lax a) like ‘f*a*ther’ and [æ] (IPA tense a, ash) like ‘h*a*t.’  But there are also similar sounds in the [?] (IPA schwa, no English letter, but like the ‘a’ in ‘*a*bout.’)

Which vowel is easiest to say for a brand new set of vocal systems and neural nets?  Seems like the schwa involves the least effort, and by virtue of being in the dead center middle of the mouth, it might be an easy vowel to articulate.

But this pan-language theory is old news, and sadly this work is in no way conclusive.  Currently, both explanations are equally plausible.  And finding actual evidence to back up either is quite tough.  We have no record the vast majority of human language.  And I swear my 1994 Cable and Baugh textbook mentions this same stuff about ‘mama’ and ‘papa.’  So I’m curious what the meat of this actual study is.

Now, if these studies of the many human languages could come up with something like all languages having 5% of their vocabulary in common, that would be cool.

Merritt Ruhlen has written a book called On the Origin of Languages, which I would like to read.  He claims that all human languages share a common source.  While Ruhlen is a brilliant and respected linguist in other respects, most think this book of his to be nonsense.  At the very least it is nigh on impossible to prove his viewpoint.

Fascinating nonetheless.