The intent seemed simply to get the infant to look over and make eye contact with the caller, she said, then to amuse the infant, much as a human might try to get a baby to smile.
A rhesus macaque wanting to charm a tot has an advantage over a human: Besides babbling in baby tongues, it can wag its tail. The monkeys often wag their tails in the presence of a monkey infant, like a human using a rattle to entertain the little one.
Evidently, this tail wagging is extremely rare when they aren't in the presence of infants. The article vaguely suggests that this behavior in macaques might be indicative that baby talk in humans might have a biological imperative behind it. That seems plausible to me, given the ubiquitousness of baby talk amongst all human cultures.
The interesting thing is that this could fly in the face of modern critics of baby talk, who believe that using nonsense words and such stunts the baby's ability to learn real words. Of course, my argument would be that the nonsense words don't necessarily have to be a part of baby talk; it seems like the tone, facial expression, and intent alone would qualify.
My wife and I have both had an aversion to using nonsensical baby talk, even before the studies that show that might be harmful (or at least not helpful), but we still do the tone and facial expressions and such with kids. I'm no expert, but it seems like that would both satiate any biological imperatives that exist (plus fulfilling whatever role they play in the baby's development or at least mood), while also not confusing the baby with gibberish. Who knows for sure, anyway? But it is quite interesting...