Example: «Infant pacification may have led to the origins of language». Would it be grammatically correct if I used "might" instead of "may"?
"may" and "might" are nearly interchangeable. The sentence you cite would be equally correct with "might".
"might" is actually less ambiguous than "may", because "may" can mean "has/have permission" as well as "it is possible that".
permission: can, may
possibility: might, may
Can I help you? May I help you? (permission)
I might go shopping. I may go shopping. (possibility)
May I go shopping? Yes. You may go shopping. (permission)
Are you going shopping? I don't know. I may go shopping. (possibility)
"might" is typically only used for permission in reported speech, but even then many speakers do not necessarily change "may" to "might":
Original: He may leave. (permission)
Reported: I said he might leave. [ I said he may leave. ]
Using "might" (as with "could", "would", and "should") often sounds more polite as it tends to give a "distance" between the speaker and the listener. For example, I would never say, "May I go?" to a superior at work, as that seems too impolite. It would always be, "Might I go?"
Where are you from Ailian? "Might I go?" sounds very British. I would only ever say "May I go?" but we probably don't have the same separation of classes here in Australia.
I'm from Louisiana, USA, though I was raised by my extremely polite and proper Creole grandparents (http://en.wikipedia.org/wiki/Creole#New_Orleans_and_Louisiana_Creole
). It's quite normal for others from my area as well as for Cajuns, from what I know, and we also continue to use the subjunctive ("if i were..." et al) and many (myself included) still use a voiceless labial-velar fricative (wh) rather than a voiced labial-velar approximate (w).