On a related but not-at-all-the-same note, babies are able to hear and distinguish between every single intonation that humans make in our myriad languages, but we lose that ability and become only able to distinguish the ones in the language(s) we're exposed to growing up.

I've noticed there are some tonal differences that I can hear--having grown up around both English and Chinese speakers--that the hubby can't.

Another argument for having kids be exposed to as many languages as possible.