There's one thing about evolution I still don't understand?

if we evolved from apes, (meaning our common ansestor, the Australopithecines), why is it that modern apes can't talk? no I'm not taking about sign language, I mean real physical human speech. has any scientific studies ever been conducted on this? also, if we were at one time, an Australopithecine,... show more if we evolved from apes, (meaning our common ansestor, the Australopithecines), why is it that modern apes can't talk?

no I'm not taking about sign language, I mean real physical human speech.

has any scientific studies ever been conducted on this?

also, if we were at one time, an Australopithecine, what is the evolutionary prices for how we developed human speech?

can you please explain this to me?
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