Why has my 16 month old not talked yet?

I have a daughter who is 16 months old. She has done everything early and is very smart. She can walk, run, open doors, crawl and climb on everything, hum along to music, is potty training with great success, off the bottle, can do flips, sleeps in big girl bed because she can climb out of crib, point out colors and numbers, and many other things. She makes sounds of jibberish A LOT! She seems like she is always talking but she still has not even said mama, dada, or anything; just jibberish. Why is this?