Baby's first word is always a big milestone, but now we may know why that first word is often "mama" or "dada." According to a new study published in the Proceedings of the National Academy of Sciences, it's all about sound. In many cultures, the words for "mother" and "father" feature repeating sounds and babies are particularly drawn to that.

Researchers discovered baby's preference for repeating sounds by doing brain scans of newborns while listening to recordings of made-up words-the "words" with repeating sounds caused increased brain activity. Of course, baby's attachment to mom and dad doesn't hurt, either.

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