It has been observed that in general, a word for "mother" tends to be based on a bilabial nasal [m] or similar consonant, and for father it tends to be [b] or [p]. This is found in many language families, so they can't be considered cognates. This is usually explained by the easiness of babies making this sound early in their babbling, so the parents just use those sounds to refer to themselves. However why is it that few languages have used the reverse? (i.e. [p]/[b] for mother and [m] for father)? Wikipedia lists only Georgian, where "father" is /mama/ and "mother" is /deda/.