"95% to 98% of people choose kiki for the angular shape and bouba for the rounded one... Even 2.5 year-old children (too young to read) show this effect."
"Ramachandran and Hubbard suggest the kiki/bouba effect has implications for the evolution of language, because the naming of objects is not completely arbitrary. The rounded shape may intuitively be named bouba because the mouth makes a more rounded shape to produce that sound, while a more taut, angular mouth shape is needed to articulate kiki. The sound of K is also harder and more forceful than that of B. Such "synesthesia-like mappings" suggest that this effect might be the neurological basis for sound symbolism, in which sounds are non-arbitrarily mapped to objects and actions in the world."