Land vertebrates can breathe through their noses thanks to an anatomical rearrangement of fish-style nostrils. That same rearrangement may explain why cleft lips and cleft palates are common birth defects in humans. The nasal passages of land vertebrates differ dramatically from their fish ancestors. In fishes, the nose is independent of the mouth and throat. Water enters the nasal sac through one pair of nostrils and exits through a second pair. By contrast, land vertebrates - technically known as tetrapods, because of their four limbs - have nasal passages that open to the outside world through a pair of external...