Why did fish evolve gills?
If you said, “To breathe,” then you probably passed Biology 101. But you–and the textbooks–may not be right. (From ScienceNOW / by Sujata Gupta) — A new study argues that the structures really emerged to help keep fish in chemical balance with their environment. The first person to suggest that fish develop gills to breathe was Nobel Prize–winning physiologist August Krogh in the 1940s. Later, other researchers expanded the theory, arguing that, as fish became larger and more predatory hundreds of millions of years ago, their rudimentary gills became larger and more complex to help them draw more oxygen from the water. Studies over the past decade have hinted at a different explanation. In order to keep from shriveling like your fingers in the bathtub, fish must constantly exchange ions, such as sodium and potassium, with the water. Larval fish can exchange ions through their skin, and early fish likely used rudimentary gill structures known as branchial baskets. But when the salini
