Why haven't whales evolved gills?

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Offline thedoc

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Why haven't whales evolved gills?
« on: 29/04/2012 11:25:01 »
Derek Bullen  asked the Naked Scientists:
Why do whales breath air and did not evolve to have gills, the real answer.
Whales are warm blooded. If they had gills the water rushing over their gills would chill their body immediately to below survivable temperatures.
Water is very high density for heat transfer and air is very low. Think of the whales in Antarctica running cold water over their blood vessels in a vascular gill structure large enough to provide oxygen to the large body mass. The whale would have hypothermia in a second.
Whereas man and whale can survive breathing in subzero air.
That is why all warm blooded mammals that live in the sea have never developed gills.
Derek Bullen

What do you think?
« Last Edit: 29/04/2012 11:25:01 by _system »