Evolution of blind cave fish
I am a biology teacher, now starting a unit on evolution.
Just about every book on the topic mentions the blind and albino cave fish. But I've
always been bothered by this example. Why is being blind and white an advantage for
animals in a cave? I understand that they have no use for eyes or pigment, but this
sounds like we're back to Lamarck's law of use and disuse.
Wouldn't there first have to be the mutations to cause these? And in order for the
changes to become common, they would have to be advantageous. Although there is no
use for the eyes or pigment, what is the advantage to losing them?
I can think of one important use for the loss of pigment in fish. It has
been documented with the early breeding of black mollies and black angelfish, that
the fry were extremely hard to keep alive. The breeders found that these fish required
much greatly quantities of protein to produce the pigment melanin, and therefore
supplementing the fry with protein quantities that were many times higher than those
required by less pigmented fish kept them alive. Imagine then, a situation where a
random mutation of albinism in a cave dwelling fish results in a population that can
use the protein that it consumes for growth and reproduction, rather than for pigment
production. The albino fish could quickly out-produce the pigmented fish. What the "real"
explanation would be as described by an evolutionary biologist, I have no idea.
Click here to return to the Biology Archives
Update: June 2012