In article <542apq$qsb at mserv1.dl.ac.uk>, Wolfgang Wuster <w.wuster at bangor.ac.uk> writes:
|> The real reason why green fur has not evolved in rabbits or other mammals
|> is likely to be one of phylogenetic constraint - for any mammal to turn
|> green, it would need to evolve, through chance mutation, a green colour.
|> It seems that this has never happened in mammals, perhaps because there
|> are no precursor molecules for a green pigment, or because mammalian fur
|> structure does not allow green appearance through interference colours,
|> as in reptiles. New traits do not appear as if by magic just because an
|> animal needs them - they may appear by mutation, and if they enhance an
|> animal's likelihood of passing genes on to the next generation, they may
|> become fixed in the population, and may allow that population to exploit
|> a new ecological niche.
|>This seems the best answer so far. Many evolution arguments assume that the
organism has complete freedom to evolve how it wants, when of course they
are constrained by their starting point. Clearly existing organisms do enough
to survive, but they needn't have the optimum design. In general, that would be
very difficult since the "goalposts" keep moving as the environment changes.
And since the organism in question is part of other creatures' environment,
you get a complex feedback system which never reaches a stable situation.