I found this article on Acanthostega in Discover magazine, with the
front cover headline "Evolution's Greatest Mystery":
"Most important, Clack and Coates also take with them a deeper respect
for the waywardness of evolution, the habit it has of avoiding what
looks to us like the simple path. Open an evolution textbook and
you're likely to find phrases like "The Conquest of Land," as if it
were manifest destiny that our ancestors came ashore and evolved our
anatomy. "Just because we use our limbs this way now, we can't assume
that that's how they were used in the first place," says Coates.
"There's a kind of horrible foresight to that kind of thinking:
'Better grow myself a limb because my children are going to need it.'
That's why we suggest that limbs evolved in the water for use in the
water, and then they were hanging around on land, and they were useful
there too."
This principle of evolution is sometimes called preadaptation.
There's no foresight involved, though-simply the lucky coincidence
that a feature that evolved to do one thing may turn out later to do
another thing even better. Bone, for example, probably began as a
place where animals could store extra phosphorus; only later did it
support their bodies. Acanthostega, loping around underwater with a
body prepared from head to foot for life on land, may be one of the
strongest demonstrations that we humans owe our existence to
preadaptation's unpredictable nature.
"One gets the impression when reading popular accounts that there was
some kind of imperative, as if tetrapods felt they had to do it, to
embark on the Long March Toward Man," says Clack. "It was much more
accidental than that."
(Zimmer C., "Coming Onto the Land", Discover, June 1995, p127)
A recent Time magazine also contained an article on Acanthostega:
"The drawback for scientists is that nature's shrewd economy conceals
enormous complexity. Researchers are finding evidence that the Hox
genes and the non-Hox homeobox genes are not independent agents but
members of vast genetic networks that connect hundreds, perhaps
thousands, of other genes. Change one component, and myriad others
will change as well-and not necessarily for the better. Thus dreams
of tinkering with nature's toolbox to bring to life what scientists
call a "hopeful monster"-such as a fish with feet-are likely to remain
elusive. Scientists, as Duboule observes, are still far from
reproducing in a laboratory the biochemical are that nature has taken
millions of years to accomplish."
(J. Madeleine Nash, Chicago, "Where Do Toes Come From?", TIME, August
7,1995, p69).