>adaptation would set in in a noticeable way only when the climatic changes
>were killing off a major portion of the population. And, obviously, if the
>climatic change was *too* fast and too severe, it would simply kill the
>species off in that area.
It is to the advantage of the species to *not* be perfectly adapted to its
environment. The Giant Pandas and the Koalas are cases in point. They can
only eat one kind of food. Humans are threatening those food sources and
they are dying out. It need not have been us that wiped out that food
source. A plant blight that killed only bamboo would have done the trick
for the Pandas and their birthrate is so low they could never have evolved
fast enough to adapt.
An interesting example of this from human history is the Irish potato
famine. The Irish depended almost exclusively on the potato as a staple
food source. All of the potato plants in Ireland at that time were
originally from just (as I recall) three plants. Two evolutionary events
then converged. The first potato blight that happened by wiped out nearly
all the potato plants because not enough variations had accumulated in the
short time since potatoes had been introduced in Ireland for enough of the
plants to resist. AND the Irish were too "perfectly adapted" to their
"potato environment." Fortunately for the Irish, as opposed to the Pandas,
the dependence on a single food source was brief and rather "unnatural."
Oh, and I agree with Chris that any evolution would have taken place
*after* the natural disaster, not *during*, depending on how fast the
"Life itself is the proper binge."