In the 1930's someone did a study of the population growth of snowshoe
hares in Canada. At the growth rate then found, if extrapolated backwards
in the same manner as this creationist argument goes, the first snowshoe
hare was created sometime around 1880. But of course that's silly, any
careful look at population growth curves show that not only are they
cyclic (that is they grow and shrink), but the growth phases are rarely
characterized by linear growth rates (which is what the creationists are
proposing), they are usually exponential. This usually results in long
periods of very slow growth until some critical mass is achieved, at which
time the population explodes.
Additionally, a little thought shows how silly this extrapolation is, if
you think about this on the backdrop of recorded history. For example,
take the straight line growth rate proposed by creationists (that starts
with Adam and Eve about 6000 years ago); according to this scheme, when
the Pyramids were being build in Egypt, there were only about 700 people
on the entire earth. When one looks at the extensive archeological
evidence of large construction projects all around the earth (great wall of
china, the Pyramids, Mayan, Aztec and Incan cities, etc), there simply
were not enough people to do the work, if one postulates the growth rate
creationists propose starting with 2 people roughly 6000 years ago.
This argument is one of the most silly arguments of all the crazy
arguments creationists love to throw out. I thought they had abandoned it,
but I guess that would be too much to expect.