Surely that if just _some_ living species were the same in some
previous epoch as they are now, that would just indicate that _those_ species
had not evolved during the time since that epoch, but presumably other species
could have. Of course, if _all_ species were the same at _all_ previous epochs
as they are today, then that would presumably be conclusive evidence against
evolution (at least if one knew this to be a fact; if it were only known that
all fossils could be interpreted as those of present species, that would not
absolutely disprove evolution but still would be very strong evidence against
it).
Maybe this shows that for a very well substantiated theory, it is hard
to think of the plausible possibility of a small new piece of evidence coming
in that would disprove the theory, but certainly there is the possibility of a
large amount of new evidence coming in that might, and maybe a sufficient small
bit that would seem extremely implausible according to the present
understanding. For example, if another self-reproducing life form were found
on earth that were based on something radically different from DNA, although
that would certainly not be evidence against the separate evolution of the DNA
life forms and of that life form, it would presumably be evidence against the
idea that both had evolved from a common ancestor that was as complex as life
that requires DNA. (It might be hard to rule out a simple common ancestor at
the chemical level, though even this might look highly implausible, unless one
just says something akin to the unremarkable claim that protons, neutrons, and
electrons are common ancestors for all forms of life, i.e., that all life is
made of "the dust of the earth.")
Another example of an apparently implausible possible new piece of
evidence that could destroy evolution would be a scenario in which God came
down and told us how in detail how and why He created the different species
(both those alive now and those in the fossil record) that have such great
similarities (and with similarities correlated with both spatial and temporal
locations) that it looked like very strong evidence for their evolution.
Someone might not believe that it was God telling us this, but in this
implausible scenario, if indeed He gave a very plausible alternative reason for
why He created the different species without common ancestors, even much more
plausible than the highly plausible common-ancestry evolutionary theory, than I
suspect even atheistic (or previously atheistic) scientists would believe the
new explantation, espcecially if it led to much better predictions for new
observations than evolutionary theory did, such as in enabling us to correct
genetic defects easier or maybe even find fossil fuels more cheaply. (I'm not
necessarily saying that I believe that the previously atheistic scientists
would come to believe that it really is God who came down and gave the improved
explanation; they might claim that it was just an alien from a more advanced
civilization that had found the better explanation, but whatever they thought
of the source of the explanation, if it clearly looked better and led to
improved predictions, I suspect they would adopt the improved explanation,
though perhaps after taking out its theistic elements if they could.)
Don Page