ARN's "The ID Report" web log has isolated simply and easily why fully naturalist evolution, fully dependent on random mutation, natural selection, sexual selection, and similar fully material processes, is not compatible with the teaching of the Church. Naturally ARN does not do so explicitly, but it is there for all to read who are at all familiar with the crucial and central nature that the doctrine of free will holds. It is not incidental to our faith. Some of you will be quick to point out that Pope John Paul the Great, in one of his writings, said that evolution can be compatible with the faith. He is, naturally, correct, it can be. But recall, he said this after stating that there is no single theory of evolution, but rather many. Here also he is accurate. Evolution as simply change within a species[2], what intelligent design proponents would call "microevolution," is fully compatible with our faith. Evolution understood to allow and be a directed process, directed by God with His goals in mind, is also compatible. In such a theory, God would simply be choosing to hide His hand behind seeming randomness. Scientists who are debating against the inclusion of intelligent design, or even against teaching the flaws and short comings in evolution theory, across the country are not however, open to either of these understandings of evolution. While the Pope was right, science, as it exists institutionally (rather than as a process) is insisting on being wrong.
Returning to the topic at hand, if then, we look at evolution only in its fully materialist forms, you come down to genes, or some super-set largely consisting of genes (there is now, remember, some unknown mechanism by which 2 wrong copies of a gene may be corrected), determining everything about the human person. Taken to its logical extreme by some of the social Darwinists (who, to give biology its due, are mostly not biologists), this would hold true even of human actions and motivations. Evolution, understood in fully material terms, destroys free well. We become simply biological computers responding to stimuli in complex but ultimately (given sufficient computing power) predictable ways. If there is no free will, there is no sin, no sin, no Fall. If there was no Fall, there was no need for a Savior, and our faith is without foundation. Moral relativism, in all its darkness and with all its potential for despair (despair we are seeing today in the high suicide rates), is ushered in.
[1]
http://www.arn.org/blogs/index.php/2/2005/05/17/can_a_gene_really_make_you_fat
[2] "species" is a defined word in biology. The boundry of a
species is defined to be the subset of organisms that can produce
fertile offspring. Thus while a great dane and a toy poodle are
unlikely to ever mate, and perhaps even could not, yet you
cannot define them as separate species because each is clearly linked as
the same species as other, ever more mid-sized dogs, whose offspring are
fertile. On the other hand, the horse and the donkey can and do mate,
but as the mule is not fertile, they are separate species.
Interestingly, scientists throw out this definition whenever convient,
for instance, the wolf is still held separately from the dog, and botany
appears to ignore this definition entirely.