Does the Catholic Church accept the validity of the theory of evolution? The answer is both yes and no. While there has been no binding statement of faith issued by the magisterium on this question, several popes and cardinals have addressed the subject. And, their teachings have several common themes.
First, there is no inherent opposition between faith and the scientific discovery that life evolved from lower forms to higher forms over many millions of years. Pope Benedict XVI stated in his address to the Pontifical Academy of Sciences in 2008, "My predecessors Pope Pius XII and Pope John Paul II noted that there is no opposition between faith's understanding of creation and the evidence of the empirical sciences." That's because the Catholic Church does not hold a strictly literal interpretation of the Genesis story of creation, as do some Protestant denominations.
According to the Catechism of the Catholic Church (#337), the book of Genesis "symbolically" presents God's work of creation. In other words, the Biblical story of creation is like a parable in that the plot does not have to be literally true in order for the story to convey profound religious truths, such as the sequential and increasingly complex nature of God's creative activity. Interestingly, the idea of evolution seems to be supported by Genesis 1:24, which states, "Let the earth bring forth all kinds of living creatures." Genesis does not say that God directly created plants and animals in their final form, only that they came forth from "the earth."
Second, even though our material bodies may be the product of evolution, the Catholic Church holds that our immaterial and immortal soul, which makes us truly human, is directly imparted by God. Pope John Paul II stated in his 1996 address to the Pontifical Academy of Sciences, "If the human body takes its origin from pre-existent living matter, the spiritual soul is immediately created by God." TheCatechism of the Catholic Church (#366) also states that "every spiritual soul is created immediately by God."
Third, the materialistic philosophy and naturalistic worldview inherent in much of evolutionary theory is to be exposed and opposed. Materialism denies the existence of anything that is immaterial and spiritual. Therefore, naturalistic evolution (natural causes only) refuses to accept the possibly of God's creative action in the evolution of life. Pope John Paul II stated in a 1985 General Audience, "It is clear that the truth of faith about creation is radically opposed to the theories of materialistic philosophy. These view the cosmos as the result of an evolution of matter reducible to pure chance and necessity."
Cardinal Christoph Schönborn, the General Editor of the Catechism of the Catholic Church, wrote in a letter in the New York Times in July 2005 that, "Any system of thought that denies or seeks to explain away the overwhelming evidence for design in biology is ideology, not science." In the book Creation and Evolution, he states, "The possibility that the Creator also makes use of the instrument of evolution is admissible for the Catholic faith. The question, though, is whether evolutionism (as an ideological concept) is compatible with belief in a Creator. This question in turn presupposes, again, that a distinction be made between the scientific theory of evolution and the ideological or philosophical interpretations thereof."
Cardinal Schönborn also wrote in a 2007 article in First Things, "We must reexamine the genuine science at work in Darwin's theory and its developments, and begin to separate it from ideological and worldview-oriented elements that are foreign to science. Darwin must be disentangled from Darwinism; modern evolutionary theory must be freed from its ideological shackles… The limitation of the methods in the natural sciences to purely material processes cannot do justice to the whole of reality."
Fourth, consistent with the conclusions of many scientists, the Church holds that the undirected, neo-Darwinian mechanisms of random genetic mutation and natural selection alone are inadequate to fully explain the evolution of life on earth. As noted by Cardinal Schönborn in his New York Times letter, "Evolution in the sense of common ancestry might be true, but evolution in the neo-Darwinian sense - an unguided, unplanned process of random variation and natural selection - is not." And, according to the 2004 document of the International Theological Commission, "An unguided evolutionary process - one that falls outside the bounds of divine providence - simply cannot exist."
Therefore, the Church has no objection to the concept of theistic or guided evolution. Theistic/guided evolution holds that if life evolved from a common ancestor, it was God who established the framework, including the finely-tuned set of conditions and governing laws of nature, which enabled life to evolve over very long periods of time into the vast complexity we see today. God could have also guided this process along the way, particularly at the major and often relatively rapid transitions to new and more complex life forms (e.g., from one-celled to multi-celled organisms and the Cambrian Explosion).
In summary, as Pope Benedict XVI proclaimed at his Papal installation ceremony, "We are not some casual and meaningless product of evolution. Each of us is the result of a thought of God. Each of us is willed, each of us is loved, each of us is necessary."