The fact the pope wants to hear from others, however, by no means implies that he lacks ideas of his own. Over the years, Joseph Ratzinger has wrestled with the theory of evolution in books, articles, lectures and interviews, including a 1990 book-length commentary on the Genesis creation stories.

Whether that past will be prologue to anything Benedict does as pope is still unclear, but these sources, examined at length by National Catholic Reporter in recent weeks, at least provide a picture of his approach.

What do they reveal?

First, Benedict XVI is not a “creationist.” He does not advocate a strictly literal reading of Genesis, nor has he ever made reference to teaching “creation science” in schools. A member of the prestigious secular French Académie des Sciences Morales et Politiques (inducted in 1993 along with then-Czech President Vaclav Havel as one of only 12 foreign nationals), Pope Benedict has no desire to launch a crusade against modern science.

Nor is Benedict XVI really an advocate of “intelligent design” in the American sense, since intelligent design theorists typically assert that data from biology and other empirical sciences, by itself, requires the hypothesis of a designer. Benedict may have some sympathy for this view; he has questioned the evidence for “macro-evolution,” meaning the transition from one species to another on the basis of random mutation and natural selection.

Ultimately, however, he sees this as a debate for scientists to resolve.

His concern cuts deeper, to what he sees as the tendency to convert evolution into “a universal theory concerning all reality,” improperly transposing Darwin from the scientific to the philosophical realm. Such a worldview, Benedict believes, excludes God, and therefore excludes rationality, as the basis of existence. In contrast, the pope insists upon the fundamental conviction of Christian faith: “In principio erat Verbum – at the beginning of all things stands the creative power of reason.”

Benedict acknowledges that this question “can no longer be decided by arguments from natural science.”

Beyond these essentials, one can outline the pope’s thinking in terms of four concepts.

- Whatever the findings of the natural sciences, they will not contradict Christian faith, since ultimately the truth is one.

This confidence is expressed in Ratzinger’s 1990 book, In the Beginning: A Catholic Understanding of the Story of Creation and the Fall.

“What response shall we make to this view [evolution]?” he asked. “It is the affair of the natural sciences to explain how the tree of life in particular continues to grow, and how new branches shoot out from it. This is not a matter for faith.… More reflective spirits have long been aware that there is no either-or here. We cannot say: ‘creation or evolution,’ inasmuch as these two things respond to two different realities.… The theory of evolution seeks to understand and describe biological developments. But in so doing it cannot explain where the ‘project’ of human persons comes from, nor their inner origin, nor their particular nature. To that extent we are faced here with two complementary -- rather than mutually exclusive – realities.”

- As a scientific matter, the evidence for “micro-evolution” seems beyond doubt; the case for “macro-evolution” is less persuasive.

“Micro-evolution” refers to developmental changes within a species, while “macro-evolution” is the transition from one species to another on the basis of mutation and selection. Some critics of evolution concede the former but dispute the latter, and Ratzinger has voiced support for this view.

His comments come in a Nov. 27, 1999, lecture delivered at the Sorbonne titled “The Truth of Christianity,” published in his 2003 book Truth and Tolerance.

“No one will be able to cast serious doubt upon the scientific evidence for micro-evolutionary processes,” he wrote. “R. Junker and S. Scherer, in their ‘critical reader’ on evolution, have this to say: ‘Many examples of such developmental steps [micro-evolutionary processes] are known to us from natural processes of variation and development. The research done on them by evolutionary biologists produced significant knowledge of the adaptive capacity of living systems, which seems marvelous.’… The problem emerges at the point of transition from micro- to macro-evolution, on which point Szathmáry and Maynard Smith, both convinced supporters of an all-embracing theory of evolution, nonetheless declare that: ‘There is no theoretical basis for believing that evolutionary lines become more complex with time; and there is also no empirical evidence that this happens.’ ”

(Ratzinger here refers to the argument, often made by intelligent design theorists, that organic life reveals an “irreducible complexity” that cannot be ...