According to biophysicist Cornelius G. Hunter, writing in a recent article appearing in the journal Religions, Darwin's theory of evolution can best be understood as a sort of "theological research project" (hat tip to Michael Flannery at Evolution News for making me aware of Hunter's article). Such a claim contradicts the standard view that Darwin's theory was founded principally on scientific considerations. Nevertheless, Hunter demonstrates in his article that, in fact, in Darwin's theory, "theological concerns...have primacy over the science. They motivate the development of evolutionary theory, and they control control the interpretation of the empirical evidence and justification of the theory." To prove these assertions, in his article Hunter responds in detail to various arguments that have been made over the years defending Darwin's theory from the charge that the "one long argument" made in his On the Origin of Species is essentially theological rather than scientific in nature.
One example of Darwin's use of theology to support his theory can be found in his insistence that if God had created each species individually, then every biological structure--like a wing or an eye--would exhibit a utilitarian design. In other words, "every detail of structure has been produced for the good of its possessor" (Darwin, On the Origin of Species, as quoted in Hunter). However, Darwin asserts, many biological structures are in fact not useful to their possessors. Therefore, it must follow that these structures are not the work of an all-wise Creator but rather the result of a random process of evolution. In making such an argument, Darwin rejected the view of some natural theologians that God might have created certain biological structures not for reasons of utility, but for "beauty in the eyes of man, or for mere variety" (Darwin, On the Origin of Species, as quoted by Hunter). Note, however, that in asserting that the Creator would have only designed biological structures with their utility in mind, Darwin was making a theological argument, not a scientific one. He was saying, in effect, that God would not have had non-utilitarian reasons for a particular design in biological organisms--which is merely an unproven assumption, not grounded in any compelling evidence.
We might ask why it is important that Darwin's "one long argument" for evolution was primarily theological rather than scientific in nature. It matters, for one thing, because it undermines the common perception that Darwin proved scientifically that evolution is true. It also matters because even today arguments for the truth of evolution are, at their foundation, essentially theological in nature. As Hunter puts it, "theology is epistemologically crucial to evolutionary theory." However, if evolutionary theory is ultimately based on theological assumptions, rather than scientific facts, then it can properly be disputed, rather than be upheld as unassailable truth.
Image of Charles Darwin from Wikimedia Commons