Complex sentence: Charles Darwin, as a student of theology, was required to read it when he did his undergraduate studies at Christ's College, but it was Paley's "Natural Theology" that most impressed Darwin even though it was not a set book for undergraduates.
Split into simpler sentences: Charles Darwin, as a student of theology, was required to read it when he did his undergraduate studies at Christ's College. But it was Paley's "Natural Theology" that most impressed Darwin, even though it was not a set book for undergraduates.