Charles Darwin's views on religion have been the subject of much interest and dispute. His pivotal work in the development of modern biology and evolution theory played a prominent part in debates about religion and science at the time. In the early 20th century, his contributions became a focus of the creation–evolution controversy in the United States. While Darwin came to heavily dispute the dogmatic prescriptions of the Anglican Church and Christianity in general, later in life he clarified his position as an agnostic in response to a letter from John Fordyce: