favoured over natural selection as being more compatible with purpose. Even though the book did not explicitly spell out Darwin's beliefs about human origins, it had dropped a number of hints about human's animal ancestry and quickly became central to the debate, as mental and moral qualities were seen as spiritual aspects of the immaterial soul, and it was believed that animals did not have spiritual qualities. This conflict could be reconciled by supposing there was some supernatural intervention on the path leading to humans, or viewing evolution as a purposeful and progressive ascent to mankind's position at the head of nature. While many conservative theologians accepted evolution, Charles Hodge argued in his 1874 critique "What is Darwinism?" that "Darwinism", defined narrowly as including rejection of design, was atheism though he accepted that Asa Gray did not reject design. Asa Gray responded that this charge misrepresented Darwin's text. By the early 20th century, four noted authors of The Fundamentals were explicitly open to the possibility that God created through evolution, but fundamentalism inspired the American creation–evolution controversy that began in the 1920s. Some conservative Roman Catholic writers and influential Jesuits opposed evolution in the late 19th and early 20th century, but other Catholic writers, starting with Mivart, pointed out that early Church Fathers had not interpreted Genesis literally in this area. The Vatican stated its official position in a 1950 papal encyclical, which held that evolution was not inconsistent with Catholic teaching. Modern influence Various alternative evolutionary mechanisms favoured during "the eclipse of Darwinism" became untenable as more was learned about inheritance and mutation. The full significance of natural selection was at last accepted in the 1930s and 1940s as part of the modern evolutionary synthesis. During that synthesis biologists and statisticians, including R. A. Fisher, Sewall Wright and J. B. S. Haldane, merged Darwinian selection with a statistical understanding of Mendelian genetics. Modern evolutionary theory continues to develop. Darwin's theory of evolution by natural selection, with its tree-like model of branching common descent, has become the unifying theory of the life sciences. The theory explains the diversity of living organisms and their adaptation to the environment. It makes sense of the geological record, biogeography, parallels in embryonic development, biological homologies, vestigiality, cladistics, phylogenetics and other fields, with unrivalled explanatory power; it has also become essential to applied sciences such as medicine and agriculture. Despite the scientific consensus, a religion-based