the results in other plants. Where Darwin's theories suggested a mechanism for improvement of species over generations, Mendel's observations provided explanation for how a new species itself could emerge. Though Darwin and Mendel never collaborated, they were aware of each other's work (Darwin read a paper by Wilhelm Olbers Focke which extensively referenced Mendel). Bill Bryson writes that "without realizing it, Darwin and Mendel laid the groundwork for all of life sciences in the twentieth century. Darwin saw that all living things are connected, that ultimately they trace their ancestry to a single, common source; Mendel's work provided the mechanism to explain how that could happen". Biologist J. B. S. Haldane and others brought together the principles of Mendelian inheritance with Darwinian principles of evolution to form the field of genetics known as the modern evolutionary synthesis. Changing awareness of the age of the Earth and fossil records helped in the development of evolutionary theory. The work of the Danish scientist Nicolas Steno (1638-1686), who converted to Catholicism and became a bishop, helped establish the science of geology, leading to modern scientific measurements of the age of the Earth. Early reaction to Charles Darwin's theories Catholic concern about evolution has always been very largely concerned with the implications of evolutionary theory for the origin of the human species; even by 1859, a literal reading of the Book of Genesis had long been undermined by developments in geology and other fields. No high-level Church pronouncement has ever attacked head-on the theory of evolution as applied to non-human species although a bishop of the church did excommunicate Gregorio Chil y Naranjo for his scientific work defending Darwin and Lamarck. Even before the development of modern scientific method, Catholic theology had allowed for biblical text to be read as allegorical, rather than literal, where it appeared to contradict that which could be established by science or reason. Thus Catholicism has been able to refine its understanding of scripture in light of scientific discovery. Among the early Church Fathers there was debate over whether God created the world in six days, as Clement of Alexandria taught, or in a single moment as held by Augustine, and a literal interpretation of Genesis was normally taken for granted in the Middle Ages and later, until it was rejected in favour of uniformitarianism (entailing far greater timeframes) by a majority of geologists in the 19th century. However,