Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum of Natural History in New York. In 1996, Gould was hired as the Vincent Astor Visiting Research Professor of Biology at New York University, after which he divided his time teaching between there and Harvard. Gould's most significant contribution to evolutionary biology was the theory of punctuated equilibrium developed with Niles Eldredge in 1972. The theory proposes that most evolution is characterized by long periods of evolutionary stability, infrequently punctuated by swift periods of branching speciation. The theory was contrasted against phyletic gradualism, the popular idea that evolutionary change is marked by a pattern of smooth and continuous change in the fossil record. Most of Gould's empirical research was based on the land snail genera Poecilozonites and Cerion. He also made important contributions to evolutionary developmental biology, receiving broad professional recognition for his book Ontogeny and Phylogeny.[5] In evolutionary theory he opposed strict selectionism, sociobiology as applied to humans, and evolutionary psychology. He campaigned against creationism and proposed that science and religion should be considered two distinct fields (or "non-overlapping magisteria") whose authorities do not overlap. Gould was known by the general public mainly for his 300 popular essays in Natural History magazine, and his numerous books written for both the specialist and non-specialist. In April 2000, the US Library of Congress named him a "Living Legend"