Osborn was a proponent of ''orthogenesis,'' as were many paleontologists up through the middle of the twentieth century. These paleontologists interpreted the fossil record as showing sustained, continuing, unidirectional trends in [[Theory of evolution|evolution]], which they felt required some kind of driving principle in addition to natural selection. As the author of an encyclopedia article on variation and selection put it in 1911, | Osborn was a proponent of ''orthogenesis,'' as were many paleontologists up through the middle of the twentieth century. These paleontologists interpreted the fossil record as showing sustained, continuing, unidirectional trends in [[Theory of evolution|evolution]], which they felt required some kind of driving principle in addition to natural selection. As the author of an encyclopedia article on variation and selection put it in 1911, |