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 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 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, |