Despite having its roots in ancient Greece, the theory of evolution was first brought to the attention of the scientific world in the nineteenth century. The most thoroughly considered view of evolution was expressed by the French biologist Jean-Baptiste Lamarck, in his Zoological Philosophy (1809). Lamarck thought that all living things were endowed with a vital force that drove them to evolve toward greater complexity. He also thought that organisms could pass on to their offspring traits acquired during their lifetimes. As an example of this line of reasoning, Lamarck suggested that the long neck of the giraffe evolved when a short-necked ancestor took to browsing on the leaves of trees instead of on grass.
This evolutionary model of Lamarck's was invalidated by the discovery of the laws of genetic inheritance. In the middle of the twentieth century, the discovery of the structure of DNA revealed that the nuclei of the cells of living organisms possess very special genetic information, and that this information could not be altered by "acquired traits." In other words, during its lifetime, even though a giraffe managed to make its neck a few centimeters longer by extending its neck to upper branches, this trait would not pass to its offspring. In brief, the Lamarckian view was simply refuted by scientific findings, and went down in history as a flawed assumption.
However, the evolutionary theory formulated by another natural scientist who lived a couple of generations after Lamarck proved to be more influential. This natural scientist was Charles Robert Darwin, and the theory he formulated is known as "Darwinism."