Concepts of Evolutionary Theory and Biogeography ーThrough a Comparison of Darwin and Wallaceー

The existence of a global British ethos from the 18th century to the 19th century such as the development of the philosophy of the European Enlightenment, the Industrial Revolution and colonial expansion was established as the social background for the establishment of evolutionary biogeography. Darwin has denied creationism and catastrophic theory to develop uniformitarian theory and gradualism together with confirming global biodiversity. As a result, the surprising diversity of the species all over the world and the fact that species of living creature differ according to location even if the basic environment is the same became evident. This does not conform with creationism whereby species must have been created in perfect compatibility with the environment. Also catastrophic theory was considered to have been refuted by Lyell’s uniformitarian theory. Whilst creationism was being refuted 19th century, the elucidation of the process of dispersal and divergence from a common progenitor in one original place was required in order to establish the successive temporal and spatial evolution of living things. The direction of research into this kind of biogeography of the distribution of living things concurred with the biological paradigm shift that was the proposal of evolutionary theory. With these circumstances as a background, Darwin conceived the theory of evolution from the consideration of the distribution of living things. Initially, Darwin thought that the individual variations of living things were caused by exposure to a new environment. “Geographical isolation” was taken to be important as a principal component of this speciation and research into the migration and diffusion of living things was conducted. However Darwin thought that if there is sufficient time, and physical and ecological barriers are removed then a species will spread throughout the world. Darwin initially considered the impact of a geographical barrier with regards to speciation however he came to stress the mechanism of fortuitous transport as the cause of this diffusion and geographical distribution. Furthermore through carrying out observations and research into particles after his return to Great Britain, Darwin understood the large quantity of variation in the natural world even in the same environment. In short, the variation of living things occurs even without geographical or geological change. Meanwhile in contrast to Darwin, Wallace spent his life considering the relationship between evolution and geographical distribution in his theory, and continued to explain the influence changes in the geographical factors of the environment have on the distribution of living things and evolution. He stressed changes in the Earth’s crust such as upheaval and subsidence as impacts had on the distribution and isolation of living things. This is also reflected in the differences between Darwin’s and Wallace’s theories of evolution. In Darwin’s Origin of Species, the main constituent of evolution is very much the bion. An individual in a species occupies various positions and locations in connecting with the ecosystem, the individual proactively adapts to those conditions and variation is produced. At length, the variation of each individual accumulates on average, the whole species diverges and new species are formed. In contrast, Wallace’s evolutionary theory states that the unit of evolution is variation; only variations to adapt to changes in environmental conditions such as ensuring a food supply occur ; and these evolve into a new independent species. This is to say, Darwin’s theory of evolution recognised the diversity of the random changes of many individuals. Thereafter, Darwin’s theory of evolution was introduced to Germany by Haeckel and started to spread. Biogeographical and ecological theory came to be introduced to geography by Ratzel who was strongly influenced by Haeckel. However Haeckel’s concept differed to that of Darwin in that it depended on orthogenesis. Also although the biology of Haeckel broke down the concept of natural theology in Germany, it was on the other hand, an organic monism that was strongly influenced by the ideology of romanticism. The geography of Ratzel, which received this kind of ideology from Haeckel, can be thought to be inclined towards a holistic theory of social organismdepartmental bulletin pape