The process of speciation, studied by biologists for centuries, is difficult to explain. Speciation is the process of forming a new species. Charles Darwin is one of the most famous people for studying different species and how natural selection has affected evolution; however, he never explained how one species gives rise to another. We know that there are theories about how speciation occurs. The four patterns of speciation are allopatric, sympatric, peripatric and parapatric speciation. In speciation, two factors must occur. The first is that populations diverge. The second is that the populations remained isolated. The roles of mutation and natural selection are important in speciation. Thus, to describe the role of natural selection in the speciation process, a simple definition of what natural selection is must be given. Natural selection is the process by which organisms that are better adapted to their environment tend to survive and are able to reproduce. Natural selection is one of the fundamental mechanisms of evolution. If you have variation, differential reproduction and heredity, you will result in evolution by natural selection. In Darwin's theory of natural selection, the example of giraffes is given. In this example of giraffes, Darwin suggests that the variation was the result of pre-existing genetic differences between giraffes. While this other biologist Jean-Baptiste Lamarck believed that evolution occurred through the inheritance of acquired characteristics. He believed that the giraffe's ancestor elongated its neck by stretching to reach the leaves of trees, then passed the change on to its offspring. However, Darwin believed that some giraffes were just born with longer necks due to genetic differences. In parapatric speciation, there is no specific extrinsic barrier to gene flow. The population is continuous, but nevertheless, it does not mate randomly. Individuals are more likely to mate with their geographic neighbors than with individuals located in a different part of the population range. Peripatric speciation is similar to allopatric speciation except for size. In peripatric speciation, a small population is isolated at the edge of a larger population. Note that in peripatric speciation, small population size would make full-blown speciation a more likely result of geographic isolation, because genetic drift acts more quickly in small populations. Genetic drift would cause rapid genetic change in the small population. This genetic change could lead to speciation.