There are three main theories of evolution: special creation, Lamarckism, and Darwinism. Special creation believes organisms were created in their current form with no evolution. Lamarckism proposes that acquired traits can be inherited, such as giraffes developing long necks, but it was rejected as traits are not inherited. Darwinism theorizes that populations vary, there is a struggle for existence, and natural selection leads to the survival of the fittest whose variations are inherited, resulting in evolution and speciation over generations.