Abstract
According to the neo-Darwinian interpretation of evolution, all living forms have arisen from a single form of life by slow gradual changes. Thus, the time between the origin of life and the abrupt appearance in the fossil record of the many complex invertebrate forms of life is now estimated to have been nearly three billion years. The time required for one of these invertebrates to evolve into the vertebrates, or fishes, has been estimated at about 100 million years, and it is believed that the evolution of the fish into an amphibian required about 30 million years. The essence of the neo-Darwinian view is the slow gradual evolution of one plant or animal into another by the gradual accumulation of micromutations through natural selection of favored variants.