Organic Evolution

Organic evolution is defined by the development of organisms from simple and homogeneous to complex and heterogeneous forms.It is a continuous and never-ending process  from the time life appeared  on the earth millions of years ago.A multitude of life forms appeared  in the geological past  and many species  became extinct some of them terminally due to changes in the environment.Studies on fossils and living animals and plants bear out a continuous development in which each stage grows out of the one before.It seems as though organic evolution unfolds forces that have been always defined ever since life first appeared.In physical anthropology the concept of evolution is traced from the first  appearance of primitive  organisms  through stages of development of many species ending with the appearance of Homo Sapiens.

Jean Baptiste Lamarck held that acquired characteristics could be inherited and that individuals who in their lifetime developed characteristics helpful for survival would pass on the characteristics to future generations.Thereby the physical make up of the species will change.He explained the long neck of giraffe as the result of successive generations of giraffes stretching their necks to reach leaves at high levels  in trees.Erasmus Darwin  a contemporary of Lamarck also held the view that acquired characteristics were inherited and explained evolutionary changes in life forms.Neither Lamarck nor later biologists produced any evidence in support of inheritance or acquired characteristics.Charles Lyell in his Principles of Geology rejected the idea of evolution of species of life.According to him the natural law of evolution was applicable to the earth but not to animals and plants.Charles Darwin based his study of evolution by natural selection on the findings done on plants,fossils and variety of animals.Alfred Russel Wallace also shared his theory of natural selection with Darwin.Darwin gave a comprehensive and well documented  explanation in support.He pointed out that species is composed  of a great variety of individuals and in them some of them adapted to their environment than others.Changes in a species can be expected to take place when the environment changes or if some members move into a new environment.