Jean Baptiste Lamarck
The French Naturalist Jean Baptiste Lamarck pronounced thefirst comprehensive theory of evolution in the beginnings of the 19th century. His theory, the theory of acquired characteristics, had three parts and is as follows:
1) Theory of need- the production of a new organ or part of a plant or animal results from a need
2) Theory of use and disuse- organs remain active as long as they are being used but disappear gradually with disuse
3) Theory of inheritance- all that has been acquired or changed in the structure of individuals during their life is transmitted by heredity to the next generation.
He believed evolution took place over a very long period of time.
Lamarck also divided animal life into the categories of vertebrates and invertebrates.
The contributions of Lamarck are worth considering, not because he successfully accounted for the process of evolution, since his ideas have never been supported by evidence, but because he at least provided a plausible theory for the multiplicity of forms of living things. His work attempted to change how people of the time thought about themselves and their origins by challenging the popular belief in creationism.
Lamarck's real contribution to scientific thinking, however, lies in his division of animal life into the vertebrate and invertebrate categories. However scientific understanding was hardly changed by his incorrect hypothesis about evolution as few truly believed in his theory.
Lamarck did have an impact on future advances as some of those, who were doubtful about his ideas, started doing their own research. For example, in 1870, an English Biologist, Weismann, proved that the transfer of acquired characteristics to other generations was impossible showing Lamarck's theory to be incorrect.
His work also helped make Darwin's ideas more acceptable by exposing people to non-religion based explanations on the origin of life.