... changes through a long period of time. In the early 1800s, another French naturalist named Lamark, proposed the first complete theory of evolution. He observed through is observations, depending on the extent to which the use of the structure, that an animal's body structure is able to change during its life span. He also noted that organs and muscles, which were used often, tended to become larger and stronger. On the contrary, the organs and muscles, which were used seldom, tended to become smaller and diminish. With these observations, Lamarck concluded that these characteristics were hereditary. Proposed during two decades, the 1930s and 1940s, the synthetic theory involved a group of scientists. The group of scientists included two American biologists, Russian Theodosius and German Ernst Mayr, and the British geneticist and statistician Ronald A. Fisher. Together, they proposed the synthetic theory which combined Darwin's theory of natural selection with the ...

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