are often called theories of blending inheritance. There was, however, no practical and experimental proof for such theories of blending inheritance, and all of these were discarded. For example, the trait of sex never gets blended in the unisexual organisms; such individuals are either males or females. There is no mixing or “blending” of that characteristic. Lamarck’s Theory of Use and Disuse In the early 1800s, Jean-Baptiste Lamarck, a French naturalist , proposed a theory known as the theory of use and disuse. It described how the structure of an organism altered over generations and how environment played an important role in that process. Lamarck proposed that by selective use and disuse of organs, organisms acquired Jean-Baptiste Lamarck

and stretching until neck becomes progressively longer

Keeps stretching neck to reach leaves higher up on tree

Original short-necked ancestor

Lamarck’s theory


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