Lamarckism:

—Jean Baptiste Lamarck published his theory of evolution in 1809.

—He presented a mechanism to explain how specific adaptations evolve.

—“Lamarck argued that  those parts of the body used extensively to cope with the environment become larger and stronger”

Lamarck also argued that “those parts that are not in use  deteriorate”

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—Example:

—Blacksmith developing bigger in the arm that works the hammer.

Inheritance of acquired characteristics:

—this idea suggests that:

—The modifications evolved in an organism to cope with environment  pass on to next generation e.g. the long neck of giraffe ,Lamarck reasoned ,evolved gradually as a cumulative product of a great many generations of ancestors.

Modern theory:

— but the recent research reveals that acquired characteristics cannot be inherited.

 so this idea doesn’t support the modern evolution so far.