What is the relationship between the size of brain area devoted to a body part and that body part?

I believe that the answer to the question given above is that the size of brain are is defined on how strain or how used is that specific body part.

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The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.