What are the origins and purpose of the "rubber" on the pitcher's mound?

darn I thought this was going to be a sexual question.

I’m not sure of the origins but this is what I have always heard.

A pitcher will push off the rubber with his foot in order to gain velocity toward home plate when pitching.

it is a case of closing the barn door after the cows have gone. The mound clearly shows that the field is already knocked up.

The origin is a partially buried (for stability) marker so that the pitchers maintain a standard distance from the home plate (60’ 6” from the back corner of home plate to the front edge of the pitcher’s plate in High School, College and professional baseball). The distance varies in softball, depending upon the type of softball (fast-pitch, slow-pitch, etc.) and the rules of the various leagues.