What would be the result of erythropoietin overproduction by the kidneys?

The results of erythropoietin overproduction by the kidneys is high hematocrit (too many red blood cells). Erythropoietin is a growth factor that stimulates the production of the red blood cells which are the major cells in the blood and whose main function is to carry oxygen throughout the body. This means if there is an increase in erythropoietin production then there would be an corresponding increase in production of red blood cells. 

Due to the amount of pressure

Probably a behavioral adaptation