Participant evolution is a process of deliberately redesigning the human body and brain using technological means, rather than through the natural processes of mutation and natural selection, with the goal of removing "biological limitations." The idea of participant evolution was first put forward by Manfred E. Clynes and Nathan S. Kline in the 1960s in their article Cyborgs and Space, where they argued that the human species was already on a path of participant evolution. Science fiction writers have speculated what the next stage of such participant evolution will be.