This thesis explores Nicholas Agar’s criticism of radical enhancement in his book Humanity’s End. He claims that enhancing the human body in a way that goes beyond the limitations of human biology, will turn us into something that cannot properly be called humans, and therefore alienate us from ourselves, from our loved ones and from important experiences that have great value to humans. I argue that there are some serious flaws in Agar’s argument: first that his argument is circular; that fact that you are human doesn’t require you to preserve that state of existence. Secondly, we don’t have a clear definition of what it means to be human in the first place. For example, we can imagine a person being enhanced with various cybernetic implants and prostheses, but still being genetically identical with humans. If we don’t clearly know what it means to be human, how do we know whether this is worse or better than being, say, a posthuman? There appears however to be a way for Agar to accept enhancement if they happen bit by bit, over many generations, which seems reasonable, granted that it is easier to control the direction of where human progression will go. Agar is close to endorsing a eugenics program, as modeled by Julian Huxley, to gradually improve humanity over several generations.