In Breakfast of Champions, a novel by Kurt Vonnegut, the main character reads a book that convinces him that all other humans are no more than fleshy machines. He believes that he alone is capable of free will. This belief affects his behaviors towards other people and is a way he justifies mistreating some of them. This novel is a silly and vulgar expression of the effects of how we define personhood and humanity.
Unfortunately, Western civilization has seen many similar sorts of stories manifest in real life. Consider how the ways we define humanity and personhood have been used in the past to justify oppression and violence. To what extent should our definitions of 'humanity' and 'person' be inclusive? Consider how such definitions influence our concepts of moral responsibility and morality. Are there non-human persons? Is it conceivable that non-humans may have something like 'humanity'? To what extent is humanity necessary for moral obligations?