Because I am human. I am complex series of atoms: infinitesimal as individuals, yet capable of sentience as a whole. I am constricted to the laws of physics. I am an object, I take up space in the universe; no amount of intellect can stop my body from being absorbed into it. So physically, I represent humanity because I share the same fate as everyone else; dust to dust, as it were.
Beyond that:
I have faith, yet am Atheist. I am a conglomerate of ethnicities, yet am only one nationality. I love, play, hate and anger; I lust, become sad, fear and feel pride. I am arrogant yet insecure. I am human and represent humanity – if only because I experience the same wondrous range of emotions as everyone else in the world. No other object in this room can claim that.