Who said "This is what it means to be human."?

This quote is attributed to Marty McFly.

This is what it means to be human. - Marty McFly

"This is what it means to be human."

Marty McFly

"This is heavy."

"There's that word again, 'heavy.' Is there something wrong with the Earth's gravitational pull?"

"I'm your density. I mean, your destiny."

"You're my best friend, and I care about you, but don't ask me to do this."