"If different humans have different natures, and even individual humans have different natures at different times, then how can there be a single human nature?"
"How long is a banana?"
"I don't know—about seven inches?"
"Are all banana's seven inches long then?"
"No. Some are longer than others."
"And is every individual banana the same length for it's entire life on the stem?"
"It's smaller when it starts out, and then gets longer as it grows, I would guess."
"So then it makes no sense to talk of the length of bananas?"
"Well, I guess not."
"Don't give up so easily. Defend yourself. Were you talking nonsense when you said, 'about seven inches'?"
"I was just being general I guess. Bananas vary in length, but there's still..."
"Banana do what in length?"
"So the length of a banana is not a number, but a..."
"And can a variable take on any value at all?"
"Any value in its domain."
"And would you say that the domain of a banana's length is limited?"
"You don't see many twelve-foot bananas."
"And would you say this domain has a shape?"
"I don't know what you mean by that?"
"Are there certain lengths that are more likely than others?"
"So human nature is a variable, which can only take on certain values, and which tends to concentrate in a certain range!"
"Not bad, but remember our previous discussion. Is human nature a single variable?"
"It's a set of variables."
"Does that answer your original question?"
"Well, actually, no. It doesn't."