"The hypothalamus and limbic system ... flood our consciousness with all the emotions – hate, love, guilt, fear, and others – that are consulted by ethical philosophers who wish to intuit the standards of good and evil. What, we are then compelled to ask, made the hypothalamus and the limbic system? They evolved by natural selection. That simple biological statement must be pursued to explain ethics."

'Sure, that's what I mean,' Doc Daneeka said. 'A little grease is what makes this world go round. One hand washes the other. Know what I mean? You scratch my back, I'll scratch yours.'
Yossarian knew what he meant.
'That's not what I meant,' Doc Daneeka said, as Yossarian began scratching his back. 'I'm talking about co-operation. Favors. You do a favor for me, I'll do one for you. Get it?'
'Do one for me,' Yossarian requested.
'Not a chance,' Doc Daneeka answered.