 Bowles cites research by Ernst Fehr and others establishing that behavioral experiments modeling the voluntary provision of public goods show that "substantial fractions of most populations adhere to moral rules, willingly give to others, and punish those who offend standards of appropriate behavior, even at a cost to themselves and with no expectation of material reward".Diego Rivera's mural of factory workers at Ford's River Rouge assembly plant shows that according to Bowles organizations motivate members "by appealing to other-regarding motives such as the desire to do a good job and a sense of reciprocal obligations among members of a firm".In most cases, "[i]ncentives undermine ethical motives" as they "may frame a decision problem and thereby suggest self-interest as appropriate behavior".