There are number of primate and human studies that suggest that we value perceived justice and fairness and just offering positive expected return is not enough.<p>A Theory of Fairness, Competition, and Cooperation
<a href="http:&#x2F;&#x2F;qje.oxfordjournals.org&#x2F;content&#x2F;114&#x2F;3&#x2F;817.short" rel="nofollow">http:&#x2F;&#x2F;qje.oxfordjournals.org&#x2F;content&#x2F;114&#x2F;3&#x2F;817.short</a><p><a href="https:&#x2F;&#x2F;epub.ub.uni-muenchen.de&#x2F;726&#x2F;1&#x2F;Fehr-Schmidt_Handbook_2005-Munichecon.pdf" rel="nofollow">https:&#x2F;&#x2F;epub.ub.uni-muenchen.de&#x2F;726&#x2F;1&#x2F;Fehr-Schmidt_Handbook_...</a><p>Justice- and fairness-related behaviors in nonhuman primates
<a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pmc&#x2F;articles&#x2F;PMC3690609&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pmc&#x2F;articles&#x2F;PMC3690609&#x2F;</a><p>Chimpanzees play the ultimatum game
<a href="http:&#x2F;&#x2F;www.pnas.org&#x2F;content&#x2F;110&#x2F;6&#x2F;2070" rel="nofollow">http:&#x2F;&#x2F;www.pnas.org&#x2F;content&#x2F;110&#x2F;6&#x2F;2070</a>