Christensen, C. M., Allworth, J., and Dillon, K., How Will You Measure Your Life (New York: HarperCollins, 2012; Kindle edn), ch. 7.

Sun, L., The Fairness Instinct: The Robin Hood Mentality and Our Biological Nature (New York: Prometheus Books, 2013; Kindle edn), and Ridley, M., The Origins of Virtue (London: Penguin, 1996; Kindle edn)