How high is the price we would pay for justice?

A sense of justice and injustice is an evolved moral emotion to signal to others that if exchanges are not fair there will be a price to pay. In the Ultimatum Game, in which one person is given a sum of money to divide with another person — with the stipulation that if the offer is accepted both keep the money, but if the offer is rejected no one gets any money — offers less than 30 percent of the sum are typically rejected. That is, we are willing to pay 30 percent to punish an offender. This is called moralistic punishment.

A number of studies have found a small but significant correlation between the early-life use of antibiotics and the later development of inflammatory disorders, including asthma, inflammatory bowel disease and, more recently, colorectal cancer and childhood obesity. One explanation for this association might be that sickly people take more antibiotics. Antibiotics are not the cause, in other words, but the result of preexisting ill health.