We’re not good at large numbers. Our brains are adapted to living in groups of perhaps 150 individuals. City living is a very recent innovation, and our psychological mechanisms struggle to cope with it. One way in which we may go astray is through the misapplication of heuristics that worked well for our ancestors, but which misfire in very large groups. Suppose you learn that there is a person in your group prone to violence without provocation. If you live in a group of 150 individuals, you need to be on high alert: your paths will cross. But if you live in a city of 5 million people, you really shouldn’t worry (unless you have some reason to think the violent individual lives in your street). In fact, on learning that there is such an individual you will probably feel more anxiety than you should – not as much as you would if you knew your paths would cross, but more than you rationally ought to.In general, we are bad at understanding low-probability risks. One result is that we attend far more to risks that are novel or which stem from deliberate actions by others than those that come from disease or which we are familiar with. We worry far more about Ebola than the flu, though the flu is likely to kill far more people and carries a higher risk of a pandemic (in Africa, malaria kills many more people than does Ebola). We worry much more about terrorism than about food poisoning, though the risk of dying from food poisoning is much greater than the risk of dying from terrorism.
The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.