An Eye for An Eye

Biblical justice... does it work?

Not if you follow the science. Here is a nice summary by Satoshi Kanazawa in his Psychology Today blog The Scientific Fundamentalist:

In the United States, the death penalty is a sensitive political issue. Many of the hotly contested issues are moral and philosophical in nature, so they are outside the purview of science. At least one issue, however, is purely scientific, the question of whether the death penalty has the intended deterrent effect. Does the knowledge and prospect of execution deter potential future murderers from committing the crime?

While the political and public debate continues, the preponderance of scientific evidence, both from cross-sectional (comparing states with and without the death penalty) and longitudinal (examining the same states before and after the introduction of death penalty) studies seem to indicate that the death penalty does not have the intended deterrence effect. It does not appear that there are fewer murders, at different places and times, as a result of the availability of the death penalty as a possible punishment for convicted murderers.

Why is this? There is no greater criminal punishment than the death penalty. Why does it not deter murder?

The fact that the death penalty does not deter murder is a puzzle for the social scientists, especially rational-choice microeconomists. From a microeconomic perspective, each actor makes a deliberate and careful cost-benefit analysis before making any decision. The lack of deterrence effect of the death penalty is therefore puzzling from this perspective, unless the probability of detection, arrest, prosecution, and conviction is infinitesimal. No matter what the actors want, they cannot pursue and consume it if they are dead. So, from the microeconomic perspective, there should be very few occasions where it makes sense for rational actors to decide to commit murder at a realistic risk of execution.
From an evolutionary psychological perspective, however, the lack of deterrence effect of the death penalty is not a puzzle at all. First, contrary to microeconomics, murder in most cases is not a deliberately planned action. It usually begins with “trivial altercations,” where one man insults another by questioning his honor, status, and reputation. They begin a fight, which escalates to the point where one man ends up dead. The death penalty does not deter murder because there is very little forethought and cost-benefit analysis involved in it. Men usually do not consciously decide to commit murder. The death penalty may deter other types of criminals, who make a deliberate decision to commit a crime, or fictional murderers on Columbo, but not most real-life murderers. Most real-life murderers are not like those we see on Columbo and other whodunit shows. For one thing, they are very seldom highly intelligent and successful men and women.

Second, and more importantly, once again contrary to microeconomics, there is something worse than death. From an evolutionary psychological perspective, life – and everything in it – is a means to the ultimate end of reproductive success. So death is not the worst thing; complete reproductive failure is. If some men face a very dim reproductive prospect and a distinct possibility of ending their lives as total reproductive losers, it makes perfect evolutionary sense for them to be violent toward other men, in an attempt to eliminate them as intrasexual rivals for mates by killing or maiming them. It also makes perfect evolutionary sense for men who cannot gain legitimate reproductive access to women to attempt to do so illegitimately through forcible rape. This is why most criminals – especially murderers and rapists – are poor, uneducated men of few means and low social status who face very grim reproductive prospects.

I generally find Kanazawa a little to simplistic and "fundamentalist" for my taste, but he does a good job of popularizing ideas from the field of evolutionary psychology.