My brain made me do it

Two individuals, in separate incidents, stab another person to death. One individual is found guilty and sentenced by a judge to 20 years in prison. The other is found guilty and sentenced to seven years in prison. Is this fair?

According to the latest scientific evidence: yes - in certain circumstances.

And one of those circumstances is if the offender is a teenager. This is because teenagers' brains have been shown to lack the kind of impulse control that adults have (or are supposed to have).

The suggestion is that even if a teenager succumbs to an impulse to cause harm this may not necessarily reflect on their character later in life. As put by US Supreme Court Justice Anthony Kennedy, writing for the 5-4 majority that outlawed the execution of anyone under 18 in 2005:

It is less supportable to conclude that even a heinous crime committed by a juvenile is evidence of irretrievably depraved character.

Yet it has also been suggested that the lack of impulse control in teenagers, particularly males, including some up to their mid-20s, may be an evolutionary adaptation. This lack of impulse control might manifest in a willingness to engage in more risky behaviour. This might be beneficial to young bachelor males who are competing for resources and, ultimately, mates.

Risk taking - as anyone who has spent any appreciable time in Vegas will tell you - can result in big wins, but often at the expense of many losses. Abstracted across a population, the big winners are the males who end up with multiple offspring at the expense of males who have few or no offspring. (The same is true on the stockmarket - which is why it's not prudent to follow the advice of the broker with the highest returns. Chances are he or she [more likely a 'he' because of the risk taking] has gone risky and struck it lucky. He/she may not be so lucky in future.)

The question is: just because an individual's impulse control is hampered by an evolutionary relic, does that excuse them from immoral behaviour?

This starts to touch on problems with the naturalistic fallacy (as commonly conceived), i.e. that you can't derive an ought from an is. Were you able to do so, then if something is natural, then it can be conceived as being good. And murderous impulses might be natural, but I'm sure we'd be reluctant to accept them as good.

I'm not sure what the answer to this issue is - but I do think the answer can't come purely from reason. Even if we reason that an individual is unlikely to commit another crime in the future, it still remains that we have overpowering impulses towards retributionism and punishing moral transgressions - not necessarily for any reasonably or utilitarian ends, but just because we're outraged. Just listen to the pleas for 'justice' from the families of murdered individuals. Reasonable they may not be, but it's hard not to feel the pathos of their pleas.

Nature may not be necessarily good. But nature certainly influences good. And that's only going to be a continuing problem for courts and the legal system as a whole as science reveals more facts about our nature.