The Neuroscience of Our Moral Smorgasbord

Continuing the discussion I posted about earlier, Conor Clarke has responded to Greg Mankiw’s argument about the supposed utilitarian commitment to policies like the taxation of height.  Conor takes a different strategy in defending the broader utilitarian project than I did.  He appeals to the implications of some well-trod ethical thought experiments, like the trolley problem and transplant case:

Consider everyone’s favorite hypothetical from ethics 101: A runaway train is barreling down the tracks toward five workers, unaware that they’re in for a grisly demise. You are standing on a bluff overlooking the scene, in front of a magic lever that can divert the train to a separate track on which there is a lone worker. Do you pull the switch?

It seems intuitively obvious to me, and I think intuitively obvious to most people, that you should pull the switch. But for me that intuition does not hold across all cases with similar stakes. Switch the scene to a hospital emergency room in which you are the surgeon. You have five patients desperately in need of organ transplants. In walks a healthy person. Do you whack him over the head with a mallet and harvest his organs to save the other five? Maybe readers of the Atlantic aren’t so cowardly, but I wouldn’t!

But I don’t really have a good explanation for why I wouldn’t, except that intuition tells me I don’t want to live in a world where doctors can whack me over the head and steal my liver and lungs in the name of the greater good.

I do!  Well, Joshua Greene does, and having worked in his lab I’m going to reference his work.  Greene is a professor at Harvard who studies the neural basis of moral judgment using exactly the sort of dilemmas Conor discusses.  By having subjects respond to these questions while undergoing fMRI imaging, he’s found that the brain contains two broad networks that respond differently to moral dilemmas depending on situational elements of the dilemma.  One network is in the prefrontal and parietal coritices, and it is statistically indistinguishable from the brain areas responsible for the completion of a working-memory task that carries no moral implications.  The second is in the limbic system and associated areas of paralimbic cortex, which are structures associated with emotional or affective processing.

Activation in the first network is associated with paradigmatically utilitarian judgment–so, in the trolley case, the decision that it is morally appropriate to intervene by pulling the switch and sacrificing the solitary workman to save the other five.  The second network, in contrast, is associated with a rejection of utilitarian principles–Conor’s “moral intuition” that it would be wrong to sacrifice the innocent man in the emergency room for his organs.

The thought is that we evolved a set of moral intuitions as we transitioned from great apes to homo sapiens (Frans de Waal has done a lot of work identifying primitive moral behavior in chimps and other primates) that manifest in strong emotional reactions to situations like the transplant case.  As the neocortex expanded throughout early human evolution, we gained the ability to think abstractly and reason in a consequentialist manner.  Thus, we can appeal to utilitarian principles, but only in cases that are abstract enough that the slower prefrontal-parietal system can produce a judgment before the faster limbic system.

What features of a dilemma evoke a stronger response in the intuitive system? That question is the basis of an ongoing project, but there are a few ideas.  Consider a parallel case to the trolley problem, known as the “footbridge” case.  Here you are again faced with an out-of-control trolley bearing down on five workers, but instead of a switch and a side track you are standing on a footbridge over the rails next to a large workman.  If you push the man off, his mass will stop the trolley and save four lives.  Even though this dilemma is quite similar to the standard trolley case, most people say it’s not morally permissible to take action, and the fMRI data reveal that it produces a stronger response in the limbic system.

The prevailing theory for why we react differently to these dilemmas holds that contemplating the act of physically pushing the man in the footbridge case fits into the limited vocabulary of the intuitive system and evokes a response, while the mechanical, removed action of pulling a switch and moving a train track does not.  The footbridge case is, in Greene’s taxonomy, a “personal dilemma.”  Likewise for the transplant case.  The invasive, bloody action involved there arouses our moral emotions in a way that other utilitarian decisions might not.

Deciding to implement a height tax, of course, carries somewhat less weighty implications than are at play in these hypothetical scenarios, but it would tap into our intuitive sense of fairness that would overwhelm our ability to reason like a detached economist.  Mankiw is right that a political philosophy itself should not be a smorgasbord. But most people’s moral judgments are not based on a complete philosophy.  They’re the product of our biology, often inconsistent, but nevertheless powerful and deserving of consideration.