The Science of Morality

There is a trolley hurtling on a track towards five people. On an alternate track, another man is standing. You can pull a switch and cause the trolley to switch to the alternate track and kill the other man, saving five people. What do you do?

Traditionally, the study of morality has been the province of philosophers, but questions like these are increasingly being used in the science lab. Many scientists are now convinced that all phenomena related to human behavior, including morality, are at some level rooted in the physical processes of the brain. Primatologists offer clues about the evolutionary basis of morality through studies of ape social dynamics1; anthropologists collect lists of moral taboos and features universal to every culture ever studied2; cognitive neuroscientists seek the neural correlates of morality3.

Much of the neuroscientific research on morality has been done through functional magnetic resonance imaging (fMRI) studies. fMRI is a piece of technology responsible for the brain scan studies that have become increasingly prominent in recent years, especially as their results are splashed across the front pages of newspapers and online news sites. In a typical fMRI study, participants will be asked to answer questions involving moral judgments while recording metabolic activity of different areas of the brains. Change in metabolic activity is roughly correlated with neuronal activity in a particular area.* fMRI’s greatest successes have been in determining which brain areas are active during particular mental processes.5

Studies like these have also been useful in illuminating the processes that lead to moral decision-making and localizing the areas involved in these processes. Most brain areas are not involved in just one particular function. Usually, multiple and varying combinations of brain areas show activation during many different processes. Because of this, and because of the ill-defined nature of a concept like “morality,” approaches to studying it tend to be roundabout, with researchers investigating, for example, differences between brain activation in psychopaths versus non-psychopaths, the result of brain lesions on moral judgments, and the role of emotion in morality.

One such example is that the answer that a person gives to the trolley question is influenced by whether or not he or she has brain damage, in particular a lesion in the ventromedial prefrontal cortex (VMPFC), which is generally involved in decision-making. Subjects with VMPFC lesions strongly prefer to make the utilitarian choice to kill the man and save the other five.3,4 Meanwhile, selective lesions in the dorsolateral prefrontal cortex (DLPFC) and lateral frontopolar cortex (FPC), which are also involved in the execution of motor tasks and memory, increase the likelihood of making the choice to let the five people die. This is considered the “emotional” choice, since it is thought that it involves the negative emotional reaction that accompanies the thought of having to commit murder.

A number of competing hypotheses have arisen concerning the role that emotion plays in morality. One hypothesis states that emotions illuminate our moral judgments, and moral judgments are particularly associated with areas also linked to empathy; another states that emotion and rationality are at war during such judgments6,7,8. Still another theory states that morality is rooted in a set of areas which underlie prosocial judgments, and that the basis of morality is our need to form social bonds. It is generally agreed that there is not a specific part of the brain devoted to morality, and that it would be wrong to say, for example, that any particular area is the “moral center” of the brain. Rather, morality is the result of many different interacting processes and areas of the brain involved in emotion and decision-making.

Because of its implications for law and society, the science of morality has received a great deal of interest in recent years. In fact, neuroscientific evidence has even become admissible in court9, and new findings may even change our understanding of how to approach moral problems. Furthermore, neuroscientists have sometimes appeared in public media to use their research to promote their own political beliefs.  For these reasons, it is important to understand the great successes of the scientific community in illuminating the evolutionary, psychological, and physiological basis of moral decisions, but at the same time to understand the field’s contentious arguments and methodological failures. In future, I hope to discuss some of the more famous studies produced in the field, as well as the public response to them, and the implications for the way our society thinks about morality.


* More specifically, fMRI measures the BOLD signal, or blood-oxygen-level-dependent signal. Upon contact with radio waves, the dephasing of protons aligned by an external magnetic field is read by the MRI machine. The BOLD signal arises from the different responses of oxygen-poor and oxygen-rich hemoglobin under these conditions. The signal is correlated with the local field potential or LFP, which seems to reflect the amount of dendritic input going to a certain area, rather than the actual firing rates of the neurons involved.  These changes are then quantified per voxel, which can be described as a 3-dimensional pixel that makes up the 3-D brain space that fMRI is scanning. A voxel may contain thousands or tens of thousands of neurons. The statistical methods and assumptions used to interpret fMRI data are still in contention, although the technology has become widespread in scientific laboratories.


  1. Jessica C. Flack and Frans B. M. de Waal, ” ‘Any animal whatever’. Darwinian building blocks of morality in monkeys and apes,” Journal of Consciousness Studies 7 (2000): 1-29.
  2. Donald E. Brown, Human universals (Philadelphia: Temple University Press, 1991).
  3. Jorge Moll and Ricardo de Oliveira-Souza, “Moral judgments, emotions and the utilitarian brain,”Trends in Cognitive Sciences 11 (2007): 319-321.
  4. Michael Koenigs et al., “Damage to the prefrontal cortex increases utilitarian moral judgements,” Nature 446 (2007): 908-911.
  5. Nikos K. Logothetis et al., “Neurophysiological investigation of the basis of the fMRI signal.” Nature  412 (2001): 150-157.
  6. Jean Decety et al., “The contribution of emotion and cognition to moral sensitivity: a neurodevelopmental study,” Cerebral Cortex 22 (2012): 209-220.
  7. Joshua D. Greene et al., “An fMRI Investigation of Emotional Engagement in Moral Judgment,” Science 293 (2001): 2105-2108.
  8. Jorge Moll et al., “The neural basis of human moral cognition,” Nature Reviews Neuroscience 6 (2005):799-809.
  9. Lizzie Buchen, “Science in court: Arrested development,” Nature 484 (2012): 304-306.
  10. Image credit (Creative Commons): Kenny Stoltz, “This is my brain,” Flickr. Last modified November 23, 2006.

Lucy Li is a third-year student at the University of Chicago majoring in biology. Follow The Triple Helix Online on Twitter and join us on Facebook.


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