Does Human Morality Arise from Brain Chemistry?

Does Human Morality Arise from Brain Chemistry?

Some people claim that taking serotonin supplements can improve a person’s health and well being. Recent research by scientists from Harvard and Cambridge suggests that this compound may also improve moral judgment.1

If this discovery turns out to be the case, it raises some very provocative questions.  Is human morality nothing more than biochemical and physiological processes in the brain? If so, does that mean that human beings are merely physical entities with no soul? Or is there a way to understand this work from the perspective of the Christian worldview?

Serotonin’s Impact on Moral Judgment

Work performed prior to this study had suggested that serotonin may have some influence on prosocial behaviors and, consequently, moral decision-making. For example, the serotonin system innervates the areas of the brain shown to be involved in moral judgment and behavior. Other studies have demonstrated that enhanced serotonin function is associated with prosocial behavior while impaired function is associated with aggressive, antisocial behavior.

Based on this earlier research, neuroscientists speculate that serotonin’s positive effect on social interactions is due to one of two mechanisms:

  1. Control of violent impulses and emotional reactions toward others
  2. Increased aversion to doing harm to others

To further evaluate the role of serotonin in prosocial behavior and to distinguish between these two possible mechanisms, researchers from Harvard and Cambridge used the compound citalopram to alter serotonin levels in the brains of volunteers. (Citalopram inhibits the uptake of serotonin in the synapse between nerve cells, thus, prolonging serotonin’s effects during nerve transmission.)

After administering this drug, the volunteers were presented with moral dilemmas and were asked to play the Ultimatum Game.”

When citalopram was administered, volunteers responded to moral dilemmas by seeking to avoid harming others. When playing the game, the test subjects were willing to accept unfair outcomes, if it meant avoiding harm for the other player. The researchers also noticed that those more strongly influenced by serotonin scored higher in empathy than did those who possessed less trait empathy.

On the basis of these results, the researchers conclude that serotonin levels do indeed control moral judgment by influencing the willingness to cause harm to others. These results also seem to imply that our brain physiology and chemistry alone give rise to our moral capacity as human beings. In fact, the researchers went as far as proposing that a boost in serotonin levels may one day serve as a means to treat people with antisocial and aggressive behaviors.

But is it really true that human morality is merely physiological in nature? Is it possible to understand these results from a Christian perspective, one which views human moral capabilities as part of God’s image?

Does Brain Chemistry Define Morality?

Even though the study seems to undermine the Christian worldview, the results of the research do not necessarily support the notion that brain chemistry alone dictates morality. Rather, the study shows that brain chemicals merely modulate morality. The observation that highly empathetic individuals were more responsive to elevated serotonin levels is significant. This observation indicates that “serotonin modulates empathetic response to harm—i.e., by boosting an already-present neural signal—rather than being the source of the empathetic response.” 2

In other words, the brain appears to be hardwired for moral judgment with serotonin influencing the responsiveness of an intrinsically moral brain. This result comports with the Christian worldview and the words Paul wrote in Romans 2:14–15, which teach that all human beings have God’s Law “written on their hearts.” 

A Christian Brain Science Model

If the appropriate mind-body model is adopted, then the Christian framework can readily accommodate the ability to influence moral judgment and behavior through the use of brain chemicals like serotonin or through magnetic fields (see the article I wrote for the e-Zine New Reasons to Believe3).

The model I favor employs a computer hardware/software analogy. Accordingly, the brain is the hardware that manifests human spirituality and the image of God. Meanwhile, the image of God itself is analogous to the software programming. According to this model, hardware structures—brain regions—support the expression of the various aspects of God’s image, such as moral judgment. Brain chemicals are the means to mediate the communication between neurons and, ultimately, the different brain regions. However, brain structures and biochemistry are not the source of moral judgments. Instead they are part of the physical apparatus and operations that make the expression of moral judgments possible.

If the hardware of a computer doesn’t function properly, the software, though it may be fully intact, cannot work either. In like manner, the brain can be altered, influencing how the image of God is expressed. In this way, increasing or decreasing serotonin levels may impact one’s sensitivity to inflicting harm, but serotonin is not responsible for creating the ideal that causing harm is wrong.

This model also suggests a way that the Holy Spirit could operate to influence our behavior: through the serotonin levels in our brain. It is interesting that the researchers noted that “after citalopram, subjects were less likely to advocate harming an innocent bystander and more likely to ‘turn the other cheek’ and forgive unfair behavior.”4

  1. Molly J. Crockett et al., “Serotonin Selectively Influences Moral Judgment and Behavior through Effects on Harm Aversion,” Proceedings of the National Academy of Sciences, USA 107 (2010): 17433–38.
  2. Ibid., 17436.
  3. Fazale “Fuz” R. Rana, “Magnets and Morality,” New Reasons to Believe 2, no. 3 (2010): 14–15,
  4. Molly J. Crockett et al., 17436.