The Human Brain

The Human Brain

Wednesday, December 17, 2008

Yuck! More Evidence that Disgust Influences Our Moral Judgments

Disgust is an emotion that has evolved to protect us from ingesting toxins that could be potentially harmful to our survival and ultimately, to our ability to pass on our genes. Charles Darwin (1872) described disgust as “something revolting, primarily in relation to the sense of taste as actually perceived or vividly imagined” (p. 253). As demonstrated by Paul Ekman’s research, disgust is a cross-cultural human emotion. Humans in all cultures recognize the distinctive facial expression of the wrinkled nose, curled lips and protruding tongue as a reaction to disgusting stimuli.

Although the emotion of disgust has evolved to protect us from the consumption of harmful toxins, it is also intimately involved in our moral decision-making. Haidt (2000) proposed an intuitional model of moral judgments. His model suggests that our moral decisions are based on automatic, emotional reactions rather than conscious reasoning. According to his model, moral reasoning provides us with a post hoc rationalization for our moral judgments rather than the moral judgment itself.

The automatic emotions that influence our moral judgments are referred to as moral emotions. They include emotions such as anger, disgust, embarrassment, empathy etc. Rozin and Haidt (2000) extended the definition of disgust to include disgust moral offenses. In support of their new definition of disgust, Rozin and colleagues (1997) found that moral vegetarians are more disgusted by meat than health vegetarians. Recent research has also suggested that sensitivity to disgust is related to ethnocentrism (Navarrete & Fessler, 2006) as well as various politically conservative issues including abortion, immigration, homosexual marriage and stem-cell research, as well as prejudice toward homosexuals (Terrizzi & Ventis, 2006; Inbar, Pizarro, Knobe & Bloom, 2008). Disgust sensitivity has also been found to be correlated with other variables such as right-wing authoritarianism, religious fundamentalism (Terrizzi & Ventis, 2006) and religious obsessions (Olatunji, Tolin, Huppert & Lohr, 2005).

More recently Schnall and Colleagues (2008) conducted a series of four experiments in which they manipulated disgust using “fart spray”, making the lab dirty (stained and stick desk, chewed pen, pizza boxes, etc.), recalling disgusting experiences and showing disgusting video footage. The results of their first study indicated that the participants who were exposed to the “fart spray” had more severe moral reactions to first cousins marrying and having sex. In the remaining studies, the researchers found that disgust only influenced the moral judgments of those who exhibited high levels of private body consciousness.

Our moral judgments may not be as rational as we like to think that they are. Research is beginning to reveal that our behavior and decision-making is often determined by automatic, emotive processes, which have evolved to ease our decision-making in order to make it easier for us to function adaptively in our social worlds. The evidence here suggests that disgust is one of those emotions that can influence our moral decision-making. Disgust, which is an emotion that has evolved to protect us from consuming potentially harmful substances, can be co-opted by our moral decision-making processes to make decisions about moral issues.

Darwin, C. (1872). The expression of emotion in man and animals. Chicago: University of Chicago Press.

Haidt, J. (2001). The emotional dog and its rational tail: A social intuitionist approach to moral judgment. Psychological Review, 108(4), 814-834.

Inbar, Y., Pizarro, D., Knobe, J., & Bloom, P. (2008). Disgust sensitivity predicts intuitive disapproval of gays. Manuscript submitted for publication.

Navarrete, C. D., & Fessler, D. M. T. (2006). Disease avoidance and ethnocentrism: The effects of disease vulnerability and disgust sensitivity on intergroup attitudes. Evolution and Human Behavior, 27(4), 270-282.

Olatunji, B. O., Tolin, D. F.; Huppert, J. D. & Lohr, J. M. (2005). The relation between fearfulness, disgust sensitivity and religious obsessions in a non-clinical sample. Personality and Individual Differences, 38(4), 891-902.

Rozin, P., Haidt, J., McCauley, C., & Imada, S. (1997). Disgust: Preadaptation and the cultural evolution of a food-based emotion. In H. MacBeth (Ed.) Food preferences and taste. Providence: Berghahn Books, 65-82.

Rozin, P., Haidt, J., & McCauley, C. R. (2000). Disgust. In M. Lewis & J. M. Haviland-Jones (Eds.), Handbook of emotions, 2nd Edition (pp. 637-653) New York: Guilford Press.

Schnall, S., Haidt, J., Clore, G., & Jordan, A. (2008). Disgust as embodied moral judgment. Personality and Social Psychology Bulletin, 34(8), 1096-1109.

Terrizzi, J., & Ventis, L. (2007, May). Prejudicial attitudes toward homosexuals: The competing roles of moral reasoning and the moral emotion of disgust. Presented as a talk at the annual meeting for the Human Behavior and Evolution Society, Williamsburg, VA.

Sunday, February 10, 2008

Top Five Reasons for Wanting a Presidential Debate on Science

The first editorial in the February 7th issue of Nature discusses a petition for a presidential debate that would focus on scientific and technological issues. There has been significant support for the idea of a presidential debate on science.

Numerous Nobel laureates, scientific organizations, government leaders, and renowned scientists have signed the petition. Some of the organizations and individuals who have joined the campaign include Science Magazine, American Association for the Advancement of Science, Skeptical Inquirer Magazine, Craig Venter, Steven Pinker, Sean Carroll, James Watson, and my personal favorite, Bill Nye the Science Guy. For a complete list go to

Here are my top five reasons for wanting a presidential debate that focuses on science.

1. I want a well informed president who understands the value of having a premier scientific community. I want a president who does not allow faith to stand in the way of scientific advancement, who understands the value of reason and skeptical inquiry. I want a president who understands the value of changing positions when the evidence supports it.

2. Whether we believe it or not, our planet is getting warmer and most scientists agree that we are at least partially to blame. I want a president that will address the problem of global warming and climate change and will listen to the recommendations of the scientific community.

3. I want a president who will support stem cell research even if the ethical issues are still not resolved.

4. I want a president who will make funds available for the development of alternative fuel sources.

5. I want a president who will not allow creationism in the class room, a president who understands the value of teaching evolution.

Please consider signing the petition for a presidential debate on science. We do not want another president who will neglect science.

Sunday, February 3, 2008

Why We Kill Each Other: The Evolution of War

In order to understand why we kill each other, the concept of war must be approached from an objective perspective. It is too simplistic and uninformative to qualitatively state that all war is bad or that all war is good. The role of the scientist is not to inform us whether a war (or war in general) is morally right or wrong. It is, however, the scientist’s role to help explain why we kill each other. What function does it serve? What triggers it? Scientists and specifically anthropologists, biologists, and psychologists, who study human beings, have a great responsibility when it comes to explaining war.

Last year, Steven Pinker gave a lecture on violence. He explained that years of data suggest that the prevalence of violence is lessening. Even though that may be the case, he indicates that this finding should encourage us to be complacent. War is still a problem that could threaten the survival of our species. Pinker suggests that we approach the question of war differently. We should not be asking why we go to war. We should be asking why we are becoming more peaceful. The answer to this question may provide us with a solution to the problem of war.

My perspective is that we need to be asking both questions. We need to know why we fight. What function does it serve? On the other hand, we also need to be asking the question: “What makes us peaceful?”

In David Livingstone Smith’s book, The Most Dangerous Animal, Smith approaches the problem of war from both angles. Early theories of human nature have insinuated either that human beings were innately good or inherently evil. Like the nature vs. nurture theory that we were taught in college, this is a false dichotomy. Humans are neither good nor evil. There are times when we do dastardly things and there are times when we are altruistic. The idea of the noble savage is a myth as is the idea that primitive humans were barbarous murders (although you are far more likely to be murdered in a hunter-gatherer society than you are in an agrarian culture).

David Livingstone Smith provides vivid anthropological evidence of war in our ancestral past. He also elucidates a similar phenomenon, raiding, in our closest living relatives, the chimpanzee.

One of the reasons that people do not like to approach topics such as war from an evolutionary perspective is because they falsely assume that it moralizes issue. They believe that providing an evolutionary explanation for war somehow justifies it. This is simply not true. It is known as the naturalistic fallacy, the belief that whatever occurs in nature is good.

Additionally, people dislike the evolutionary approach to war because they think that it relieves people of responsibility. If there is a biological explanation for something, it is impossible to hold someone responsible for it. Fear of biological determinism is not a sufficient excuse for understanding the evolutionary biomechanics of war.

These people who are worried about evolutionary explanations of human behavior are also afraid that such explanations may brand behaviors as incurable. This is also simply untrue. For example, consider nearsightedness or myopia. Myopia is a biological problem, which can be cured by corrective lenses or lasik eye surgery. The only way that we can correct the problem of war is if we can understand truth about why we fight.

So why do we fight? David Livingstone Smith did an excellent job of providing evidence for our evolutionary and biological penchant for war and provided some insight into why we fight. However, you still come away from the book unsatisfied with our current understanding of war. Smith’s greatest success was getting the dialogue of an evolutionary understanding of war started. To my knowledge, his is the first book written on the topic.

There is no satisfying answer to the question of why we go to war. But there are several interesting insights. Humans are equipped with a sense of kinship. We love the people who share our genes, whether we like it or not. Our sense of kinship does not stop at genetic relatedness. We also have a sense of kinship with the groups that we affiliate with and we will do anything to protect them. Our kinship is often exploited by nations and religions, not surprisingly the two institutions that are responsible for most, if not all, wars. The short and unsatisfying answer of why we fight is because it feels good. We become enthused zealots who want to destroy the evil that threatens our groups.

What stops us from killing? Fortunately, we have evolved a mechanism that also prevents us from killing. This is something we can be optimistic about. Most humans are endowed with a sense of disgust. When we see pictures of mutilated human bodies, we are appalled. Our sense of disgust with the murder of our fellow humans is so strong that most people who have killed other human beings are haunted by the memory and suffer from post-traumatic stress disorder.

David Livingstone Smith provides an excellent survey of war from an evolutionary perspective. His book is full of all sorts of insights that help explain why we fight and why we don’t. I recommend The Most Dangerous Animal to anybody who is seriously interested in understanding the mechanics of why we go to war.