Behind every wave of disgust that comes your way may be a biologicalimperative much greater than the urge to lose your lunch, according to agrowing body of research by a UCLA anthropologist.
"The reason we experiencedisgust today is that the response protected our ancestors," said Dan Fessler,associate professor of anthropology and director of UCLA's Center for Behavior,Evolution, and Culture. "The emotion allowed our ancestors to survive longenough to produce offspring, who in turn passed the same sensitivities on tous."
Across a series of subtle and ingenious studies, Fessler has managed toilluminate the ways in which disgust may have served to protect our ancestorsduring such biologically precarious situations as pregnancy and to maximize thelikelihood of our forbears' reproduction when they were at their most fertile.
Fessler's research alsoillustrates how the emotional response that helped our ancestors may not serveus as well today and may actually promote xenophobia, sexual prejudices and arange of other irrational reactions.
"We often respond totoday's world with yesterday's adaptations," Fessler said. "That's why, forinstance, we're more afraid of snakes than cars, even though we're much morelikely to die today as a result of an encounter with a car than a reptile."
Fessler will present his findings at 2 p.m. on Friday, March30, as part of a three-day conference at UCLA on new research concerningemotions. The event, "Seven Dimensions of Emotion: Integrating Biological,Clinical and Cultural Perspectives on Fear, Disgust, Love, Grief, Anger,Empathy and Hope," which runs Friday through Sunday, March 30–April 1, willinclude 40 scholars from around the world. The conference will be held in KornHall at the UCLA Anderson School of Management and is sponsored by UCLA and theFoundation for Psychocultural Research.
Fessler's research helps shed light on why some body partsuniversally draw more "ewwwws" than others.In one study, Fessler asked 400 participants to imagine 20 differenttransplant operations and to rate them according to the level of disgust theyelicited.
Half of the transplant organs were appendages — like tonguesand genitalia — that routinely come into direct contact with the outside worldand are therefore more susceptible to infection and damage. The other half werelocated inside the body — like the spleen and heart — and much less under anindividual's control, especially with regard to protecting from infection anddamage.
"If disgust protected ourancestors from pathogens, the emotion would have had the most utility inprotecting parts of the body that interact most with the environment such asappendages," Fessler said. "Our ancestors would not have enjoyed the sameadvantage from disgust reactions with regard to protecting internal organs. Sothey benefited from focusing disgust reactions on the parts of the body thatare on the outside and interface with the world around us."
True to Fessler's theory,participants considered the idea of transplanting appendages more disgustingthan the idea of transplanting internal organs. Tongues, genitalia and anusesranked the most disgusting, while hips, kidneys and arteries turned the feweststomachs.
"The disgust we feel when we consider individual body partsreflects an adaptive goal of avoiding the transfer of pathogens," Fessler said.
The same logic appears to be behind some of the queasinessexperienced by women during the first trimester of pregnancy, when an infusionof hormones lowers the immune system to keep it from fighting the "foreign"genetic material taking shape in the womb. Because the consequences ofinfection are also greatest for the fetus during this period, Fessler reasonedthat natural selection may have armed pregnant women with an emotional responsethat helped compensate for their suppressed immune system.
To test the theory, Fessler gathered 496 healthy pregnantwomen between the ages of 18 and 50 and had them consider 32 potentiallystomach-turning scenarios, including "a 30-year-old man who seeks sexualrelationships with 80-year-old women," "walking barefoot on concrete andstep(ping) on an earthworm," "someone accidentally stick(ing) a fish hookthrough his finger" and "maggots on a piece of meat in an outdoor garbagepail."
But before asking the expecting women to rank how disgustingthey found these scenarios, he asked a series of questions designed todetermine whether they were experiencing morning sickness.
In keeping with Fessler's theory, women in their firsttrimester scored much higher across the board in disgust sensitivity than theircounterparts in the second and third trimesters. But when Fessler controlledthe study for morning sickness, the response only held for disgusting scenariosinvolving food, such as the maggot example.
"A lot of the diseases that are most dangerous arefood-borne, but our ancestors could not afford to be picky all the time aboutwhat they ate," Fessler said. "Natural selection may have helped compensate forthe greater susceptibility to disease during this risky point in pregnancy byincreasing the urge to be picky about food, however much additional foragingthat required. That the sensitivity seems to lift as the risk of disease andinfection diminish is consistent with the view of disgust as protection againstpathogens."
Fessler's research also suggests that at least somexenophobia may have its roots in the same vulnerable trimester. Together withcolleagues, he asked 206 healthy American pregnant women between the ages of 18and 42 to read two essays — one obviously written by a foreigner critical ofthe
"Since the need for assistance from any other human beingincreases with pregnancy, the response doesn't make sense unless you consideroutsiders as carriers of disease and infection," he said. "We suspect that,around the world, cultures have discovered that an easy way to elicit prejudicetoward outsiders is to associate them with illness. Because emotional reactionsthat protect against disease are elevated during the first trimester,xenophobia comes along for the ride and is similarly increased early inpregnancy."
Women also appear to feel increased disgust toward certainforms of sexual behavior during the time in their menstrual cycle when they aremost likely to become pregnant. Fessler administered the same standardizeddisgust scale that he used with pregnant women to 307 women between the ages of18 and 45. In addition to the scenario about sex between couples separated bygreat spans of age, the disgust scale included scenarios involving incest andbestiality. Around the time ofovulation, women consistently rated these sexual activities as more disgustingthan did women at other points in their menstrual cycle.
"Since women have been shown to be the most interested insex and new experiences when they are the most fertile, their disgust reactionstoward unusual forms of sexual behavior during ovulation don't make senseexcept when considered in the context of reproductive fitness," Fessler said. "These are sexual activitiesthat either would not result in conception or — in the case of incest and sexwith older people — were less likely to result in conception of healthychildren, so women who were more disgusted by them during ovulation would bemore likely to reproduce and to have healthy children."
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