A revolting development
By Judy Lin
Published Jul 1, 2007 8:00 AM
Imagine a thick, juicy steak...swarming with maggots. Disgusted? Congratulations, you're evolved!
Disgust is a survival skill, says Dan Fessler, associate professor of anthropology and director of UCLA's Center for Behavior, Evolution, and Culture: "We experience disgust today [because] the response protected our ancestors, [allowing them] to survive long enough to produce offspring."
In one study, Fessler and colleagues asked 496 healthy pregnant women to consider scenarios that included the maggots-on-meat, fish hooks through fingers, and contact with feces or urine.
During the first trimester of pregnancy, increased levels of the hormone progesterone lowers a woman's immune system to keep it from fighting the "foreign" genetic material taking shape in the womb, making both the woman and her fetus extremely vulnerable. First-trimester women scored much higher in disgust sensitivity than counterparts in subsequent trimesters when it came to scenarios involving food — perhaps, Fessler reasons, a disgust response to protect against food-borne illness.
Fessler also believes that disgust has evolved to monitor sexual behavior as a means of ensuring healthy pregnancies, as evidenced by a study in which he found that women feel increased disgust toward certain forms of sexual behavior during the "luteal phase" of their menstrual cycle, when they're most likely to become pregnant. Fessler asked 307 women to consider potentially disgusting scenarios that included "a 30-year-old man who seeks sexual relationships with 80-year-old women," as well as incest and bestiality. Fessler found that around the time of ovulation, women consistently rated these "suboptimal" activities, which would not likely lead to conception of healthy kids, as more disgusting.
In another study, Fessler and his colleagues asked 400 people to imagine 20 different transplant operations and to rate them according to the level of disgust they elicited. Half of the organs were appendages like tongues and genitalia that come into direct contact with the outside world and are more susceptible to infection and damage. The others, such as the spleen and heart, were inside the body. Sure enough, participants found transplanting appendages more disgusting than transplanting internal organs.
The results of that study reflect "an adaptive goal of avoiding the transfer of pathogens," Fessler concludes. "Folks do not want a transplanted anus, but they're happy to have somebody else's spleen."