Fessler’s (2006) study of an evolutionary basis for disgust in pregnant women

1. Fessler’s (2006) study of an evolutionary basis for disgust in pregnant women Aim: To investigate whether the ‘morning sickness’ experienced by pregnant women has an evolutionary basis. Procedure: A sample of 496 healthy pregnant women aged between 18 and 50 years old was used. The women were asked to consider stomach churning scenarios such as: • Walking barefoot and stepping on an earthworm • Someone accidently sticking a fishhook through their finger • Maggots on a piece of meat in a outdoor trashcan Before asking the women to rank how disgusting they found the scenarios (using a survey), Fessler posed a series of questions, designed to determine whether they were experiencing morning sickness. For those in the first trimester, they found the scenarios involving food most disgusting.

2. Fessler’s (2006) study of an evolutionary basis for disgust in pregnant women Findings & Conclusions: In keeping with Fessler’s theory, women in the first trimester of their pregnancy scored much higher on scores across the board on disgust sensitivity than their counterparts in the second and third trimester. According to Fessler, many diseases that are most dangerous are food borne, but our ancestors could not afford to be picky about what they ate all the time. Natural selection may have helped compensate for the increased susceptibility to disease during this risky period in pregnancy, by increasing the urge to be picky about food. That sensitivity seems to diminish as the risk of disease and infection decreases – this is consistent with the view that disgust is a protection against disease. Evaluation: MECG?

3. Curtis et al. (2004) Internet survey on disgust responses Aim: Curtis et al. (2004) aimed to carry out research on the Internet to test whether there were patterns in people’s disgust responses. Procedure: They used an online survey in which participants were shown 20 images. For each image, they were asked to rank their level of disgust. Among the 20 images were seven pairs in which one was infectious or potentially harmful to the immune system, and the other was visually similar but non-infectious—for example, one pair was a plate of bodily fluids and a plate of blue viscous liquid. There were 77 000 participants from 165 countries.

4. Curtis et al. (2004) Internet survey on disgust responses Findings & Conclusions • The findings confirmed that the disgust reaction was most strongly elicited for those images which threaten one’s immune system. • Interestingly, the disgust reaction also decreased with age. • As the graph below shows, disgust reactions were higher in young people than in older people. • In addition, women had higher disgust reactions than men. • Once again, this supports the idea of disgust as a key to successful reproduction.

5. The original survey can be found at www.bbc.co.uk/sciencehurnanbody/mind/surveys/disgust

6. Evaluative points for evolutionary theory In spite of such evidence, there are some things to consider when examining an evolutionary argument. • The theories are speculative – its difficult to carry out experiments to clearly prove the theories • Since it may be difficult to test empirically some evolution-based theories, researchers may be susceptible to confirmation bias— that is, they see what they expect to see. The researcher Hayes (2005)states that there is a tendency to ignore findings that don’t fit in with the theory confirmation bias • Little is known about the behaviour of early Homo sapiens, sostatements about how humans used to be are hypothetical. • Evolutionary arguments often underestimate the role of culture/nurture/the present environmental influences in shaping behavior.