Paper 1 - Biological Approach - Genetics and Behavior - Evolutionary Explanations of Behavior

Evolution

the changing in the inherited traits of a species over time.

Charles Darwin's theory of natural selection

proposes that members of a species that are better adapted to the environment are more likely to survive, reproduce, and pass on these traits.

Survival of the fittest

the process by which species change to adapt to their environment.

Adaptive behaviors

behaviors which increase the chances of survival and reproductive success, which is why they are pass through generations.

Evolutionary fitness

success at surviving and reproducing.

evolution and behavior

If certain behaviors are inherited through genes, and evolution ensures these behaviors are passed on to offspring, then the behaviors observed today should have an evolutionary explanation.

Digust and evolution

for example, disgust may have evolved to protect people from poisoning themselves or eating harmful substances.

If people wrinkle up their faces at the sight of pustulent wounds or rotting food, then they are more likely to avoid deadly illness or food poisoning.

curtis et al (2004) aim

To test the hypothesis that disgust is an adaptation that serves to prevent disease.

Curtis method

· A survey instrument was placed on the BBC Science website and completed by over 77,000 people from 165 countries. Once improbable data had been removed, and those who had already seen a BBC programme that alerted them to the hypothesis were also removed, this left just under 40,000 respondents.

· Respondents were asked to rate 20 photographs, which appeared one‐by‐one on separate web pages, for disgust on a scale of 1-5. Randomly placed among the 20 photographs were seven pairs; one depicting a disease‐salient stimulus and another matched to be as similar as possible, but without disease relevance.

· A final question on the website asked respondents to choose with whom they would least like to share a toothbrush.

Curtis Results

· All seven of the disease‐salient images were rated as more disgusting by females than males who rated them.

· Feelings of disgust decreased with age, and in response to the final question regarding with whom participants would least like to share a toothbrush, the least acceptable was the postman (59.3%), followed by the boss at work (24.7%), the weatherman (8.9%), a sibling (3.3%), a best friend (1.9%) and the spouse/partner (1.8%).

Curtis conclusion

This gender bias in the result is consistent with women's enhanced evolutionary role in protecting the next generation. The decline with age is explained by the fact that older people have finished their reproductive life and are therefore evolutionarily disposable. The preference for toothbrush‐sharing with a partner rather than a stranger is explained thus: sharing a person's bodily fluids becomes more disgusting as that person becomes less familiar because strangers are more likely to carry new diseases and hence present a greater threat to another person's immune system.

Curtis evaluation

+ This was a large‐scale cross‐cultural survey with many participants and unlikely responses were excluded (all 1s in the answers or all 5s). The data was therefore robust and it seems that the significant differences found in six of the seven pairs between the levels of disgust when looking at the disease‐irrelevant picture and the levels of disgust shown at the disease‐relevant picture are reliable findings.

- 75% of the participants were between 16 and 65 years of age, with only 10% over 65 years old. Therefore, the age range shown on the graph is misleading, and the responses for under‐16s and over 65s come from a much smaller group of people.

Fessler et al (2005) aim

To investigate whether disgust sensitivity is adjusted as a function of the immune system, by testing the hypothesis that disgust sensitivity varies across pregnancy in a manner that compensates for changes in the vulnerability to disease.

Fessler method

Using a web-based survey of 496 pregnant women, with an average age of 28 years old, the researchers compared the disgust sensitivity of participants in their first trimester with those in later stages of pregnancy. 155 participants were in the first trimester, 183 in the second trimester and 158 in the third trimester. Responses from women who were in the second and third trimesters at the time of participation were pooled and compared with the responses from women who were in the first trimester.

The survey was a 31 item true/false and Likert style scale based on a questionnaire that required women to rate their disgust in eight areas including contact with animals, body products, death, hygiene etc.

Presence of morning sickness among participants was controlled for via the first question in the survey which asked women to rate their current level of nausea on a 16 point scale

Fessler results

Analysis revealed that participants in the first trimester reported greater overall disgust sensitivity than did participants in the second and third trimesters, and they also experienced more nausea. A simple correlational analysis revealed that overall disgust sensitivity was positively related to the current level of nausea throughout pregnancy.

Fessler conclusion

These results provide support for the hypothesis that disgust sensitivity varies during pregnancy in a manner that compensates for maternal and foetal vulnerability to disease

Fessler evaluation

+ Clear connections to evolutionary theory as the study illustrated an increased level of disgust among pregnant women versus the general population and specifically among women who were in their first trimester of pregnancy, a time at which the fetus is most vulnerable to infection. This establishes disgust as an adaptive behaviour.

- Hard to rank disgust; doing so is not consistent from participant to participant.

Evaluation of evolutionary explanations of behavior

- evolutionary theories are based on the assumption that behaviors are inherited. As we know from studies of genetics, it is difficult to know the extent to which certain behaviors are, in fact, genetically inherited.

+ these two studies triangulate each other.