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IB SL/HL Psychology (biological approaches to behaviour): Discuss one or more evolutionary explanations for one behaviour.
A level 7 essay discussing one or more evolutionary explanations for one behaviour.
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Examine one evolutionary explanation of behaviourEvolutionary psychology is grounded on the principle that over time, as genes mutate, those that are
advantageous are passed down through natural selection and the genes that benefit survival most are
passed on to the next generation. Charles Darwin proposed the theory of evolution and suggested that
those who adapt best to environmental challenges will have a greater chance of survival, reproduction and
passing on of genes. If a behaviour exists in humans today, then it must have helped in human survival and
reproduction in the past. The key assumption of all evolutionary research therefore is that human
behaviour must have been adaptive under some circumstances in the past. This essay will attempt to
uncover the assumptions and interrelationships of the evolutionary explanation of emotion and in
particular the behaviour of disgust.
In 2005, Fessler conducted an online survey of 496 pregnant women using a 31-itemed questionnaire to
investigate whether disgust sensitivity varied during pregnancy. Pregnant women aged between 18 and 50
were recruited by pregnancy related sites and were asked a series of questions to determine whether they
were experiencing morning sickness. Participants were then asked to consider 32 potentially stomach-
turning scenarios and rate how disgusting it was on a 16-point scale. The results from the study showed
that there was a heightened disgust sensitivity in the first trimester of the pregnancy, notably including
disgust sensitivity in the food domain. This pattern is not simply a consequence of elevated nausea during
the first trimester. Although disgust sensitivity and current level of nausea are correlated, first trimester
women remained more easily disgusted in the food domain even after controlling the greater incidence of
nausea. The researchers also found that women in the first trimester scored much higher across the board
in disgust sensitivity than women in their second or third. These results are due to the fact that many of
the diseases that are most dangerous to women in the first trimester of pregnancy are food-borne. Natural
selection may have helped compensate for the increased susceptibility to disease during the risky period of
pregnancy, by increasing the urge to take care regarding food. The sensitivity seemed to diminish as the
risk of disease or infection decreased in later pregnancy and this is consistent with the view of disgust as a
form of protection against disease.
Fessler’s study shows that women in the first trimester had a higher disgust sensitivity, especially with
food. This shows that sensitivity is increased when the risk of contracting a disease is increased, showing
the behaviour of disgust as a form of protection against disease. However, there is no cause and effect, due
to the fact that the findings only suggest a correlation between the sensitivity to disgust in the situations
and which trimester of pregnancy the women were experiencing. This therefore significantly reduces the
credibility of the study as no definite conclusions can be made since the researchers cannot be certain of
the relationship between two aforementioned factors. It is also very difficult to rank disgust as doing so is
not consistent from participant to participant, therefore results my not be as accurate as they potentially
could be, hence reducing the reliability and internal validity of the results found. Nonetheless, the use of
variables was a strength to this study as variables such as nausea through morning sickness were
controlled which successfully shows the disgust response as a function of pregnancy, not nausea. The
control of variables ruled out the effect of any extraneous variables, thus making the research more valid.
Furthermore, there are very clear connections to Charles Darwin’s theory of evolution and because his
theory is widely accepted, it is able to support the findings of Fessler’s researcher, making it even more
reliable.
Before Fessler’s research, in 2004, Curtis found that this disgust reaction described may actually be used to
prevent sicknesses as research suggests that disgust aids the survival of the human species and is therefore
an evolutionary behaviour. He first carried out research on the internet to test whether there were
patterns in people’s disgust responses. 77,000 participants were used from 165 countries, who completed
an online survey in which participants were shown 20 images. For each image, participants were asked to
their level of disgust from 1-5. Among the 20 images, there were seven pairs in which one was infectious or
potentially harmful to the immune system and the other was visually similar but not infectious. The
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