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Examine Two Evolutionary Explanations of Behaviour Essay

Charles Darwin’s theory of evolution puts forward a statement, ‘Survival of the fittest’. This is widely considered true, but in reality truth is a slight variation of this, more commonly known as natural selection. The survivors are the ones who adapt best to their environment and are then able to reproduce. This means that there genes carry on through the generations and we gradually see the preferred characteristics for survival become more common. Over time the human race will become more and more adapted for survival on earth and this process is called evolution.

Psychologists look at the behavioural aspects of people in order to work out whether the behaviour of humans has been determined through evolution. They have done this by studying our mechanism determining levels of disgust and the way we prefer one food or type of food over another food, e.g. taste.

Our way of determining what is ‘disgusting’ is really a way of stopping us from touching or coming into contact with things that would be harmful to us. This is because these things are supposed to impede our ability to survive. Therefore, humans have adapted so that we are disgusted by these objects.

In 2006 Fessler conducted a study on pregnant women who were in their first trimester of their pregnancy and studied their nausea in reaction to certain samples. Fessler hypothesised that these pregnant women would have a higher level of disgust because of their pregnancy. In the first trimester of pregnancy, the immune system of the mother is suppressed so that the foreign body (the baby) growing their womb is safer. Therefore, to keep the women safer, the body develops a heightened sense of disgust to protect itself.

Fessler conducted his research on 496 participants (Ps), pregnant women, who were aged 18-50, but were at different points in their pregnancies. This was in order to separate the results and compare the results of women in their first trimester to those of women in their second or third trimestres. All of these women had had normal pregnancies thus far and were considered healthy. He gave each of the women 32 scenarios and asked the women to rate the scenarios by level of disgust.

Fessler found that women in their first trimester of pregnancy had a higher sense of disgust than those in their second or third trimesters. This supported Fessler’s hypothesis. Therefore, he concluded that the heightened sense of disgust was advantageous, because it allowed our ancestors to survive for much longer and also allowed their genes, which helped them to surviv, to pass to their offspring. The results also show that there was a diminishing level of disease threat when women are pregnant, because there is not as much of a chance that women will become ill from food, because they will be disgusted by these foods. Therefore, the will be more picky about food. This proves the fact that their disgust mechanism has over-compensated, because the immune system is being suppressed.

This study uses a large sample of 496 women. Therefore, the study has population validity. As a result, we can apply the researcher’s findings to a large part of society. Furthermore, the study has cultural validity, because of its large sample. Therefore, it can be applied to people who are from vastly different backgrounds. Lastly, Fessler had a control group to compare results to. This was a group that contained women who were sick in their first trimester and women who were not. The fact that Fessler had a control group makes the results much more reliable. Consequently, we can say that these results are both reliable and valid.

On the other hand, the research has many problems with it. One of which is that there are too many scenarios to rate for disgust. Therefore, the Ps may have become de-sensitised by the end of the scenarios or may have felt more disgusted. Furthermore, these results may not reliable. To obtain more reliable results, Fessler should have only used 15-20 scenarios, this leaves him with enough data to complete his research, but is less likely to affect the P. The second problem is that there are demand characteristics. This means that Ps might change their results to help the researchers to find what they want, or might purposefully go differently in order to screw up the results. This means that we cannot rely on the results. Lastly, we do not know the rating scale he used. A scale from 1-an odd number would not be useful because Ps are able to sit on the fence. Therefore, the best scale would be one which ranges from 1-4.

In another experiment, 77000 Ps were studied by Curtis et al. (2004). They were studied to see whether there were patterns in people’s disgust responses. These Ps were from 165 different countries. Curtis made all of the participants take a 20 scenario survey like Fessler’s survey. There were seven pairs of photos that looked like its paired photo, but one was shown as an infectious substance.

Curtis et al found that the subtstances which would harm humans the most were the substances that were rated as the most disgusting by the Ps. The researchers also found that levels of disgust decreased with age and that women generally had much higher levels of disgust than men. This supports the concept that Fessler supported. That disgust is a way of protecting the unborn child when the immune system is being suppressed.

This study has population validity, because it has an extremely large sample (77000 Ps). Therefore, we can apply this to most sectors of society. It also has cultural vailidty, because the Ps are from 165 different countries. This means that we can apply the findings to people from all over the world. Lastly, the test is not too long for it is only 20 scenarios long. This means that the P is unlikely to become de-sensitised or become too disgusted. As a result the research is much more reliable.

However, this study doesn’t have ecological validity, because the Ps are looking at pictures on a screen instead of the actual object. This means that disgust may be influenced by other senses like smell and hearing. An improvement because of this may be to actually show the Ps the samples as an object in front of them.

Psychologists have also looked to explain other behaviours like what foods we like. For example, as humans, most of us like to eat sweeter foods like fruit.  In 1928 Davis investigated the eating behaviour of infants and young children in a paediatric unit. They did thi9s by monitoring the foods that the children chose.Davis found that have ‘an innate regulatory mechanism and are able to select a healthy diet. Furthermore, they tended to choose sweet or salty food while avoiding foods that are bitter. Davis concluded that the preference for sweet food could be because our ancestors needed to eat sweeter, high fructose and glucose foods like fruit, which contain the calories need for energy.

Also the preference for salty foods may have been our ancestors preference for meat in their diet. This was for a good source of protein, for growth. The natural avoidance of bitter foods would have helped ancestors protect themselves from eating poisonous foods. Nowadays our preference for sweet foods is satisfied by high-calorie products such as sweets and fizzy-drinks. This research has ecological validity, because the choices of the children were only monitored by the researchers and weren’t forced. This means that the results are valid for the children in this environment. However, this experiment has many problems. One of which is that it doesn’t have population validity. This means that the results cannot be generalised to most of the population. The research only includes one paediatric unit.

This means that the study doesn’t have cultural validity. As a result, we cannot generalise the findings of the study to lots of countries or areas of society. To achieve cultural validity, they should’ve used various paediatric units across the world. Another study looking into the food preferences of children was Desor’s study in 1973. Desor studied the facial expressions and sucking behaviour of new born babies. Desor ended up studying 83 different children from the ages of 4-7 (42 girls and 41 boys). The study was similar to Davis’ study, but the children were studied in a classified room after the children had acclimatised to their surroundings. They found that that the children preferred sweet-tasting substances which challenges what Davis’s study had stated (children has an innate regulatory mechanism making them choose a healthy diet).

This study doesn’t have population validity, because the sample is not big enough to generalise the findings of the research to the general population. They should have advertised across the country, resulting in much more data. It also doesn’t have cultural validity, because they only got Ps from the local area. This is known because they advertised for Ps in local newspapers. Therefore, the findings cannot be applied to people from other cultures. In conclusion, there is a way to explain food preferences as described in studies. For example, humans prefer sweet foods because of ancestors need for food with high levels of fructose or glucose like fruit (according to David 1928).


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