A principle of evolutionary psychology is that as genes mutate, those that are advantageous are passed down through a process of natural selection. This is derived from Charles Darwin's theory of evolution, which states that all living things are related and descended from a common ancestor. Darwin explained this through his theory of natural selection, which is a mechanism through which all life came to be related - members of a species who have characteristics that are better suited for their environment, or are favourable for their environment, are more likely to survive to a reproductive age and pass on those characteristics to their offspring. Hence, offspring have those characteristics, which are passed down, etc. These characteristics can be physical traits or behaviours, which advantage the individual.
Evolutionary psychologists attempt to explain how certain human behaviours show how humans have developed over time. Certain behaviours can be explained by examining their evolutionary origins and their identifying their ability to enhance survival.
Matsuzawa (2007) – The aim was to compare the differences in spatial memory between chimpanzees and humans. The researchers trained three pairs of chimps to recognise numbers from 1-9. Both chimps and humans were seated in front of touch-screen computer where those numbers flashed in a sequence and then the participants had to remember in which location and sequence those numbers appeared. As the interval before numbers being replaced by white squares was shortened, humans made more errors, while chimps showed remarkable skills. This is believed due to their species’ environment that they need to survive in the jungle. Humans’ spatial memory skills were replaced by language memory skills. Darwin’s theory of natural selection says that any trait useful for survival in the environment will be kept. Humans and primates are believed to have a similar ancestor, so animal researches help us understand human behaviour and adaptation to environment.
Evaluation: A representative sample of humans was used, as there were adults as well as children, however, chimps were trained prior to the experiment, and so they do not pose a representative sample. The experiment was done in a laboratory, so that is an artificial setting. Ethical guidelines were followed.
Curtis et al. (2004) - Tested whether there were patterns in disgust responses via an online survey with 77 000 participants from 165 countries. They were asked to rank their level of disgust for 20 images, among which were some that were harmful to the immune system, accompanied with a similar picture, just not harmful. For example, one image was a plate of bodily fluid and its pair was a plate of blue viscous liquid. The disgust reaction was strongest for images, which threatened the immune system. Disgust also decreased with age and women had higher disgust reactions than men. This supports the idea of disgust as key to successful reproduction. As women are the carriers for offspring, they have a stronger disgust reaction so as not to threaten the lives of unborn offspring and consequently, the species.
Evaluation: It is difficult to know what early Homo sapiens used to be, so the theory of evolution is hypothetical. It lacks ecological validity, as well as is a bit unreliable because there was no real control over the participants. Low control over variables, no cause-and-effect.
Fessler (2006) - He argues that the emotion of disgust allowed our ancestors to survive long enough to produce offspring, who in turn passed the same sensitivities to us. In the first trimester of pregnancy, hormones lower women’s immune systems so that it does not fight the new foreign genetic material in the womb. Fessler hypothesised that disgust helps to compensate for the suppressed immune system. He asked 496 healthy pregnant women between ages 18 – 50 to rank 32 potentially disgusting scenarios. Before asking the women to rank the level of disgust in the scenarios, Fessler asked questions to determine whether they were experiencing morning sickness. Women in their first trimester scored higher in disgust sensitivity than women in the second and third trimesters. When Fessler controlled the study for morning sickness, the response only applied to scenarios involving food. Fessler explained this in terms of the large extent of dangerous diseases, which are food-borne. Being pickier with food would also help humans avoid diseases that could harm unborn offspring, and thus, threaten the species.
Evaluation: Study supports that disgust may be an evolutionary behaviour as it may assist reproduction of offspring and protection against disease, thus having a greater chance of surviving. Large sample – possibility to generalise. Data was obtained by self-report, which is often unreliable. Findings cannot be solely based on evolution, as the environment could be an interfering variable.