Examine one evolutionary explanation of behaviour.

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. For example, the emotion of disgust.

 Fessler (2006)

• Investigated women's experiences of nausea in first trimester of pregnancy (resulting in morning sickness).
• During the first trimester, hormones suppress the immune system in order to accustom the body to the foreign genetic material growing in the womb.
• He hypothesised that the heightened sense of disgust experienced by women during this time was the body's way of compensating for the lacking immune system.
• Participants: 496 healthy pregnant women, ages 18-50.
• Asked them to consider 32 disgusting scenarios, and rank disgustingness.
• Women in their first trimester consistently ranked higher than their counterparts in second and third trimesters in terms of disgust-sensitiveness.
• As many of the most harmful diseases are food-borne, Fessler concluded that a heightened sense of disgust was advantageous to our ancestors and allowed them to survive long enough to produce offspring, who passed on the same sensitivities.
• It would have helped compensate for the increase susceptibility to disease during early pregnancy, which is a risky period due to the suppressed immune system, by increasing the urge to be picky abut food.
• This would diminish the risk of food-borne disease during pregnancy, which is according to the view of disgust as a form of protection against disease.

Curtis et al. (2004)

• Investigated whether there were patterns in people's disgust responses.
• Participants: 77 000 altogether, from 165 different countries.
• Conducted an Internet based survey in which participants were shown series of 20 photographs, an asked to rank each image for how disgusting it was.
• There were seven pairs in which one was infectious and a matching image was not (e.g. body fluids, coloured liquid).
• Those images containing substances that would most strongly harm the immune system were rated highest on disgustingness.
• Disgust decreased with age and female were more disgusted than males, which supports the idea that disgust is a form of protection to enhance chances of successful reproduction.

There are some points to consider when using evolution-based explanations for behaviour:

1. It is difficult to test evolution-based theories empirically, so researchers may be susceptible to confirmation bias (finding results that they expect).
2. Very little is known about the behaviour of early Homo sapiens, so hypotheses about this are just that - purely hypothetical.
3. Evolutionary arguments can easily underestimate the role of culture and cultural evolution as a factor in the development of human behaviour.