Applying the assessment rubric

Below you will see three samples SAQs for the following SAQ from the biological approach:

Explain one study of one evolutionary explanation of one behaviour.

Which one do you think is the best?  What advice would you give the other two students?

Script 1.

One of the things that can influence our choice of partner is their MHC - Major Histocompatibility Complex, a group of genes that seem to play an important role in the immune system, and is expressed through body odour. Since the genes for immunity are expressed co-dominantly, it is in the partner's interest to have different versions of the gene to give better immunity to their off-spring.

Wedekind decided to carry out a study and assess if the MHC had an effect on the mating choice of university females. He first tested each participant for their MHC type and noted if the females were taking oral contraceptives. He then asked the males to sleep in the same shirt for two days and not to use any deodorant so that they would not change their natural body odor on the shirt. He then asked the female students to come to the lab and smell and score 7 different boxes with shirts inside them - three were from males of a different MHC than the female, three were from males of the same MHC as the female, and one was a clean shirt that was used as the control. The females scored the pleasantness of the smell of each shirt. The results showed that the females preferred the odor of the shirt from a male with a different MHC than they themselves had, but oral contraceptives caused this result to be reversed, implying that the contraceptives change a female's sense of smell and therefore influence her partner choice for the worse. (259 words)

Script 2

Evolutionary arguments have been used to explain human mating behaviour. Evolutionary psychologists argue that our behaviours are the result of natural selection – that means that the behaviours that most improve our chances of handing down our genes and producing healthy offspring, these behaviours will continue.

Wedekind (1995) carried out a study to see to what extent MHC alleles play a role in mating behaviour. MHC alleles are responsible for our immune systems. They are inherited from both of our parents – and they are codominant. That means we end up with both immune systems. He argued that our “smell” is based on our MHC and it is best for a woman to choose a mating partner who has a different smell in order to maximize the immune system of her child.

Students were used in the study. The men were asked to wear a t-shirt for two nights. They were also told not to wear any perfume and to avoid spicy food, smoking and alcohol. They were also told not have sex. The researchers wanted to make sure that the men would not change their natural smell.

Two days later the women were asked to rank the smell of the t-shirts. They were tested in the second week after the beginning of menstruation when they have a better sense of smell. T-shirts were placed into boxes with a “smelling hole.” 3 boxes contained t-shirts from men with the same MHC as the woman, three were different and one was a clean t-shirt. Every woman rated the shirts for their “pleasantness.”

The women scored the t-shirts as more pleasant when the MHC was different than their own. This suggests that MHC influences human mate selection. If the woman’s mate has a different MHC allele, then both that allele and her allele will be inherited and expressed by a child, thus increasing its immune system and chances of survival. Research also shows that when a woman's partner has the same MHC as she does, she has a higher risk of miscarriage.  It makes sense that it would be to a evolutionary advantage to choose a partner with a different MHC in order to increase the health of our children and increase their potential for reproduction.  (372 words)

Script 3

Evolutionary psychologists argue that our behaviour is inherited. One study that looks at this argument is a study by Caspi who argues that depression may be inherited by a mutation of the 5HTT gene which is responsible for serotonin transport.  Caspi did a study in which he took a sample of both healthy people and people diagnosed with depression.  He then did a blood test to find out who had the two short 5HTT alleles.  He found that the participants with the two short alleles were the ones that had depression.  In addition, he found that those with the two short alleles who also had at least three stressful events in their lives in the past year were more likely to have depression.  This of course, raises some questions of whether it was actually the stressor, or the gene itself which led to the onset of depression.  Since the gene is inherited, it clearly shows a link to evolution and how the variation may have an advantage to human survival. (170 words)