Paper 1 - Biological Approach - Hormones and Behavior - Pheromones

Pheromones

Chemicals that an animal produces, which changes the behavior of another animal of the same species. They are secreted by glands to act outside the body, serving as a communication between individuals of the same species. This communication can include sexual attraction and mammal olfactory simulation between lactating mammals and infants. Studies into butterflies and mammals (e.g. mice and monkey) have provided evidence for the signalling role of pheromones.

Two possible human pheromones

Two possible human hormones are Androstadiene (AND) and Estratetraenol (EST).

AND is an odorous steroid found in greater amount in men and is supposed to signal male gender.

EST is an odorous steroid found in greater amount in women and is supposed to signal female gender.

Issue with pheromones

No pheromone has been identified as a human pheromone. This may be because humans lack the organ mammals use to detect hormones - the vomeronasal sensory organ (VNO), a collection of neurons deep in the nose that transmits signals via the accessory olfactory bulb to the hypothalamus in the brain.

Evidence for the existence of human pheromones

Some evidence for the existence of human pheromones includes the fact that other mammals have them. We also secrete scents like other mammals. McClintock (1998) found evidence of the synchronisation of the menstrual cycles of female college students over a time period.

Zhou et al: aim

To investigate the chemosensory communication of gender in a sex-specific manner, through testing male and female reactions to the human pheromones AND and EST.

Zhou method

They used a sample of 96 self-reported homosexual or heterosexual males and females (24 in each group). The homosexual female group included self-reported bisexuals. The AND, EST and control substance were presented in identical small jars, from which participants inhaled during the experiment. There were 15 light dots positioned at the major joints of walkers (taken from 50 male and 50 female walkers on treadmills). The participants were asked to rate the walker's gender under each condition: AND inhaled, EST inhaled, and control substance inhaled.

Zhou results

Zhou et al. found that smelling AND biased heterosexual females and homosexual males towards perceiving the walkers are more masculine and smelling EST biased heterosexual males towards perceiving the walkers as more feminine. The results from bisexual and homosexual females fell in between those of heterosexual females and males.

Zhou conclusion

They concluded that the 2 human steroids communicate opposite gender information that has a differential effect on the two sex groups, based on their sexual orientation. This shows that human perception and behaviour is the result of subconscious chemosensory biological cues, therefore supporting the theory that human pheromones exist.

Zhou evaluation

+ It was a well-controlled lab experiment. Participants were unaware of the nature of the olfactory stimuli as they were all in identical small jars. This means they could not exhibit any demand characteristics (e.g. the 'please you' effect and 'screw you' effect). This therefore increases the validity of the study.

- It may not reflect real life. The amount of AND and EST were far above what would be found in the human body naturally. Therefore, the study may lack ecological validity, as we cannot know if the smaller amounts that exist naturally would produce the same effect.

Evidence against the existence of human pheromones

The generalisations made from animal research have not been proven to be valid yet and studies on human pheromones have often not been replicated. Furthermore, human mating behaviour is influenced by cognitive and sociocultural factors, including learned experience and social norms. Additionally, the human process of scent detection is very complex and different to study. The human scent is complex and made up of many different molecules - which no one has not yet mapped. Contrasting with McClintock's findings, Trevathan et al. (1993) found no evidence of synchronicity in the menstrual cycle of 29 lesbian partners, contrasting with McClintock's findings.

Hare et al: aim

To investigate if AND and EST have an effect on human judgement of gender, attractiveness, or unfaithfulness.

Hare method

The sample used was heterosexual and Caucasian. The study used a double-blind design throughout. The first task used a repeated measures counterbalanced design in which 24 males and 22 females completed 2 computer-based tasks twice, on 2 consecutive days, exposed to a control scent on one day and EST or AND on the other. They had to indicate the gender of 5 gender neutral facial morphs. The second task used the same design, in which 43 males and 51 females rated photos of opposite-sex faces for attractiveness and probable sexual unfaithfulness, under control and random allocation to AND or EST conditions.

Hare results

They found that exposure to AND and EST had no effect on gender perception, attractiveness ratings and unfaithfulness ratings.

Hare conclusion

They concluded that the hypothesis that exposure to AND and EST would alter perception of gender-neutral stimuli, and the attractiveness and probable unfaithfulness of potential mates was not supported. Therefore, AND and EST are unlikely to be human pheromones, contradicting the theory that human pheromones exist.

Hare evaluation

The study was highly controlled. This was a double-blind quasi-experiment, which prevents researcher bias. Furthermore, the researchers used counterbalancing to reduce any order effects like fatigue or practice. This level of control increases the validity of the study.

However, this experiment, like Zhou's, used concentrations of AND and EST that far exceed the naturally existing levels in the human body. Therefore, it is difficult to be sure the same results would be found in real life, and the results may therefore lack ecological validity.

Evaluation of pheromones

One strength of the theory that human pheromones exist is that there has been biological evidence to support it. unconscious observable brain responses to chemicals have been shown to exist: social behaviour, gender assignation and menstrual cycles seem to be affected by certain airborne chemical signals. However, the idea that these operate in exactly the same way as in animals or that in any one chemical has been identified as a pheromone has not yet been demonstrated.

A further weakness is that Wedekind et al (1995) demonstrated the MHC (major histocompatibility complex) influences both body odours and body odour preferences in humans, and that the women's preferences depend on their hormonal status. So, male and female attraction can act through perceptible odour and on an individual, not species, bias.