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What are pheromones?
chemical substances secreted by an individual into the environment, which influence the behaviour or physiology of the members of the same species.
They act as carriers of information between individuals, particularly in mating, social interaction, and survival behaviours.
They carry stimulation.
What are typed of pheromones?
Primer pheromones →
They cause long-term physiological and hormonal changes.
E.g., they could influence reproduction and development.
They work overtime, affecting hormonal systems.
Signalling pheromones →
They trigger immediate behavioural responses.
E.g., they influence mating behaviour or danger response.
They cause instant reactions in animals, such as mating readiness or fear response.
What is the difference between the pheromones in humans and in animals?
In animals, pheromones are well-documented for their role in mating and social organisation.
In humans, pheromone influence is highly debated.
humans do not rely exclusively on pheromones for communication.
Cognitive and social factors play a major role in human behaviour.
What is the biological mechanism of pheromone detection?
The Olfactory System
Pheromones are detected through the sense of smell.
In human, the presence of a functional VNO (Vomeronasal Organ) is debated:
The VNO exists in human fetuses but regresses after birth.
Even if present it is not connected to the central nervous system, meaning it likely does not function like in animals.
What are some potential human pheromones?
Androstadienone (AND)
Estratetraenol (EST)
What is androstadienone?
a steroid compound found in male sweat and semen.
Thought to influence mood, attraction, and female hormone levels.
What effects does andostadienone have on human behaviour?
May increase attraction towards males in heterosexual women.
Can elevate mood and increase focus in women.
Has little to no effect in heterosexual men.
What is the pheromone estratetraenol?
A steroid compound found in female urine.
Believed to influence mood and attraction in men.
What effect does estratetraenol have in human behaviour?
May increase attraction towards females in heterosexual men.
Can enhance social perception related to gender.
What are some arguments for human pheromones?
Other mammals have pheromones → suggests human have as well.
Some evidence exists (Wedekind)
AND and EST studies suggest smell influences attraction.
What are some arguments against human pheromones?
Lack of replication → many findings are inconsistent.
Publication bias → some studies are funded by commercial interests.
No identified functional human pheromone → no single chemical has been proven to affect human behaviour consistently.
Smell ≠ Pheromone → many scents come from bacteria, diet, and hygiene, not secreted pheromones.
Human behaviour is complex → mating and attraction are influenced by culture, cognition, and social norms, not just biology.
What studies support the theory of pheromones?
Wedekind
Zhou et al
When was Wedekind conducted?
1995
What is its aim?
Whether one’s MHC (Major Histocompatability Complex) is related to sexual attraction or would impact it.
What are the participants?
Students of a university:
49 female
The women had to use a nose spray for 14 before the experiment → support the regeneration of the nasal mucous membrane.
44 male
They were given perfume-free detergent to wash clothes and bedclothes and perfume-free soap for showering.
They were asked to not use any deodorants or perfumes, to refrain from smoking tobacco or drinking alcohol, to avoid all spicy foods, and to not engage into any sexual activity.
What is the procedure?
Each participant was “typed” based on their MHC.
The men were asked to wear a T-shirt for two nights and to keep the T-shirt in an open plastic bag during the day.
Two days later the women were asked to rank the smell of 7 T-shirts, each in a cardboard box with a smelling hole. The women were tested whenever possible in the second week after the beginning of menstruation, as women tend to be most odor-sensitive at this time.
3 of the 7 boxes contained t-shirts from men with MHC similar to the woman’s.
3 of the 7 boxes contained t-shirts from men with MHC dissimilar to the woman’s.
1 of the 7 boxes contained an unworn t-shirt to act as a control.
Alone in a room the women scored the odors of the t-shirts for:
Intensity (0-10)
Pleasantness and sexiness (0-10, 5=neutral)
What are the results?
Women scored higher the men with odors dissimilar to their MHC.
What is the conclusion?
This suggests that the MHC may influence human mate choice.
Tell me about the study of Wedekind.
Date: 1995
Aim: Whether one’s MHC (Major Histocompatability Complex) is related to sexual attraction or would impact it.
Participants:
Students of a university:
49 female
The women had to use a nose spray for 14 before the experiment → support the regeneration of the nasal mucous membrane.
44 male
They were given perfume-free detergent to wash clothes and bedclothes and perfume-free soap for showering.
They were asked to not use any deodorants or perfumes, to refrain from smoking tobacco or drinking alcohol, to avoid all spicy foods, and to not engage into any sexual activity.
Procedure:
Each participant was “typed” based on their MHC.
The men were asked to wear a T-shirt for two nights and to keep the T-shirt in an open plastic bag during the day.
Two days later the women were asked to rank the smell of 7 T-shirts, each in a cardboard box with a smelling hole. The women were tested whenever possible in the second week after the beginning of menstruation, as women tend to be most odor-sensitive at this time.
3 of the 7 boxes contained t-shirts from men with MHC similar to the woman’s.
3 of the 7 boxes contained t-shirts from men with MHC dissimilar to the woman’s.
1 of the 7 boxes contained an unworn t-shirt to act as a control.
Alone in a room the women scored the odors of the t-shirts for:
Intensity (0-10)
Pleasantness and sexiness (0-10, 5=neutral)
Results:
Women scored higher the men with odors dissimilar to their MHC.
Conclusion: this suggests that the MHC may influence human mate choice.
How do you link this study to the theory?
It studies the role of pheromones in mate selection, demonstrating that individuals are attracted to the scent of potential partners with different immune system genes, suggesting that pheromones play a role in enhancing genetic diversity through mate choice.
Evaluate the study.
This study has been successfully replicated by Jacob et al.
The theory is too reductionist → oversimplifies the behaviour of human mate selection by bringing it down to the MHC, ignoring cognitive and sociocultural factors.
Double-blind study → neither the researchers nor the participants knew which t-shirt they were being exposed to at any point of the study → minimise demand characteristics.
The results can’t be generalised → sample was limited to a specific age and culture.
When was Zhou et al conducted?
2014
What is the aim?
See the effect of AND and EST on heterosexual and homosexual men and women.
Who are the participants?
Four groups of healthy non-smokers
24 heterosexual males,
24 heterosexual females,
24 homosexual males &
24 homosexual or bisexual females.
What is the procedure?
They were presented with a point-light walker task (PLW) → a set of dots that move in a way that represent the properties of human motion.
They were asked to observe the stick figure in motion and identify its sex.
They did the task three days in a row at the sam time of day.
Throughout all this time they were exposed to androstadienone (AND) or estratetraenol (EST) or a control solution, all of them with cloves.
They performed the task only while they were smelling one o the solutions each day.
What are the results?
When heterosexual females and homosexual males were exposed to AND → higher rate of identifying the stick figure as male, than the control group.
AND had no significant effect on heterosexual males or lesbian women.
Smelling EST, respectively, had similar effect to heterosexual men → they thought it was a female stick figure.
The effect was not statistically significant in bisexual and lesbian women.
What is the conclusion?
AND and EST may have some effect on human sexual behaviour.
Tell me about the study of Zhou et al.
Date: 2014
Aim: See the effect of AND and EST on heterosexual and homosexual men and women.
Participants: Four groups of healthy non-smokers
24 heterosexual males,
24 heterosexual females,
24 homosexual males &
24 homosexual or bisexual females.
Procedure:
They were presented with a point-light walker task (PLW) → a set of dots that move in a way that represent the properties of human motion.
They were asked to observe the stick figure in motion and identify its sex.
They did the task three days in a row at the sam time of day.
Throughout all this time they were exposed to androstadienone (AND) or estratetraenol (EST) or a control solution, all of them with cloves.
They performed the task only while they were smelling one o the solutions each day.
Results:
When heterosexual females and homosexual males were exposed to AND → higher rate of identifying the stick figure as male, than the control group.
AND had no significant effect on heterosexual males or lesbian women.
Smelling EST, respectively, had similar effect to heterosexual men → they thought it was a female stick figure.
The effect was not statistically significant in bisexual and lesbian women.
Conclusion: AND and EST may have some effect on human sexual behaviour.
How do you link this study to the theory?
It investigates the role of pheromones in human behaviour, showing that exposure to certain pheromones can influence gender perception and sexual attraction, highlighting the subtle but significant impact of them on social and reproductive behaviours.
Evaluate the study.
Cause-and-effect relationship between the use of AND and EST and the rating of the stick figure
The study was counter balanced → different participants go through the same procedure, though in different way or order.
The study tried to be replicated but failed → the results may not be reliable, as the results of the replicated study were not significant.
The does of AND and EST that the participants were exposed to were a lot higher than what we as humans naturally secrete. → it is difficult to actually apply the findings to human behaviour.
