Pheromones

Could your scent make you irrisistible to the opposite sex?  Online pheromone retailers claim that these airborne chemicals are key to sexual attraction, and wearing pheromone-laced perfumes will boost your sexual appeal.  But are these claims true?  Do human pheromones even exist?  We still can't say for sure, but here is what we do know.


Video Activity

Watch the video below on pheromones, and take notes on the following:

  • What are pheromones?  What are some examples of how pheromones influence animal behavior?

  • What's the difference between an ordinary scent and a pheromone?
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  • What are human pheromones such a mystery?
What are pheromones?

Pheromones are airborne chemical messengers released by the body (for instance, through sweat and urine).  Pheromones have physical or emotional effects on other members of the same species.  In animals, pheromones can carry all sorts of messages - they can warn others of nearby predators, for example. 

The animal pheromones that have garnered the most attention are sex hormones, used to notify other members of the species that a sexually active male or female is nearby.  In some animal species, a female releases pheromones to attract the attention of nearby males, who flock to her as soon as her scent is detected.  Its as if the pheromones are carrying the message, "Hey!  I'm here, ready to mate with you!" 

Although pheromones have been well documented in many animal species, whether or not pheromones exist in humans is still a matter of debate.  Compared to many other animal species, our sense of smell is far less developed, and we tend to rely on sight and sound far more than smell in most situations.  If humans do have pheromones, they may simply be a leftover from our earlier evolution, and may not play much role in our behavior.  On the other hand, there is some preliminary evidence that suggests that human pheromones do exist.  Read the following two studies on pheromones in humans, and consider whether it might be worth it to invest in a pheromone scent, after all.
Research: Savic et al   

Aim: Investigate whether human pheromones exist, and how they affect the brain

Procedure

  • The researchers exposed participants (24 men and women) to the smell of two chemicals, almost identical to the naturally produced sex hormones, testosterone and estrogen

  • As participants smelled the chemicals, their brains were scanned using a PET machine

​Results

  • A region of the brain called the hypothalamus become activated in the men only when they smelled the female hormone, and become activated in the women only when they smelled the male hormone

  • The hypothalamus is a part of the brain which is linked to sexual behavior, and is not normally activated by ordinary smells

  • In a follow up study, Savic found that the brains of homosexual men responded just like the brains of women - the hypothalamus of gay men lit up when they smelled the male hormone, but did not respond to the female hormone

Conclusion

  • This study suggests that sex pheromones do exist in humans, and they may influence sexual behavior

Evaluation

  • This was a well controlled laboratory experiment demonstrating a causal relationship between chemical scent (the IV) and activity in the hypothalamus (the DV)

  • The number of participants was quite small, so this study should be replicated with more people to confirm the results

  • This study measured changes in brain activity, not actual behavior.  It is not clear how these pheromones would influence behavior in the real world, if at all


Research: Zhou 

Aim: Investigate how sex hormones can alter perception

Procedure

  • The experiment involved 4 groups: heterosexual men, heterosexual women, homosexual men, and homosexual women

  • Participants viewed a walking human shape known as a "point light marker" (see image below).  The gender of the human shape is ambiguous - it is not clear if its male or female. Participants had to say whether they thought the human shape was male or female
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  • At the same time, unbeknown to the participants, the scent of either a male or female pheromone was released in the air (androstadienone, found in male sweat and semen, and estratetraenol, found in female urine)

Results

  • Participants responded to the pheromones of the gender they were attracted to when interpret the gender of the "point light marker"

  • For example, if straight women (or gay men) smelled the male pheromone, they tended to view the "point light marker" as male

Conclusion

  • Human pheromones do exist, and they seem to alert people to possible mating opportunities

Evaluation

  • A well controlled laboratory experiment, showing a causal relationship between the independent variable (pheromones) and dependent variable (perception of the "point light marker" as male or female)

  • There are several reasons to doubt the ecological validity of this experiment.  The level of pheromones used was many times higher than would be encountered in everyday life.  The pheromones came from areas of the body (semen, urine) that we wouldn't normally be exposed to when meeting someone for the first time.  Finally, identifying the gender of a "point light marker" is a highly artificial task.  Its not clear how these pheremones would influence real-world behavior, if at all 



Point light marker, similar to that used in the study by Zhou on pheromones
TOK Link

Do human pheromones even exist?  If they do exist, can they really influence sexual behavior?  The honest answer to these questions is - we simply don't know for sure.  Our knowledge of human pheromones is woefully incomplete.

You might find it surprising that our knowledge of pheromones is so lacking.  After all, with all of our modern lab methods and technology, shouldn't we be able to find out?

There are a number of reasons why reliable knowledge of human pheromones is so difficult to acquire.  Here are a few reasons why:

  • Complexity of human attraction: Why we feel attracted to one person - and not someone else - is remarkably complex.  It encompasses all five of ours senses, not to mention our culture, memories, and personality.  This makes it very difficult to isolate and measure the effect of just one factor - such as human pheromones - on attraction. 

  • Complexity of human scent. Your "odorprint" - the unique smell you give off - is made up of hundreds of unidentified chemicals, including bacteria (ex. in the armpits) that mixes with your bodily chemicals.  Furthermore, humans have over 400 odour receptors - and each odour receptor has genetic variants, meaning that each person processes odours differently.  Given this complexity, it is very difficult to test how just one chemical - such as a pheromone - could make a significant difference in attraction.  

  • Difficulty in replicating findings.  When a study produces new, startling findings, other scientists will try to replicate the original study to confirm the results.  In many cases, research studies on pheromones have not been successfully replicated.  But then how do we know if the original study was flawed, or the attempt at replication was flawed?



IB Psych Matters

Many dubious online vendors sell pheromones that can supposedly make you irrisistible to the opposite sex.  For one example, see www.truepheromones.com

  • Read the website of an online pheromone vendor.  What claims does the company make?  To what extent are these claims supported by science?

  • What would it take to convince you that human pheromones exist?  What sort of evidence would you need to see?

  • If human pheromones really can influence someone to have sex with you, is it ethical to purchase and use pheromones?  Explain why or why not
Checklist

  • I can define pheromones, and give some examples of how pheromones influence behavior in animals and (possibly) humans

  • I can explain the Aim, Procedure, Findings, and Conclusion of two research studies: Savic's study using PET scans, and Zhou's study using the "point light marker".  In additional, I can evaluate both research studies

  • I can critically evaluate the evidence for human pheromones, explaining why it is so difficult to produce certain knowledge regarding their existence
Quiz Yourself!

1.  In Savic's study, which part of the brain became more activate when pheromones of the opposite gender were released?

(a) hypothalamus

(b) amygdala

(c) hippocampus

(d) prefrontal cortex


2.  In Zhou's study, when heterosexual female participants were exposed to the female pheromone, what finding was observed?

(a) Females were more likely to rate the point light marker as female

(b) Females were more likely to rate the point light marker as male

(c) There was no change in ratings of the point light marker

(d) The point light marker was less likely to be rated as either male or female


3.  In evaluating both Savic's and Zhou's research, what points can be made?

(a) Both studies used experimental methods, and ecological validity was high

(b) Both studies used experimental methods, but ecological validity was low

(c) Both studies used correlational methods, but ecological validity was high

(d) Both studies used correlational methods, and ecological validity was low


4.  The relationship between someone's "odorprint" and attraction is very difficult to study.  What is NOT one of the reasons why?

(a) It is impossible to chemically isolate a human pheromone

(b) The human scent is made up of a large number of chemicals

(c) There are genetic variations in odor receptors that influence how odors are processed

(d) The effects of odor on attraction are also influenced by culture and memory




Answers

​1 - A, 2 - C, 3 - B, 4 - A