exam 1 pt2 Flashcards
MHC & Smell: Evolutionary Argument
women
Reproductive success: Women
Getting pregnant costs women a lot
Women may be more attuned to picking reproductive opportunities that may produce offspring that are immunologically fit and more likely to survive
MHC & Smell: Evolutionary Argument
Men lack a more sensitive sense of smell that might distract them from taking advantage of a reproductive opportunity
Women may use it to select mates
When a guy’s a genetic mismatch for you, the funny smell may well be your body sending up a red flag
MHC Compatibility & Infidelity
Garver-Apgar et al. (2006)
Asked 50 long-term couples a series of questions:
How attracted were they to their partners?
How satisfying were their sex-lives?
How much did they fantasize about having other sexual partners?
Have they had any affairs?
If so, when and how often?
MHC Compatibility & Infidelity (Findings)
The average couple has 20 % of their MHC variants in common
The more MHC variants women shared with their partners:
The less sexually attracted she was to him
The more she rejected his sexual advances
The more she fantasized about other men
The less aroused she felt when having sex with him
MHC Scent Preferences & the Pill
Want to hear something wacky that happens when you’re on birth control pills?
Your scent preference inverts and you actually PREFER the smell of men whose MHC’s are SIMILAR to your own!
Researchers uncertain why normal preference pattern get reversed
Likely has something to do with the lack of hormonal fluctuations ovulating women normally experience (you don’t ovulate if you’re on the pill)
What about Pheromone Sprays?
There’s a pretty booming industry selling “pheromone” sprays
Producers claim will “unleash your lover’s animalistic side!”
Given that female response to male testosterone derivatives is based on MHC, it doesn’t seem realistic to expect any one smell to do the trick
Bacterial By-Products
Microbes in sweat glands break down sex-hormones and MHC-related proteins
The resulting body-odor is at least partly bacterial by-product The musky smell of male sweat comes from the bacterial breakdown of androstenone
Enter the Vomeronasal Organ (VNO)
What mammals use to detect pheromones
Two pits located in the nasal septum between the nose and the mouth
(PEOPLE HAVE THEM TOO)
How PHERONMONES WORK
1-Our bodies naturally secrete fluids through glands in our body that contain natural pheromones
2-The vomeronasal organ detects the pheromones and sends a signal to the olfactory nerves.
3- the olfactory nerves stimulates the hypothalums in the cortex of the brain which stimulates emotion
4-The pheromone scent triggers illcit emotions in the hypothalmus such as attraction , sexual desire and arousal
Smelly T-Shirt Studies
A series of studies has been conducted in which women have to sniff t-shirts
T-Shirts have been worn for several days by anonymous men
Women are asked to identify which ones smell (relatively) appealing
Some studies actually have the men run on treadmills and sweat a lot before collecting the T-shirts
Smelly T-Shirt Studies To produce the men’s most pure, untainted scents, during the study they aren’t allowed to:
wear deodorant or cologne use scented soap eat food that contains garlic, cumin or curry smoke drink alcohol have sex
Smelly T-Shirt Studies Across these studies, a pattern emerges
Women prefer the body odor of men who have MHC variants that are mostly different from their own
When the researchers include a male relative among the men (father, brother), the women rate those t-shirts as the worst.
Why?
MHC & Smell
Interestingly, men are far less sensitive to smells than are women
In fact, they are largely unable to detect MHC variants in odor
Unappealing MHC-related body odor is a deal-breaker for many women
Most guys are oblivious to it
Why?
MHC & Smell: Evolutionary Argument
Women appear attracted to the smell of men who only share few MHC variants
Human women aren’t alone in this preference
It’s well documented in birds, fish, and numerous other mammals
The bias appears to be about reproduction and species survival
MHC & Smell: Evolutionary Argument pt2
Reproductive success: Men
Getting women pregnant doesn’t cost men a lot
Men have the best chance of passing on their genes if they jump at every reproductive opportunity they get