Of course, love is a real emotion. Some say it is essential for life. But how does the emotion manifest? And what about sexual chemistry: what causes that spark to fly between two people, sometimes immediately? Can pheromones help a lonely heart to make the object of their attention love-struck? Is there any scientific basis for the success (or not) of dating websites? Why are humans the only species known to kiss?
This week, in the lead-up to Valentine’s day, these curiosities are on my mind. Let’s start the biology exploration with the topic of love.
Scientists who study the neurochemical basis of emotions believe that there are three stages to love, each with their own hormonal controllers:
Stage 1 – lust – ruled by testosterone and estrogen (the sexual hormones)
Stage 2 – attraction – controlled by dopamine, norepinephrine, and serotonin (those feel-good compounds)
Stage 3 – attachment – initiated by oxytocin (aka: the hormone thought to create the bond between mother and child; known to play a role in trust, empathy and generosity)
I would suggest a potential 4th stage – jealousy – which has recently been linked to oxytocin as well. And a potential 5th stage – infidelity – which has been linked to a genetic allele in some studies, and has also been linked to high levels of the hormone estradiol in women.
Pheromones, or chemical sexual signals emitted as odors, are often touted on the web and in marketing pitches as a sort of love potion – a magic bullet to enamour your paramour… but the science behind pheromones makes no such claims. About 50 years ago pheromones were discovered in moths, when it was observed that female moths produce the chemical bombykol which acts as a sex signal for male moths. Since then, pheromones, and the brain region that responds to them (the vomeronasal organ) have been identified in a multitude of species, but the ability of humans to detect pheromones with their vomeronasal organ has not yet been proven.
This is not to say that humans don’t experience a physiological response to the odor of a potential mate. Studies have been conducted to expose women to male underarm odorants, and this did cause an increase in sex hormones in the women’s circulation. In addition, studies in 2001 showed that humans exhibit a brain-response (measured by PET imaging) in response to synthetic sex hormones meant to mimic estrogen and testosterone. Definitive evidence remains to be collected.
Interestingly, many biology classes exhibit a potential role for human pheromones using this simple experiment: students each bring home a fresh tee-shirt and wear it to bed every night for a week – without showering or applying any scented products of any kind beforehand. Then back in the lab/classroom, the shirts are placed in plastic bags and given a labeling system to indicate if the shirt came from a male or female – but only the professor knows the labeling code. Students then rotate around the room sniffing the shirts, and guessing whether they came from a male or female. Students guess correctly more than 90% of the time on average.
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Many online dating sites today claim to use scientific principles or algorithms to match you to your mate. This week, the New York Times published an Op-Ed piece summarizing these claims, and planting questions about their scientific validity. Basically, several sites use mathematical algorithms to interpret data collected from personality tests, but no systematic study has been conducted to determine if these methods result in better love matches. Other sites use genetic testing to create a match…An excerpt:
Consider ScientificMatch.com, founded about two years ago, which aims to create romantic chemistry via genetic testing. The site, which matches people based on certain genetic markers for the immune system, takes its cue from studies showing that women are more attracted to the smell of men who have very different immune systems from their own. The site charges $1,995.95 for a lifetime membership — the lofty fee includes a cheek swabbing kit, DNA processing, a criminal and bankruptcy background check, as well as verification of age and marital status, the site says.
Then there’s Chemistry.com, started in 2006 by the dating giant Match.com. Helen Fisher, the biological anthropologist who developed Chemistry.com’s questionnaire, says the site is designed to predict compatibility based on traits of temperament like adventurousness, decisiveness or empathy. And it charges a premium for its services: about $50 for a one-month membership, compared with about $35 for Match.com.
But both ScientificMatch.com and Chemistry.com are refinements of an idea originally developed by eHarmony.com.
Founded in 2000 by a psychologist with experience in marriage counseling, eHarmony focuses on singles willing to invest time and to pay premium prices to find a long-term partner. People who register with the site fill out a long questionnaire that is intended to match people based on similarities in sociological variables like values, family background and social styles. Membership can cost up to $45.95 a month.
Finally, let’s explore the biology of the kiss. Kissing appears to be a behavior mainly enjoyed by humans. The lips contain many nerve endings and touch receptors, one of the most highly clustered areas of our body. And saliva is a highly chemical cocktail, including hormones like testosterone.
Biologists believe kissing may have evolved from our primate ancestors’ feeding behaviors, which often involved mouth-to-mouth feeding. And anthropologists believe kissing is a means for assessing a potential mate – anecdotal evidence certainly supports this, as anyone knows you may feel sexual chemistry with someone but after a kiss you may feel otherwise.
More about the Science of Love:
http://www.sciencedaily.com/releases/2009/11/091112095038.htm
More about the Science of Pheromones:
http://www.npr.org/templates/story/story.php?storyId=99473253
More about the science of online dating:
http://www.nytimes.com/2010/02/07/business/07stream.html?em
More about the biology of kissing:
http://www.scientificamerican.com/article.cfm?id=affairs-of-the-lips-why-we-kiss
http://www.sciencedaily.com/releases/2007/08/070830121629.htm
http://www.wired.com/wiredscience/2009/02/kissingscience/
image from cartoonstock.com
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Michael Steinberg
doctorwascher
Paul Hinrichs
Mary Elizabeth Williams
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Salon.com
Comments
Robin - I think you're totally right. Our ancestors (evolutionarily) certainly relied on their sense of smell more than we do, and clearly that part of our nervous system is delivering important messages - including about our mate (same sex or opposite sex).
Another interesting point raised here (Eva, Robin) is about the knowledge regarding the biology of same-sex relationships - although there are many initiatives to improve the diversity of human subjects in research studies, in my opinion there is still a majority of funding and data collection focusing on white, male heterosexuals. I hope I see this improve in my lifetime. (my post on marijuana and homosexuality does provide links to a few of the good studies on the biological basis of homosexuality.)
vzn - you're right, I remember reading that...I can't quite remember the specifics either.
Thanks, Linda~!
http://www.pnas.org/content/103/21/8269.long (you need academic access for the link).
There's tons of literature out there about it. It's not really my area but nevertheless interesting.
Searching 'pheromones homosexual' returns only 23 entries on PubMed, while 'pheromones human' returns 824. As I said above, most studies do not focus on homosexuals and it is a glaring inequality in science today. But I think recent policies are working to improve this situation.