Hi, I'm Adriene, welcome to the salon.  This is mental_floss video and did you know that eye contact influences love?  In one 1989 study, researchers divided 72 undergraduates into male/female pairs, then had them stare into each others' eyes for two minutes.  After those two minutes, they experienced an increase in love and affection for the other student.  This was more than pairs who looked at each other's hands or counted the other person's blinks, and that's the first of many facts about the science of love that I'm gonna share with you today.

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A 2014 study conducted at the University of Rochester found that newlywed couples who watched five romantic comedies in a month and then discussed them were less likely to get divorced within the following three years.  In fact, the authors claim that doing so, "reduced the divorce and separation rate from 24 to 11%."

And contrary to popular belief, romantic comedies haven't been shown to make young people unrealistic about relationships.  A different experiment conducted one year earlier found that undergraduates who frequently watched them weren't more likely to believe in soul-mates, love at first sight, or the concept that love conquers all.

Though it's worth noting that according to one survey of 1500 Americans from diverse backgrounds, 2/3 of them believed in love at first sight.  

Interestingly, love at first sight might involve genetics.  Many animals, including fruit flies, have the ability to determine who to mate with based on genetic compatibility and some scientists believe that humans do the same thing, though it needs to be researched more.

And actually, people tend to marry people who have similar DNA to themselves.  One study from the University of Colorado looked at the DNA of 825 married couples.  The researchers found that the DNA of married people is more similar than the DNA of two strangers.  

One study published in 2013 showed that newlyweds probably knew whether or not their marriages would last.  Every six months for four years, newlyweds took a computer test in which a picture of their spouse quickly flashed on the screen, followed by a positive or negative word like 'awesome' or 'awful'.  Then they'd have to indicate whether the word was positive or negative.  Their reaction times were actually indicative of their relationship satisfaction.  Those who were able to identify the negative words faster reported more marital dissatisfaction at the end of the experiment.

Studies have shown that both straight men and women tend to speak in a lower voice when they're speaking to an attractive member of the opposite sex.  This surprised researchers who typically hypothesized that women would speak in a higher pitch in that context.

At the University of California in 2009, a study found that a romantic partner has a pain-reducing effect on women.  The researchers examined 25 undergraduates who'd been in a relationship with someone for at least six months.  They received mild burns and reported less pain when looking at a picture of their partner or holding hands with them, but really, they were burning them?  It's so disturbing.

Love might have some chemical similarities to Obsessive Compulsive Disorder.  One experiment measured serotonin levels in three groups: those who recently fell in love and reported thinking about the person for four hours or more every day, people with OCD, and a control group.  It turned out that the first two groups had 40% less serotonin in their blood than the control group.

Speaking of which, there's actually a disorder known as Relationship Obsessive Compulsive Disorder, or ROCD.  People diagnosed with ROCD tend to be enamoured with relationships, whether romantic or not, and spend a long time wondering whether their partner is "the one" and this is reflected in compulsions like loyalty tests.

Another thing relationships have been compared to, cocaine.  One 2010 experiment revealed that the brain on love and the brain on cocaine were very similar, both involving a huge release of dopamine.  

According to another 2010 study from Oxford University, falling in love is typically accompanied by losing two friends.  

The term 'sexual imprinting' describes a phenomenon that people tend to choose partners who have similar features and bone structures to their parents.  A concept that's supported by some studies.  Score one for Freud.

Moving on to less creepy things, one study from the 80s found that men who kissed their wives in the morning tended to have fewer car accidents and live longer.

According to research from Rutgers University in 2007, women who believe in gender equality are more likely to be in a relationship than women who don't identify as feminists.

A 2013 study out of Finland asked subjects to identify which areas of the body were associated with which emotions.  They found that people reported feeling love and happiness throughout the whole body, which was true across different cultures.  

Speaking of which, there are physical symptoms to love as well.  For instance, women's' eyes tend to dilate when they're looking at someone who interests them sexually.  

The immune system has also been shown to be important when it comes to attractiveness.  Women typically prefer men who have healthier immune systems, which is related to high-levels of testosterone.  Men with less powerful immune systems are rated as less attractive by women.

Studies show that in the first year of a romantic relationship, both men and women experience an increase in nerve growth factors.  This is why you might experience things like butterflies at the beginning of a relationship, but if the relationship goes on NGF stabilizes.  

Some studies have suggested that infidelity is genetic.  There's a gene known as DRD-4 and one 2010 study found that people who had the 7R+ variation of DRD-4 were more likely to report being promiscuous and unfaithful in relationships.  This applied to both genders.

It's also possible that cheaters just look different.  A 2002 study published in Evolution and Human Behavior had participants try to recall the faces of people who were labeled as cheaters or cooperators and it was easier for participants to recognize the faces of cheaters.  The researchers believed that cheaters might actually have different appearances, making them easier to remember.

In one study of 124 couples, the majority kissed by turning their heads to the right.  Only 44 couples went to the left.  The man who conducted the experiment believes this is a genetic trait, but that has yet to be proven.

Also, the active of kissing might have evolved for a reason.  Studies have shown that saliva contains testosterone and in other studies, men have indicated a preference for open mouth kisses, aka more saliva sharing.  Some scientists believe this is evolutionary.  A man is putting testosteroney saliva into a woman to stir up her sex drive.

Scientists have also ventured into the tricky subject of true everlasting love, like psychologist Barbara Fredrickson of UNC Chapel Hill.  She claims that love lasts due to micro-moments of positivity resonance, basically positive moments and emotions keep relationships going, but she states that you have these moments with everyone who makes you happy.  You can even fall in love with a complete stranger you meet, just for a second.

Finally, I return to our lovely salon to tell you that some scientists believe that love can last.  In 2009, researchers scanned the brains of a few new couples and a few couples who'd been together for 20 years after showing them pictures of their loved ones, and 10% of the older couples had similar chemical reactions to the younger couples.

Thanks for watching mental_floss video, which is made with the help of all of these nice people.  Again, I'm Adriene, sometimes I host CrashCourse Economics, which you can check out here.  Bye.