Thread by @Sheril_

Your votes overwhelming support a thread about The Science of Kissing. So let's get to it. 20 Things You Didn’t Know About Kissing:

1) Our lips are the body’s most exposed erogenous zone. Unlike in other animals, human lips are uniquely everted, meaning they purse outwardly.

2) Kissing is about more than bacterial exchange or romance. Our 1st experiences w love & security often involve lip pressure & stimulation through nursing or bottle feeding. This lays down neural pathways in a baby’s brain that later associate kissing w positive emotions.

3) Even Charles Darwin, the father of evolutionary biology, was fascinated by kissing across cultures. He discussed what he observed in his 1872 book The Expression of the Emotions in Man & Animals, concluding that the drive for humans to “kiss” in some form appears to be innate.

4) The first literary evidence for kissing dates back thousands of years to India’s Vedic Sanskrit texts. No word exists for “kiss” but there’s a reference to lovers “setting mouth to mouth” & a man “drinking the moisture of the lips” of a slave woman.

5) Kissing activates a v large part of the brain associated w sensory information bc we need to work to make sense of the experience in order to decide what to do next. Kisses send a whirlwind of neurotransmitters & hormones through our bodies that influence how we think & feel.

6) Dopamine, a neurotransmitter associated w desire & reward, spikes in response to novel experiences, which explains why a 1st kiss w someone new can feel so special. It involves in the ventral tegmental area of the brain, the same area affected by addictive drugs like cocaine.

7) One the most voyeuristic studies I found reported 2/3 of us turn to the right when kissing, which may mirror a head-turning preference observed in babies.

Yet kind of creepy: The scientist who determined this watched couples kiss in public places like airports & beaches. 👀

8) Evolutionary psychologists @SUNY found that 59% of men & 66% of women say they have ended a budding relationship bc a kiss didn’t go well. This may be, in part, due to subconscious clues a kiss reveals about our genetic compatibility. It's nature’s ultimate litmus test.

9) What about the rest of the animal kingdom? We see many similar behaviors in other species but we don't call it “kissing” bc we don't want to anthropomorphize & don’t know what motivates an animal. But it’s always about a socially significant connection.

10) This one's for @neiltyson who motivated this thread.

In July 2009, @NASAHubble captured this image of NGC 6302, aka the Butterfly Nebula. At 3,800 light years away, perhaps the galaxy's 1st kiss was made up of star stuff.

11) During a passionate kiss, our blood vessels dilate & we receive more oxygen to the brain. Our breathing can become irregular & deepen, our cheeks flush, our pulse quickens & our pupils dilate - which may be one reason so many of us close our eyes. [Image: Wim Delvoye]

12) Meet the sensory homunculus. It's like a brain's-eye view of the body where each part is sized according to how much space the brain gives to processing sensory information about it.

The lips & tongue are packed w sensitive nerve endings, helping us interpret our world.

13a) The major histocompatibility complex (MHC) is a group of genes that control how our immune system defends itself. When kids have more variation in MHC genes, their bodies may have an easier time recognizing invaders. So how do we ID a partner w a distinctly different MHC?

13b) Wedekind's famous "sweaty T-shirt experiment" found women are most attracted to the scents of shirts worn by men with MHC genes different from their own. And there's no better way to "sample" a partner's scent than getting into their "personal space" to kiss.

13c) One important note on this one though: Women on the birth control pill expressed the opposite preference & were more likely to favor scents of men w similar MHC genes. So it's possible these hormones may be changing our bodies & partner choices in more ways than we realize.

14) Kissing is also the most intimate human exchange. Remember that scene in Pretty Woman when Vivian (Julia Roberts) says she'll have sex w clients, but won't kiss them? Refraining from kissing has been historically common for prostitutes to keep emotions out of their work.

15) During the global pandemic, hygiene & disease are a necessary part of this story. 😱
So how dangerous is kissing? Although kisses expose us to bacteria & viruses, there are typically a greater number of dangerous germs transmitted during a handshake. 😎

16) During the Middle Ages, a kiss was a legal way to seal a contract. Men who didn't know how to read & write would draw an "X" & kiss the spot to make it legal.

We carry this on today in the way we continue to write "X" to signify a kiss.

17) Men produce more testosterone than women, but women are more sensitive to it. Since a man's saliva contains the hormone, scientists theorize that in heterosexual couples, open mouth kissing over weeks & months may enhance a female partner's libido.

17b) There hasn’t been much research on kissing. (Odd given it’s an extremely significant human behavior). There’s been even less considering the LGBTQIA+ community. 🏳️‍🌈🏳️‍⚧️

Our MEG (brain-scan) study included non-heterosexual participants & same-sex imagery journals.lww.com/neuroreport/Ab…

18) A woman's lips get noticed, in part bc they provide clues about her fertility. They swell at puberty & studies link full lips to higher levels of estrogen.

For at least 5,000 yrs, women all around the world have enhanced their lips using dyes, wine & lipstick.

19a) Studies in the US & Australia report women tend to value kissing itself more than men.

Women are most likely to describe kissing as a way to assess a new partner or monitor relationship status.

Men more often describe kissing as a way to induce sexual arousal.

But why?

19b) Psychologists theorize our diff kissing attitudes have to do w reproduction.

Women are born w all of the eggs we'll ever have & fertile a few days/month over a limited # of yrs.

Men produce sperm constantly & have fathered babies into their 90s. (Ramjeet Raghav at 96! ⬇️)

19c) From an evolutionary perspective, men have seemingly endless opportunities to pass on genes.

Women don't & must (traditionally) invest far more in pregnancy & motherhood.

So we have to be very selective choosing a partner & use clues from kissing to guide our decisions.

19d) What kind of clues influence how a woman feels about her partner?

Even though we're not consciously thinking about it, kissing involves the exchange of a great deal of information through body chemistry, smell & touch.

For one example, refer back to #13 in this thread. ⬆️

19e) A few folks have suggested 19c ⬆️ means it’s evolutionarily better to be male w more opportunities to pass on genes.

Not so fast.

Remember, there were no paternity tests until recently. For a v long time, only a woman could be sure a baby was hers (carried her genes). 🧬