The smell of friendship

A topic I covered in my intro to biology classes was the phenomenon of pheromones.

A pheromone is a chemical secreted by one individual that causes a behavioral change in another member of the same species.  There's a great variety -- sex pheromones (which causes the behavior you see in male dogs when a female dog goes into heat), alarm pheromones (such as the "attack" chemical released by killer bees that causes swarming), territorial pheromones (such as urine marking in wolves), and so on.  They're biochemical signals; much the way hormones signal between organs, pheromones signal between organisms.

This inevitably led to the question, "Do humans have pheromones?"  The answer is, "Probably, but it's hard to demonstrate conclusively."  Certainly, the "pheromonal" perfumes and colognes you've probably seen ads for are ripoffs; there is no evidence that there's anything you could add to a perfume that would act as an aphrodisiac.  (For some reason, I've mostly seen ads for this stuff in science magazines.  Maybe they think we nerds need all the help we can get in the romance department, I dunno.)

One of my AP Biology students years ago got interested in the topic of attractant pheromones, and designed a clever experiment to see if he could detect an effect in humans.  He had a bunch of volunteers agree to the following protocol: (1) shower first thing in the morning; (2) use odorless soap, shampoo, and deodorant, and don't put on any scented products; (3) don't eat any food that could change your body odor, such as garlic, curry, or asparagus; and (4) wear a plain white t-shirt (provided by the researcher) for an entire day, then seal it in a ziplock bag at the end of the day.  He then took the collected t-shirts (I think there were about twenty in all) and got a bunch of students to smell them, and rank them best-to-worst for odor.

[Image licensed under the Creative Commons Lateiner, T-shirt-2, CC BY-SA 3.0]

The results were pretty interesting.  There was a tendency for people to rank higher t-shirts that had been worn by volunteers of their preferred gender.  (There weren't any bisexuals in the test sample; maybe we think everyone smells good, I dunno.)  The most interesting part was that between the t-shirt wearing group and the t-shirt smelling group, there were a couple of pairs of siblings -- and they ranked their siblings as smelling terrible!

Curious results, which I was immediately reminded of when I stumbled on some research out of the Weizmann Institute of Science in Israel which showed there might be a pheromonal aspect not only of sexual attraction, but of friendship.

The procedure they followed was remarkably similar to my student's, if considerably more rigorous and technical.  They recruited twenty pairs of people who reported that they were friends, and further, had "clicked immediately" -- a phenomenon I think we can all relate to.  (It's equally common to meet someone you dislike immediately -- but that'd have been a lot harder to study.)  They then did a similar t-shirt wearing protocol, but at the end of the day, instead of having someone smell it, they used an electronic volatile chemical analyzer to determine what odor-carrying substances there might be in the shirts.

What they found was that the chemistry of the sweat left behind in the t-shirts was remarkably similar between people who were friends.  Further -- and even wilder -- they then had the volunteers pair up with same-sex strangers from the research group, eventually testing all possible same-sex pairings, and had them stand in close proximity for two minutes (in silence).  They then were asked to rank the person from 1 to 100 in terms of how comfortable they were, whether they felt a connection, and whether they'd be interested in meeting the person again.

Across the board, the more similar the pair's sweat chemistry, the higher the rankings were.  "The finding that it could predict clicking by body odor similarity alone—this was really cool," said study co-author Inval Ravreby.  "We were really excited to find this."

The researchers did admit that the effect was small (although statistically significant) and there was a lot of overlap in the data, but the fact that there's a trend at all is pretty amazing.  Human behavior is complex and multifaceted, and it's amazing how much of it is due to subliminal cues.  Despite our generally high opinions of our species, we're still animals -- and we interact with each other not only in human-specific ways but in the more instinctual ways other animals use.

Now, I'm not suggesting that you should try to find friends by walking up and sniffing people.  But maybe that feeling of an instant connection we sometimes have is more due to our sense of smell than it is any kind of cognitive assessment.

Think of that the next time you're having lunch with your best friend.

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The case of the telepathic trees

In my AP Biology class, we were discussing a peculiar phenomenon in certain plants; when under attack by herbivores, some species seem to be able to signal nearby members of the same species, who then respond by secreting noxious chemicals that repel the attackers.  This response has been observed in sagebrush, clover, a species of African acacia, and several others.

One of my students asked how that communication was accomplished.  I replied that it was all done by volatile chemical signals -- the attacked plant produces something like an animal pheromone, which then moves via the air to the surrounding plants.  The binding of that signal chemical onto receptors in the nearby individuals initiates synthesis of nasty-tasting compounds that discourage the herbivores from chowing down.

"If that chemical could be synthesized," one student asked, "could this be an easy and low-impact way of controlling plant pests?"

"That's a great idea," I said.  "It would depend on whether the specific signal chemical has been isolated."  And not knowing whether it had been, I started to do a little research.

A quick Google search turned up a number of sites describing reputable, peer-reviewed science (and it turns out that in some cases, they know what the signal is, and in others they appear not to).  So far, so good.  But then I noticed that about half of the hits I generated suggested a different explanation -- the plants were engaging in mental telepathy.

In fact, one unintentionally hilarious site, Psychobotany, goes into great detail about the possibility of humans telepathically communicating with plants (or vice versa).  As evidence that this might be possible, it dredges up the tired old pseudo-experiment by Clive Backster, who in the 1960s attached a polygraph machine to a plant, and threatened to hurt the plant, and the polygraph machine went crazy.  (The site conveniently doesn't mention that because of the amazing claims and the simplicity of the experimental design, Backster's experiment has been redone about 10,000 times since he first published, and nobody has ever been able to replicate his results.)

I find it maddening how quickly people want to leap to a supernatural explanation when someone reports something odd.  Richard Dawkins calls this the "Argument From Incredulity;" the world is weird, wonderful, amazing, and I don't have a ready explanation for what I'm seeing, therefore it must be __________.  Fill in the blank with your favorite paranormal explanation -- ESP, aliens, ghosts, spirits, god, the devil, etc. etc. etc.  Scientists are frequently accused of arrogance -- "You think you're so smart, you think you have all the answers."  In reality, the opposite is true.  If you're not comfortable with being in a state of ignorance, you won't last long in science, because the first thing you discover when you go into science is how little we actually are certain of.  This, to me, is one of science's strengths as a model; presented with anomalous data, a good scientist is perfectly willing to suspend judgment, indefinitely if need be.  Only a theory that explains all of the available data is good enough, and even then, there's a tentativeness about good science -- a sense of, "well, this is what we think now, but things could change if we get new information."  As Albert Einstein once said, "A thousand experiments could never prove me right, but one could prove me wrong."

The supernatural explanations, on the other hand, strike me as cheap cop-outs.  If you call plant communication "botanical telepathy" you don't have to go any further; you can sit there and enjoy your little mystical shiver up the spine, and you're all done.  There's no need to provide a mechanism, to look for details of how such a thing might be accomplished.  You've made your pronouncement about how the world works, and there it ends.

And in contrast with science, which shifts its stance if contrary data is found, supernatural explanations are notorious for clinging on like grim death even in the face of mountains of evidence.  The Psychobotany people even cite the study done with pheromonal communication in sagebrush, but oddly, they neglect to mention that the effect went away when the researchers placed plastic bags over the sagebrush plants.  This result brilliantly supports the chemical signal hypothesis, but is a little hard to explain if you buy telepathy.  Does plastic block Psychic Energy Rays, or something?

Myself, I have no problem with Not Knowing Stuff.  This sometimes bothers my students.  When I'm asked about things for which science has yet to find evidence, but which can't be ruled out on a theoretical basis -- things like alien visitations, Bigfoot, and life after death -- my answer is, "the jury's still out on that one."

"Well, do you believe in it?" they often ask.

My response is that I neither believe nor disbelieve in anything without sufficient evidence, or at least a strong logical argument one way or the other.  In the absence of either -- for instance, in the case of Bigfoot, where there's no particular biological reason that it's impossible, but there's also never been any hard evidence -- I am completely comfortable with adding that to the big old pile of stuff I don't know about.

On the other hand, in the case of the telepathic trees -- I'm pretty confident about that one.  "Psychobotany," my ass.  I think this time it's Science 1, Woo-woos 0.

Her tears, like diamonds on the floor

Crying is one of the weirdest biological phenomena.  Try to think about it from a non-human perspective, as if some benevolent alien scientist came to earth to study humanity.  So picture yourself being interviewed by the scientist, as you are clearly one of the more intelligent native life-forms:

Dr. Xglork:  "So, this crying thing I've heard of.  What is 'crying' and why do you do it?"

You:  "Well, when humans get sad, they start breathing funny, in little fits and starts, and water comes from their eyes."

Myself, I think that our Dr. Xglork would be justifiably mystified at how that sort of reaction makes any sense.  "How does that make you feel better?" he'd probably ask, looking at you quizzically from seven of his twelve eyes, while making notes on a clipboard held in his tentacles.

And yet, it does, doesn't it?  I'll admit, I cry easily.  Somehow guys aren't supposed to be that way, but there's no use denying it.  I cried my way through the last third of The Return of the King, embarrassing my older son to the point that for two years after that he refused to sit next to me in the theater.  I've cried over songs, television shows, and books (I almost had to wring out my friend's copy of Marley and Me before I could return it).

And after you cry, you feel better.  You don't look better, unless you somehow find red eyes and a snotty nose sexy; but you do somehow feel more relaxed and centered.  This universal reaction led scientists to surmise that crying was doing something to the levels of chemicals in the blood, so they did a study in which volunteers were put in a variety of situations that made them cry, and were asked to collect their tears in a vial.  Some were just exposed to irritants, like onions; others were shown sad movies (I'd have needed a bucket).  Then they chemically analyzed the tears to see if there were differences.

And there were.  There were proteins present in the tears we cry when we're sad that are absent in the ones we cry because our eyes are irritated.  This implies an interesting function for crying -- ridding our blood (and therefore presumably our brain as well) of chemicals which are making us feel sad or stressed.  Crying therefore does serve an important function, as our emotional reaction afterwards would suggest.

And just a few days ago a new study became public that sheds even more light on the whole thing.  Friday's issue of the journal Science included an article by Noam Sobel of Israels' Weizmann Institute of Science.  Sobel and his team took the crying study one step further -- they wanted to find out the effects of crying not on the person who was doing the crying, but anyone nearby.

So they collected tears from female volunteers (it being difficult, according to Sobel, to get a guy to cry in a lab; maybe they should have flown me over there).  They then allowed male volunteers to smell the vials of tears, including some vials of saline solution (as a control).

The team's hypothesis -- that there was a pheromone in tears that elicited empathy in others -- turned out to be incorrect.  When shown photographs of sad or tragic events, the men who'd smelled the actual tears didn't rate them as any sadder, or their emotional reaction to them as any stronger, than the guys who'd smelled the saline solution.

The real surprise came when the guys in the study were asked to rate various women's photographs for sexual attractiveness, and they found out that the guys who'd smelled the tears rated all the photographs lower than the guys who'd smelled saline did.  And -- most amazingly -- when given a quick saliva test for testosterone levels, the guys who'd smelled the tears showed lower levels of testosterone than the control group, and when given an MRI, lower activity in the parts of the brain associated with sexual arousal.

So crying, it seems, has a chemical "not NOW, honey!" feature.  This whole thing opens up a variety of questions, however.  First, it makes you wonder how the writers of Seinfeld ever came up with the idea of "make-up sex."  Second, do male tears have a pheromone as well?  Apparently Sobel's team has now found a "good male crier" and is going to see if there's any kind of reciprocal reaction in women -- and I'll bet there is.  And third, and most important -- does this explain the phenomenon of the "chick flick?"  I'll leave that one for you to decide.