Why Are Humans Ticklish?

iStock/andresr
iStock/andresr

Fabian van den Berg:

There are a few ideas about why humans experience ticklishness and there are also two kinds of tickling. One of them is a defense mechanism or warning sign that something moving is on you. Think parasites on your skin or ... no, don’t think about that. The fancy name for that is knismesis. This is the kind of tickling you feel when something soft brushes up against you. Usually, this type of tickling doesn’t make you laugh; It tends to give you goosebumps, and feel a bit uncomfortable.

Another aspect of tickling has to do with the specific spots that are ticklish. The fancy name for this one is gargalesis. This kind of tickling is more intense and leads to uncontrolled laughter. Gargalesis isn’t as straightforward as knismesis, and most likely serves some kind of social aspect and helps us bond.


Quora

There are specific spots that are ticklish in this latter way, and those are important for parents and children to form bonds. When we grow up those same spots are also erogenous zones, which help with mating, another social activity we engage in.

That these spots are also vulnerable areas on our bodies is probably no coincidence. Some experts think there is an aspect of tickling behavior meant to teach youngsters to protect their most vulnerable areas.

But other animals tickle, too. Our close cousin the chimpanzee tickles during play, though they make more of a panting, out-of-breath sound when they are laughing. They enjoy it, which they show by not leaving you alone afterward because they want you to keep going.

Elephants can be tickled as well, but my favorite is the rat.

A woman plays with her pet rat
iStock/Imagesbybarbara

There was a study where it was someone’s job to tickle rats (that must look amazing on your resume). The researchers in question were like, "Come tickle rats with me." Fun aside, this was serious research. It was known that rats make specific high-frequency noises when they play or have sex, noises of enjoyment (kind of like laughing). When they tickled the rats they made the same noises, indicating that the rats were enjoying being tickled, similar to the way humans do. It activates brain areas and pathways that also light up when humans experience joy (at least, the areas analogous to ours).

But a note must be made here: We are often quick to ascribe human emotions to animals, which can be dangerous. Animals like chimps and rats seem to enjoy tickling, so there’s reason to think they experience it in a positive way. But not all animals are like that—so experts aren't 100 percent sure they really like being tickled all that much. (Unfortunately, we can’t ask them.)

A tragic example of misinterpretation is the slow loris. These critters can be tickled, but they don’t like it. What humans interpret as enjoyment is actually fear, making the playful behavior in humans or primates literal torture for this cute-looking animal.

Tickling likely serves as a warning signal and training to protect ourselves. It has a secondary feature in humans, other primates, and rats it seems: to facilitate social bonding. But be careful who you tickle—not all animals experience the same enjoyment (some humans don’t like it either).

This post originally appeared on Quora. Click here to view.

What Do the Numbers and Letters on a Boarding Pass Mean?

iStock.com/Laurence Dutton
iStock.com/Laurence Dutton

Picture this: You're about to embark on a vacation or business trip, and you have to fly to reach your destination. You get to the airport, make it through the security checkpoint, and breathe a sigh of relief. What do you do next? After putting your shoes back on, you'll probably look at your boarding pass to double-check your gate number and boarding time. You might scan the information screen for your flight number to see if your plane will arrive on schedule, and at some point before boarding, you'll also probably check your zone and seat numbers.

Aside from these key nuggets of information, the other letters and numbers on your boarding pass might seem like gobbledygook. If you find this layout confusing, you're not the only one. Designer and creative director Tyler Thompson once commented that it was almost as if "someone put on a blindfold, drank a fifth of whiskey, spun around 100 times, got kicked in the face by a mule … and then just started puking numbers and letters onto the boarding pass at random."

Of course, these seemingly secret codes aren't exactly secret, and they aren't random either. So let's break it down, starting with the six-character code you'll see somewhere on your boarding pass. This is your Passenger Name Reference (or PNR for short). On some boarding passes—like the one shown below—it may be referred to as a record locator or reservation code.

A boarding pass
Piergiuliano Chesi, Wikimedia Commons // Public domain

These alphanumeric codes are randomly generated, but they're also unique to your personal travel itinerary. They give airlines access to key information about your contact information and reservation—even your meal preferences. This is why it's ill-advised to post a photo of your boarding pass to social media while waiting at your airport gate. A hacker could theoretically use that PNR to access your account, and from there they could claim your frequent flier miles, change your flight details, or cancel your trip altogether.

You might also see a random standalone letter on your boarding pass. This references your booking class. "A" and "F," for instance, are typically used for first-class seats. The letter "Y" generally stands for economy class, while "Q" is an economy ticket purchased at a discounted rate. If you see a "B" you might be in luck—it means you could be eligible for a seat upgrade.

There might be other letters, too. "S/O," which is short for stopover, means you have a layover that lasts longer than four hours in the U.S. or more than 24 hours in another country. Likewise, "STPC" means "stopover paid by carrier," so you'll likely be put up in a hotel free of charge. Score!

One code you probably don’t want to see is "SSSS," which means your chances of getting stopped by TSA agents for a "Secondary Security Screening Selection" are high. For whatever reason, you've been identified as a higher security risk. This could be because you've booked last-minute or international one-way flights, or perhaps you've traveled to a "high-risk country." It could also be completely random.

Still confused? For a visual of what that all these codes look like on a boarding pass, check out this helpful infographic published by Lifehacker.

Have you got a Big Question you'd like us to answer? If so, send it to bigquestions@mentalfloss.com.

Does Having Allergies Mean That You Have A Decreased Immunity?

iStock.com/PeopleImages
iStock.com/PeopleImages

Tirumalai Kamala:

No, allergy isn't a sign of decreased immunity. It is a specific type of immune dysregulation. Autoimmunity, inflammatory disorders such as IBS and IBD, and even cancer are examples of other types of immune dysregulation.

Quality and target of immune responses and not their strength is the core issue in allergy. Let's see how.

—Allergens—substances known to induce allergy—are common. Some such as house dust mite and pollen are even ubiquitous.
—Everyone is exposed to allergens yet only a relative handful are clinically diagnosed with allergy.
—Thus allergens don't inherently trigger allergy. They can but only in those predisposed to allergy, not in everyone.
—Each allergic person makes pathological immune responses to not all but to only one or a few structurally related allergens while the non-allergic don't.
—Those diagnosed with allergy aren't necessarily more susceptible to other diseases.

If the immune response of each allergic person is selectively distorted when responding to specific allergens, what makes someone allergic? Obviously a mix of genetic and environmental factors.

[The] thing is allergy prevalence has spiked in recent decades, especially in developed countries, [which is] too short a time period for purely genetic mutation-based changes to be the sole cause, since that would take multiple generations to have such a population-wide effect. That tilts the balance towards environmental change, but what specifically?

Starting in the 1960s, epidemiologists began reporting a link between infections and allergy—[the] more infections in childhood, [the] less the allergy risk [this is called hygiene hypothesis]. Back then, microbiota weren't even a consideration but now we have learned better, so the hygiene hypothesis has expanded to include them.

Essentially, the idea is that the current Western style of living that rapidly developed over the 20th century fundamentally and dramatically reduced lifetime, and, crucially, early life exposure to environmental microorganisms, many of which would have normally become part of an individual's gut microbiota after they were born.

How could gut microbiota composition changes lead to selective allergies in specific individuals? Genetic predisposition should be taken as a given. However, natural history suggests that such predisposition transitioned to a full fledged clinical condition much more rarely in times past.

Let's briefly consider how that equation might have fundamentally changed in recent times. Consider indoor sanitation, piped chlorinated water, C-sections, milk formula, ultra-processed foods, lack of regular contact with farm animals (as a surrogate for nature) and profligate, ubiquitous, even excessive use of antimicrobial products such as antibiotics, to name just a few important factors.

Though some of these were beneficial in their own way, epidemiological data now suggests that such innovations in living conditions also disrupted the intimate association with the natural world that had been the norm for human societies since time immemorial. In the process such dramatic changes appear to have profoundly reduced human gut microbiota diversity among many, mostly in developed countries.

Unbeknownst to us, an epidemic of absence*, as Moises Velasquez-Manoff evocatively puts it, has thus been invisibly taking place across many human societies over the 20th century in lock-step with specific changes in living standards.

Such sudden and profound reduction in gut microbiota diversity thus emerges as the trigger that flips the normally hidden predisposition in some into clinically overt allergy. Actual mechanics of the process remain the subject of active research.

We (my colleague and I) propose a novel predictive mechanism for how disruption of regulatory T cell** function serves as the decisive and non-negotiable link between loss of specific microbiota and inflammatory disorders such as allergies. Time (and supporting data) will tell if we are right.

* An Epidemic of Absence: A New Way of Understanding Allergies and Autoimmune Diseases Reprint, Moises Velasquez-Manoff

** a small indispensable subset of CD4+ T cells.

This post originally appeared on Quora. Click here to view.

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