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.

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.

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Why Do We Celebrate Christmas on December 25?

If Jesus wasn't born on December 25, does this rule still apply?
If Jesus wasn't born on December 25, does this rule still apply?
Jon Tyson, Unsplash

Each December, Christians throw a collective birthday bash to celebrate the anniversary of Jesus’s arrival on Earth. But without a birth certificate—or any other official record of his actual birthdate—in existence, December 25 seems like an arbitrary day for all our Christmas traditions. So how did early observers choose it?

When Was Jesus Really Born?

Since the Bible doesn’t name a month or even a season for Jesus’s birth, historians have relied on other context clues to estimate when it occurred. Shepherds tend sheep in the Nativity story, which people often cite as evidence that Jesus was more likely born during the spring. Others argue that Israel’s mild winter temperatures allow sheep to graze even in December. According to Slate, it’s also possible that sheep set aside for religious sacrifices may have been given free rein, frigid night or not.

The Adoration of the Shepherds by Sebastiano Conca, 1720.J. Paul Getty Museum // Public Domain

One clue pointing specifically to December 25 comes from the story of Mary’s cousin Elizabeth, who approached old age without having given birth to any children. One day, her husband, a priest named Zacharias, was burning incense in the temple when the angel Gabriel appeared to him with good news: Elizabeth would bear a son. Early Christians guessed that Zacharias was probably in the temple for Yom Kippur, which they believed always took place on September 24 (it actually shifts year to year based on the Jewish lunisolar calendar). Nine months after September 24 is June 24, so they chose that as the birthdate—and feast day—of Elizabeth and Zacharias’s son, John the Baptist. When Gabriel later visited Mary to let her know that she’d bear a son, too, he mentioned that Elizabeth was in her sixth month of pregnancy. That means Jesus would’ve been conceived in late March, and born in late December—the night of December 24, to be exact, or the early hours of December 25.

Another theory suggests that Christians arrived at December 25 based on an ancient Jewish idea that prophets die on their birthday. During the 3rd century CE, theologists like Tertullian and Hippolytus dated Jesus’s crucifixion to March 25, since it happened around Passover. But to Sextus Julius Africanus, it was less about when Jesus was born and more about when he first came to Earth; in other words, he believed Jesus’s death and conception coincided on March 25, and thus his birth occurred on December 25 [PDF].

The Early History of Christmas

Even if Zacharias was in the temple on September 24, Gabriel did visit Mary exactly six months later, and Jesus was born right on his due date, it’s still possible that we celebrate Christmas on December 25 for a different reason altogether.

While 3rd-century Christians were busy worshiping the Son of God, some of their pagan counterparts were busy worshiping the Sun God. In the 270s, Roman emperor Aurelian popularized the cult of Sol Invictus, or “The Unconquered Sun,” whose feast day was celebrated on December 25. According to John Carroll University history professor Joseph F. Kelly, other Romans revered a Persian god, Mithra, whose feast day also may have fallen on December 25. There was also Saturnalia, an annual Roman festival that ran from December 17 to December 23. In short, many ancient Romans were well-accustomed to celebrating something in late December by the time Christianity entered the mainstream.

A painting of Saturnalia festivities by Antoine Callet, 1783.Themadchopper, Wikimedia Commons // Public Domain

That happened during Constantine’s rule over Rome in the early 4th century. In 313, Constantine and his fellow ruler Licinius issued the Edict of Milan, which basically legalized Christianity and condemned the ongoing persecution of anyone who practiced it. Constantine was a devout Christian himself, and he spent the rest of his reign spreading the religion throughout the empire. The first known record of December 25 as Jesus’s official birthday is from 336, the year before Constantine died. Because it’s mentioned in a volume containing other important religious dates, some have assumed that a celebration probably occurred on that day, and 336 is often cited as the first known “Christmas.”

Whether Christians celebrated Christmas on December 25 before 336 may forever be unknown, but we do know that the custom quickly caught on (spending the holiday watching A Christmas Story marathon wouldn't come until much later). By the end of the 4th century, Christian bishops were holding Christmas Mass all over Rome, and pagan festivals soon fell out of fashion. The fact that Christmas essentially replaced those earlier December traditions could be a coincidence, but some believe it was by design: Since Romans were already primed for parties on December 25, the Church could’ve been trying to co-opt a built-in subscriber base.

In summary, the origins of Christmas are just as subject to interpretation as Jesus’s actual birthdate—so feel free to play Christmas music whenever you want.

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