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ลำดับตอนที่ #37 : Special Article : Valentine ; Why do we kiss
When you
think about it, kissing is strange and a bit icky. You share saliva with
someone, sometimes for a prolonged period of time. One kiss could pass on 80
million bacteria, not all of them good.
Yet everyone surely remembers their first kiss, in all its
embarrassing or delightful detail, and kissing continues to play a big role in
new romances.
At least, it does in some societies. People in western societies
may assume that romantic kissing is a universal human behaviour, but a new analysis suggests that less than half of
all cultures actually do it. Kissing is also extremely rare in the animal
kingdom.
So what's really behind this odd behaviour? If it is useful, why
don't all animals do it – and all humans too? It turns out that the very fact
that most animals don't kiss helps explain why some do.
According to a new study of kissing preferences, which looked at 168 cultures from
around the world, only 46% of cultures kiss in the romantic sense.
Previous estimates had put the
figure at 90%. The new study excluded parents kissing their children, and
focused solely on romantic lip-on-lip action between couples.
Many hunter-gatherer
groups showed no evidence of kissing or desire to do so. Some even considered
it revolting. The
Mehinaku tribe in Brazil reportedly said it was "gross".
Humans lived in hunter-gatherer groups for most of our existence,
until the invention of farming around 10,000 years ago. If modern
hunter-gatherer groups do not practice romantic kissing, it is possible that
our ancestors did
not do so either
However we cannot be certain of this, as modern hunter-gatherer
groups do not live in the same ways as the ancestral hunter-gatherers, because
their societies have changed and adapted in the meantime.
Regardless, the study overturns the belief that romantic kissing
is a near-universal human behaviour, says lead author William Jankowiak of the University of Nevada in
Las Vegas. Instead it seems to be a product of western societies, passed on
from one generation to the next, he says.
There is some historical evidence to back that up.
Kissing as we do it today
seems to be a fairly
recent invention, says Rafael Wlodarski of the
University of Oxford in the UK. He has trawled through records to find evidence of how
kissing has changed.
The oldest
evidence of a kissing-type behaviour comes from Hindu Vedic Sanskrit texts from
over 3,500 years ago. Kissing was described as inhaling each other's soul.
In contrast, Egyptian hieroglyphics picture people close to each other rather than
pressing their lips together.
So what is going on? Is kissing something we do naturally, but
that some cultures have suppressed?
Or is it something modern humans have invented?
We can find some insight by looking at animals.
Our closest relatives,
chimpanzees and bonobos, do kiss. Primatologist Frans de Waal of
Emory University in Atlanta, Georgia, has seen many instances of chimps kissing and hugging
after conflict.
For chimpanzees, kissing is a form
of reconciliation.
It is more common among males than females. In other words, it is not a
romantic behaviour.
Their
cousins the bonobos kiss more often, and they
often use tongues while doing so. That's perhaps not surprising, because
bonobos are highly sexual beings.
When two
humans meet, we might shake hands. Bonobos have sex: the so-called bonobo
handshake. They also use sex for many other kinds of bonding. So their kisses are not
particularly romantic, either.
These two
apes are exceptions. As far as we know, other animals do not kiss at all. They
may nuzzle or touch
their faces together, but even those that have lips don't share saliva or purse and smack their
lips together. They don't need to.
Take wild boars.
Males produce a pungent smell that females find extremely attractive. The key
chemical is a pheromone called androstenone that
triggers the females' desire to mate.
From a female's point of view this is a good thing, because
males with the most androstonene
are also the most fertile.
Her sense of smell is so acute,
she doesn't need to get close enough to kiss the male.
The same is true of many other mammals. For example, female hamsters emit a pheromone that
gets males very excited. Mice follow similar chemical traces to help them find
partners that are genetically different, minimising the risk of accidental incest.
Animals often release these pheromones in their urine.
"Their urine is much more pungent," says Wlodarski. "If there's urine present in
the environment they can assess
compatibility
through that."
It's not just mammals that have a great sense of smell. A male
black widow spider can
smell pheromones produced by
a female that tell him if she has recently eaten. To minimise the risk of being
eaten, he will only mate with her if she is not hungry.
The point
is, animals do not need to get close to each other to smell out a good
potential mate.
On the other hand, humans have an atrocious sense of smell, so we benefit from
getting close. Smell isn't the only cue we use to assess each other's fitness, but studies have
shown that it plays an important role in mate choice.
A study
published in 1995 showed that women, just like mice, prefer the smell of men who are
genetically different from them. This makes sense, as mating with someone
with different genes is likely to produce healthy offspring. Kissing is a great way to get close
enough to sniff out your partner's genes.
In 2013, Wlodarski examined kissing
preferences in detail. He asked several hundred people what was most
important when kissing someone. How they smelled featured highly, and the
importance of smell increased when women were most fertile.
It turns out
that men also make a version of the pheromone that female boars find attractive. It
is present in male sweat,
and when women
are exposed to it their arousal
levels increase slightly.
Pheromones are a big
part of how mammals chose a mate, says Wlodarski, and we share some of them.
"We've inherited all of our biology from mammals, we've just added extra
things through evolutionary time."
On that
view, kissing is just a culturally acceptable way to get close enough to
another person to detect
their pheromones.
In some cultures, this sniffing behaviour turned into physical lip
contact. It's hard to pinpoint
when this happened, but both serve the same purpose, says Wlodarski.
So if you want to find a perfect match, you could forego kissing and start
smelling people instead. You'll find just as good a partner, and you won't get
half as many germs. Be prepared for some funny looks, though.
VOCABULARY
Preferences (n.)
the fact that you like something or someone more than another thing or
person:
estimates (v.)
to guess or calculate the cost,
size,
value, etc. of something:
hunter-gatherer
(n.)
a member of a society that lives by hunting and collectingwild food, rather than by farming
revolting
(adj.)
"gross". (adj.)
Fairly (adj. adv.)
more than average, but less than very:
used to emphasize figurative expressions that describe what people or objects are doing:
If you do something fairly, you do it in a way that is
right and reasonable and treats people equally:
Trawl (v.)
to search among a large number or many different places in order to find people or informationyou want:
hieroglyphics
(n.)
a system of writing that uses pictures instead of words, especially as used in ancient Egypt
suppressed
(v.)
to end something by force:
to prevent something from being seen or expressed or from operating:
instances (n.)
a particular situation, event, or fact, especially an example of something that happens generally:
(v.)
to give something as an example:
reconciliation
(n.)
a situation in which two people or groups of peoplebecome friendly again after
they have argued
the process of making two
opposite beliefs,
ideas,
or situations agree
bonding (n.)
the process by which a close emotional relationship is developed:
nuzzle (v.)
to touch,
rub,
or press something or
someone gently and/or in a
way that shows your love,
especially with the head or nose,
usually with small repeated movements:
purse (n.)
a small container for money,
usually used by a woman
the total amount of
money that an organization or government has available for spending:
an amount of
money that is offered as
a prize in a sportscompetition:
(v.)
to bring your lips tightly together so that they form a rounded shape, usually as an expression of disapproval:
acute (Adj.)
If a bad situation is acute, it causes severe problems or damage
An acute pain or
illness is one that quickly becomes very
severe:
used to describe intelligence, senses,
etc. that are very good, accurate, and able to
notice very small differences
An acute angle is
less than 90 degrees.
(n.)
a sign that is written above a letter in some languages, showing you how to pronounce the letter:
emit (v.)
to send out a beam, noise, smell, or gas:
traces (v.)
to find the origin of something:
incest (n.)
sexual activity involving people who are closely related and not legally allowed to marry:
pungent, (adj.)
A pungent smell or taste is very strong, sometimes unpleasantly strong
Pungent speech or writing is very strongly felt:
assess (v.)
to judge or decide the amount, value, quality, or importanceof something:
compatibility (n.)
the ability of machines, especially computers, or computer programs to work successfully with other machines or programs:
atrocious
(adj.)
cue (n.)
a signal for someone to do something:
offspring
(n.)
fertile (adj.)
Fertile land can produce a large number of good qualitycrops.
Boarsn (n.)
a male pig kept for breeding on a farm, or a type of wild pig
sweat (n.)
] the clear, salty liquid that you pass through your skin:
Arouse (v.)
to cause someone to have a particular feeling:
to cause someone to feel sexual excitement
detect (v.)
to notice something that is partly hidden or not clear, or to discover something, especially using a special method
to discover something, usually using special equipment
pinpoint (v.)
to find out or say the exact position in space or time of something:
to discover or describe the exact facts about something:
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