Why Laughter and Humor Evolved (my guess)
Laughter evolved because it provides quick relaxation after
removing a possible threat, thus facilitating bonding between
people who have collectively removed the threat, leading them
to collaborate more in the future. Humor exploits this response
by setting up and then quickly removing perceived threats, such
as the surprise endings of jokes.
Laughter to Facilitate Bonding with Compatible Bandmates
Imagine that you're roaming the savannah with three fellow
evolving humans, and a snarling leopard suddenly leaps out and threatens
you. You're terrified, but the four of you working together manage to drive
the leopard off. Due to your successful teamwork, it would probably be a
good idea to continue hanging out with this particular crew, since you
apparently work well together and can help each other survive and
reproduce. Continuing this collaboration would be more likely if you were
to emotionally bond with your teammates. Unfortunately, at the moment you're
too rattled to bond effectively. Bonding requires relaxation so that
you're no longer "on guard" and can open up to others.
You could just wait a while until you've gradually become relaxed
again, but by then your team likely will have separated.
And you're more inclined to bond with them while the image
of your combined success is still vivid.
It would be handy if you were able to relax very quickly so that you
could bond while the team is still together and celebrating your
triumph. A few slow, deep breaths would help, but right now
you're too excited and your chest muscles are too tensed up for that
to happen naturally. Fortunately, natural selection has come up with
a response that causes you to quickly relax in situations like this,
where bonding is important. It's known as laughter.
The Mechanics of Laughter
Laughter forces you to exhale deeply, by triggering a series of
short, uncontrolled, and forceful exhalations. It also blocks your
trachea between these exhalations to prevent you from inhaling in the
meantime, until you have exhaled fully. When the forced
exhalations finally allow you to inhale again, a deep inhalation to
recover completes an involuntary deep and slow breath,
resulting in relaxation.
On chasing the leopard off, you will likely find yourself laughing
in glee as the threat has suddenly gone away, leading you to
quickly relax and bond with your teammates.
Most laughter is also quite audible as well, though vibrating your
vocal chords is not necessary to force slow, deep breaths. Perhaps
someone else's audible laughter is a clear signal to you that
they are having an uncontrolled (and therefore sincere)
inclination to bond with you. This removes any worry that you might
have that they may be trying to con you by just acting like they
like you, and the sudden relief can lead you to laugh yourself.
This makes laughter "contagious".
In addition to deep breathing, your leg muscles become spastic during
laughter. This can cause you to stagger into your comrades, where the
direct skin contact further intensifies the bonding effect.
Laughter Results Whenever a Possible Threat Suddenly Goes Away
Laughter lets you bond with others when you have collectively removed a
threat, thereby increasing your tendency to band together. This
increases your survival odds, so the laughter response has been
selected for in this type of situation. And because natural selection often
over-generalizes as it stumbles onto responses that happen to increase
the reproductive rate, in this case it has generalized the laughter
response to be triggered by the relief that you feel any time a
possible threat has suddenly been revealed as no problem.
How Humor Removes a Possible Threat Via Surprise
Laughter is commonly associated with humor, which has little to do
with driving off leopards or other threats. Humor is actually just one
type of stimulus that induces laughter, and it hooks into the rule of the
suddenly removed threat in various ways. One way is through surprise.
(Many people have noted that much humor involves a surprise.) Any surprise
involves a possible threat, because there is always a moment where
you have noticed that something unexpected has just happened, but
you haven't yet figured out what it is. Since many surprises are
in fact threats, such as a leopard springing into view, you
can't afford to wait until you've figured out the nature of the
surprise, and then to respond quickly only if needed.
Instead, it's important to prepare for a fight or flight
response as soon as you are surprised, just in case the surprise turns
out to be a threat. If you then see that there is no threat, it will
still trigger the laughter response that results
whenever a possible threat has suddenly gone away.
In a typical joke, for example, there is a punchline that
suddenly makes it clear that various assumptions that you've made
about the story are completely wrong, and that the story elements
actually fit together in a completely different way. This is
initially surprising and perhaps disturbing, but once it registers
that the surprise was simply due to "getting" a harmless joke, then the
possibility of a threat from the surprise has suddenly gone away,
Another type of humorous surprise is a deadpan statement that doesn't really
reflect your beliefs. There is a brief moment when the listener notices
that the comment is surprising, before they realize that you are
being sarcastic, quickly triggering relief.
How Humor Removes a Possible Threat in Other Ways
Humor can remove potential threats in ways other than by setting up
surprises that turn out to be non-threatening. For example,
much humor involves admitting something stupid that you've done, or
some embarrassing trait that you have. Often this is something that's
true for most listeners as well, and they have worried about what might
happen if they admitted it. When you come out and admit it about
yourself, and nothing terrible results from that,
it makes it clear to listeners that they have
overestimated the negative consequences of admitting it about
themselves, and the relief triggers laughter.
Such self-deprecating humor is especially effective when done
by people who are seen as very successful. If even a successful
person has a particular foible, then it's not much of an
embarrassment for you to have it too.
A similar way that humor can burst a perceived threat
is by exposing bullshit. You may be harboring a complaint
about the same bullshit, but you haven't expressed the complaint
for fear of aggression by those who disagree, or of
being seen as someone who holds unusual (and therefore likely
inappropriate) views. When someone else comes right out
with the same complaint, perhaps even exagerating it with
hyperbole for humorous effect, it demonstrates that doing so is
acceptable (or at least that it can be gotten away with).
And when a whole audience laughs, it becomes clear that your
view that the comedian dared to express is not at all unusual.
"Potty humor" may be the most basic example of this type of
humor, by defying the bullshit rule against joking about such
"degrading" things, even though bodily functions are a basic and
important part of life.
Even a joke that has a surprise ending can quickly remove a
possible threat in a non-surprise way as well. When we find
ourselves in a situation that we can't make much sense out of,
that's scary because we can't even figure out if there is a
threat or how we should respond to it if there is one. A joke-teller
can create such a situation by setting up a world that doesn't
seem to fit together. Getting the joke suddenly makes
everything make sense, and the relief of that adds to the usual
relief of realizing that the surprise ending is not a new threat.
Getting a joke may also suddenly remove a fear that we weren't
going to get the joke, and appear stupid!
Ridiculing an Enemy Makes Them Less of a Threat
If you make a humorous remark that demonstrates that the enemy is
rather incompetent, then the enemy suddenly appears to be a less
formidable threat, and the relief results in laughter. And if the
joke is perceived as being particularly clever, then the foe
may seem like even less of a threat because they are surely no
match for us clever folk who all got the clever joke. A
quick realization that the foe is not much of thread results
But Laughter for Intimidation Is Not True Laughter
Humor that ridicules an enemy that is not present should not be
confused with laughing "at" someone who is present,
to intimidate them. The latter is intentional (fake)
laughter, and not true involuntary laughter at all.
The intimidation effect works because we understand that the
object of laughter is regarded as a non-threat. So this sort
of forced laughter for intimidation is a secondary phenomenon
that developed only after we had a partial understanding of
Slapstick could be regarded as laughing "at" others in a natural way.
But the laughter results only when the initial shock of seeing
someone harmed is quickly followed by the conscious realization
that they're not really being harmed. Seeing a foe do something
stupid could spark true laughter from seeing that they are not
a threat, or forced laughter to ridicule them, but not true
laughter to ridicule them.
A Note About Tickling
Tickling is a source of laughter that also occurs in other
species, and therefore may be the original source of laughter.
The main response to tickling is to try to remove the source of
the tickle. This reaction probably was selected for because
it can quickly remove insects and other parasites before they
manage to bite us, when we notice the tickle sensation of them
crawling on our skin. We are therefore especially
ticklish on the bottoms of our feet, for example, where we are
especially likely to make contact with other creatures by stepping
on them. We are also very ticklish
under our arms, where parasites are likely to take
refuge in that warm moist area.
But if we see that the source
of the tickle is not a possibly harmful creature, and is instead
another human who's having some fun with us, only then does the
tickling result in laughter. Perhaps a mother is compelled to
tickle her infant because that gives the infant practice at
accurately swatting parasites. The infant laughs because it then
relaxes and further bonds with its mother who is providing the
Subverting the Drudgery of Life that Has Evolved Only to Reproduce Genes
Natural selection leads us to work constantly to maximize our
reproductive rate, rewarding us with pleasure only for putting
in the work. Humor subverts that dicate by exploiting pleasure
responses that evolved for other reasons, providing pleasure
for free. An oasis of pure joy amidst the daily grind of life.
[ The narrative above includes some ideas that have been widely
expressed by others, plus many ideas of my own to fill in the holes
and for clarification. In particular, there seems to be a dearth of
explanations about why the particular physiological response
of laughter is involved in humor, as opposed to some other response
like jumping up and down while holding our breath, so I tried to
address that question. ]
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