How does evolution explain...

[Woodbutcher]

Walking around my post route this morning something prompted me to start thinking about being tickled. When I'm left with nothing but my own thoughts for company several hours a day at work I can quite often over think certain minor things and today was no exception. After thinking about how odd the sensation of being tickled is, I started to contemplate why we've evolved with this trait in the first place.

Darwin's theory of evolution tells us that natural selection favours traits that give their organism an advantage over others of it's kind or predators it may encounter. Sure, there are cases where a certain trait appears illogical and even decreases the chances of survival for a species but most of them (like the disposition of female Peacocks to select males with more impressive tail feathers) can be linked in to sexual selection and is explained as a way for animals to strive for "better" genes passed to their offspring.

The sensation of being tickled doesn't conform to either natural or sexual selection. In fact, it's a disability and possible danger for an animal to have a tickle reflex since when you get going it positively immobilises you on the spot and prevents you from fighting or fleeing which would suggest that animals without this reflex would have an advantage, however slight, over one that does have it. Obviously when a lioness is bounding after you it's not to have a quick tickle at your ribs but it would still be a disadvantage in some scenarios I'm sure.

We also don't select a mate dependant on whether or not they appreciate a good tickle and there's no way of telling if a person is ticklish just by looking at them so it clearly has nothing to do with sexual selection.

For me, this falls under the same kind of heading as why we appreciate music, in Daniel C. Dennett's book Breaking the Spell he suggests that we have evolved to lose ourselves in certain beats, rhythms and melodies as a way of coping with and easing stress and he argues that in our more primitive past religion possibly had the same effect and so it was of evolutionary benefit to us. Just like our appreciation of music (tried really hard to find a decent video of a parrot that's clearly moving to a beat but failed ), it's also not something that is exclusive to humanity



Could tickling have had the same benefit in our past or is it possibly something that we have developed more recently in our history with the onset of society and the relative saftey it provides us as a species meaning things that would have set us back, like being immobilised by touching certain parts of out skin, have more of a chance to develope since they don't pose enough of a threat to significantly decrease our chances of survival?

If the sensation only manifested itself when you get your feet tickled then I could understand this trait a bit more since looking at the way our brain works shows that the parts that deal with sensory perception of your feet are right beside those that register the perception of your genitals (represented by a Sensory Homunculus below) and so some sort of neural cross firing or synethsesia could be the cause of it. When you think about it, the feeling you get while being tickled isn't too dissimilar to the feeling you get when you orgasm all be it on a much smaller scale which is probably what made me think of the connection between sensory regions in the brain in the first place (coupled with the fact that feet are often the most suseptable to being tickled)



Wikipedia clases being tickled in two different ways:

knismesis (light tickling)

Knismesis refers to the light, feather-like type of tickling. This type of tickling generally does not induce laughter and is often accompanied by an itching sensation.[2] The knismesis phenomenon requires low levels of stimulation to sensitive parts of the body, and can be triggered by a light touch or by a light electrical current. Knismesis can also be triggered by crawling insects or parasites, prompting scratching or rubbing at the ticklish spot, thereby removing the pest. It is possible that this function explains why knismesis produces a similar response in many different kinds of animals.[2] In a famous example, described in Peter Benchley's Shark!, it is possible to tickle the area just under the snout of a great white shark, putting it into a near-hypnotic trance.[3]

and gargalesis (heavy tickling)

Gargalesis refers to harder, laughter-inducing tickling, and involves the repeated application of high pressure to sensitive areas.[2] This "heavy tickle" is often associated with play and laughter. The gargalesis type of tickle works on humans and primates, and possibly on other species.[4] Because the nerves involved in transmitting "light" touch and itch differ from those nerves that transmit "heavy" touch, pressure and vibration, it is possible that the difference in sensations produced by the two types of tickle are due to the relative proportion of itch sensation versus touch sensation.[5]

While it is possible to trigger a knismesis response in oneself, it is usually impossible to produce gargalesthesia, the gargalesis tickle response, in oneself.[2]

Hypergargalesthesia is the condition of extreme sensitivity to tickling. [6]

From those articles there's another possible evolutionary advantage to being lightly tickled, I.e, in order to tell that something possibly dangerous is maybe crawling on your skin, the itchy feeling that accompanies it could be a reflex action designed purely to get whatever is on you away from your body since your hand will brush the spot that itches instinctively.

Reading more from Wikipedia there is actually a bit about what Darwin apparently thought about the reaction:

Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure.[9] If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, and reasoned that this is why you cannot effectively tickle yourself.

A good point but I don't think it answers the effect as fully as it should,

If you want to read the full article then the link is HERE

This seems to explain why my mail is always fucking late.....

[Pappa]

This is what can be found about the evolution of tickling on some other sites:

I recently read about an experiment to discover if tickling and laughter were inherently linked in humans or whether the response was culturally learned. The experimenter used his own children as the subjects, tickling them, without any laughing or smiling (or even the ability to see his face. In both cases, they children spontaneously began laughing when they were tickled at 7 months old.

http://www.spring.org.uk/2007/11/are-we ... ickled.php

[The Curious Squid]

Thanks Ryokan

It is an interesting subject, are there any other examples of animals laughing or even tickling each other besides rats and primates? I'd be interested to find out if this trait is apparant in Dolphins since they are supposed to be quite intelligent. Does water get in the way of the reflex reaction to tickling?

[FedUpWithFaith]

Neat thread Paco.

I've never heard anyone argue about the evolutionary genesis of tickling before which surprises me given my neurophysiology background. If it's true that rats and many other animals have a tickle reflex, I find it doubtful, though not impossible, that this is a case of collateral evolution without purpose, as some argued. On the other hand, I really wonder how many animals really have a tickling reflex. I have had many dogs, highly intelligent and social animals of course, and I've tried tickling many but none tickles like a human. Yeah, you can find just the right spot to make them twitch their leg, but they don't seem to do anything akin to laughing when you do it (I can get a laugh-like response from my dogs for other stimuli though). If anything, they merely tolerate it and It seems to annoy them. As for cats, even if they don't bite you when they get "tickled" it's not clear to me that they are responding to the same or similar sensation we get from tickling.

However, if tickling is a prevalent in the mammalian genus as suggested by the rat experiment, then I find Darwin's explanation wanting as well. Perhaps Darwin has a point pertaining to why the tickling reflex has persisted in humans and perhaps some higher-order social animals but it doesn't seem a very convincing explanation for how it arose in the first place if it is really very prevalent.

My guess is that tickling-reflexes are one of those traits that arose for one clear, really useful purpose and then migrated, adapted, and perhaps diluted to other, maybe lesser purposes that might persist with the help of some collateral linked evolution. If I'm right, this begs the question of where the tickling reflex first arose (or multiply arose among various species) and why. So we need to do a lot more research into the origin of tickling. Unfortunately, I'd guess is that a paper entitled "A Putative Tickling Response in Red Worms (Lumbricus Rubellus)" would draw the ire of grandstanding Congressman about wasteful spending.

[lordpasternack]

What I find interesting is that often when you ask someone what sexual arousal feels like - they describe it as being like a "tickle" - and some describe sexual frustration as being an "itch". But it isn't tickly - because you don't want to (literally) scratch it...

Anyone?

[charlou]

Just like our appreciation of music (tried really hard to find a decent video of a parrot that's clearly moving to a beat but failed ), it's also not something that is exclusive to humanity

Here you go, Paco:

[youtube]http://www.youtube.com/watch?v=WspxV2SX ... re=related[/youtube]


In Australia pet galahs are often easily trained to repeat (parrot) phrases such as the popular "dance cocky" (the key words I used to search youtube) while 'dancing', and they seem to get quite immersed in it. They're making their own music.

[Beelzebub2]

It is an interesting subject, are there any other examples of animals laughing or even tickling each other besides rats and primates? I'd be interested to find out if this trait is apparant in Dolphins since they are supposed to be quite intelligent. Does water get in the way of the reflex reaction to tickling?

Some studies suggest that members of the order Cetacea (dolphins, porpoises, and whales) may be laughing too. As far as dolphins are concerned, intelligence studies have shown that two dolphins can refer to a third dolphin by name. Given the range of vocal performance by dolphins and whales, it would not be surprising to find out these animals laugh as well.

What puzzles scientists is what the animals are laughing about. Some studies suggest animals laugh when they are excited or happy. Others believe animals laugh to gain the attention of their owners. It is possible animals laugh when they are enjoying play. It is possible that animals laugh because it confers health benefits to them, just as laughing is very good for people. Laughter can lower blood pressure, ease stress, produce dopamine and growth hormone, and actually be good for the circulatory system. Preschool children may laugh as often as 400 times a day. Since some animals have about the same intelligence level as a two year old human, there is a possibility that these animals laugh for the evolutionary benefits achieved by laughing. A chimp that laughs, for example, may be a bigger chimp because he stimulates growth hormones.
Do animals laugh?

But apparently no one made any studies about ticklishness of dolphins.


There is one nice nice article about evolution of human laughter from the PubMed:

The evolution and functions of laughter and humor: a synthetic approach
A number of recent hypotheses have attempted to explain the ultimate evolutionary origins of laughter and humor. However, most of these have lacked breadth in their evolutionary frameworks while neglecting the empirical existence of two distinct types of laughter—Duchenne and non‐Duchenne—and the implications of this distinction for the evolution of laughter as a signal. Most of these hypotheses have also been proposed in relative isolation of each other and remain disjointed from the relevant empirical literature. Here we attempt to remedy these shortcomings through a synthesis of previous laughter and humor research followed by a reevaluation of this research in light of theory and data from several relevant disciplines, and the proposal of a synthetic evolutionary framework that takes into account phylogeny and history as well as proximate mechanisms and adaptive significance. We consider laughter to have been a preadaptation that was gradually elaborated and co‐opted through both biological and cultural evolution. We hypothesize that Duchenne laughter became fully ritualized in early hominids between four and two mya as a medium for playful emotional contagion. This mechanism would have coupled the emotions of small hominid groups and promoted resource‐building social play during the fleeting periods of safety and satiation that characterized early bipedal life. We further postulate that a generalized class of nonserious social incongruity would have been a reliable indicator of such safe times and thereby came to be a potent distal elicitor of laughter and playful emotion. This class of stimuli had its origins in primate social play and was the foundation for formal human humor. Within this framework, Duchenne laughter and protohumor were well established in the hominid biobehavioral repertoire when more cognitively sophisticated traits evolved in the hominid line between two mya and the present. The prior existence of laughter and humor allowed them to be co‐opted for numerous novel functions, and it is from this process that non‐Duchenne laughter and the “dark side” of laughter emerged. This perspective organizes the diversified forms and functions that characterize laughter and humor today and clarifies when and how laughter and humor evolved during the course of human evolution.

And another:

Human laughter, social play, and play vocalizations of non-human primates: an evolutionary approach
It has been hypothesized that the evolutionary origin of human laughter lies in the facial play signals of non-human primates. Recent studies dealing with human laughter have stressed the importance of the acoustic component of this nonverbal behaviour. In this study, we analysed the occurrence and some acoustic parameters, such as interval durations and fundamental frequency, of Barbary macaque and chimpanzee play vocalizations and human laughter during tickling. Play vocalizations occurred most often during play with close bodily contact, i.e. wrestling and tickling. In both Barbary macaques and chimpanzees, they were serially organized and had a high intra-bout variability in their acoustic parameters. These are characteristic features of human laughter which are crucial for deciding whether a given utterance will be classified as laughter in humans. Besides intra-bout variability, there was substantial intraindividual variability which was as high or higher than the interindividual variability in all three species. Interval durations of Barbary macaque and chimpanzee play vocalizations and human laughter during tickling lay in a similar range. These results provide further evidence for the hypothesis that human laughter evolved from a play signal of non-human primates and raise questions about the importance of and the relationship between facial and vocal play signals in the evolution of human laughter.

Some other links here and here.