Laughter in animals other than human beings describes animal behaviour that resembles human laughter.
Several non-human animals have vocalisations that sound similar to human laughter. A large proportion of these animals are primates, which indicate that neural functions evolved early in the mammalian development process.
Chimpanzees, gorillas, bonobos and orangutans show laughter-like vocalisations in response to physical contacts, such as wrestling, playing or tickling. This behaviour is documented in both wild and captive chimpanzees. Chimpanzee laughter is not readily identifiable to humans as such, because it is caused by simultaneous inhalations and exhalations that sound more like breathing and panting.
This sounds like screeching. Differences between chimpanzees and human laughter can be the result of adaptations that have developed to make human speech possible. One study analysed the sounds of human babies and bonobos when tickled. It was found that while Bonobo’s laughter was higher, the laughter followed the same sonographic pattern of human infants to include similar facial expressions. Humans and chimpanzees share similar ticklish areas of the body, such as the armpits and the stomach.
Research has shown similarity in styles of laughter between humans and apes (chimpanzees, bonobos, gorillas, orangutans) when tickled, indicating that laughter originated from a shared origin among primate species and thus developed prior to human origin.
Rats emit long, 50-kHz ultrasonic calls that are triggered during rough and turbulent play and when tickled by humans. Vocalisation is represented as a separate “chirping.” Like humans, rats have “tickle skin,” parts of the body that produce more laughter than others. The rats who laugh the most play the most, and tend to spend more time with the other rats who laugh.
It has been noted that there is no decrease in the tendency to laugh and respond to tickle skin as rats mature, but it has also been reported that in females, brain maturation after puberty appears to reinterpret tickling as aversive, leading to averting rather than an appetising response. Further studies show that rats chirp when wrestling with each other, before receiving morphine, or when reproducing. The sound was interpreted as an anticipation of something rewarding. High-frequency ultrasonic vocalisations are critical for rat communication and work in the recipient’s approach actions.
The initial goal of Jaak Panksepp and Jeff Burgdorf ‘s work was to trace the biological basis of how the brain regulates emotions and social actions. Researchers associated rat vocalisations during social interactions with the excitement and laughter usually felt by children in social play. They concluded that 50-kHz rat vocalisations that represent positive affective states (feelings or emotions) similar to those experienced by children laughing during social play.
More recent studies have examined the emotional state of rats after they have been tickled. The optimism or pessimism of the animal can be assessed through cognitive bias studies. After being tickled, rats are more optimistic, indicating that the interaction invokes a positive affective state. In addition, rats self-administer 50-kHz trill call playback and avoid 22-kHz call playback.
If naloxone (an opioid antagonist) is administered to rats, tickling no longer evokes 50-kHz vocalisation, which means that the rewarding properties of tickling are modulated by endogenous opioids.
Dogs often pant in a way that sounds like a human laugh. By analysing the pant using a sonogram, this pant varies with frequency bursts. If this vocalisation is performed on dogs in shelter environments, it can encourage play, facilitate pro-social behaviour and lower stress rates. One research contrasted the behaviour of 120 dogs with and without exposure to a reported “dog-laugh.” Playback decreased stress-related behaviour, increased tail wagging, “play-face” display while playing, and pro-social behaviour such as approaching and licking the lips.
In 2004, researchers researching dolphins in Sweden detected a specific series of sounds that they had not heard before. Such sounds consisted of a brief burst of pulses accompanied by a whistle. After further studies, the researchers found that such signs were produced only by dolphins during play-fighting, and never during hostile confrontations. Their hypothesis was that these noises were created by the dolphins to show that the situation was friendly and/or unthreatening, and to help prevent it from escalating into anything like a real battle. This, according to psychologists, is the reason why there is laughter in the first place, implying that such sounds were the dolphin counterpart to human laughter.
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