In a previous post, AnimalWise saluted the red-footed tortoise (Geochelone carbonaria) for its Ig Nobel Prize achievements but, in doing so, may have unfairly maligned the tortoise’s cognitive capabilities. To atone for any past disparagement, this post is dedicated to an impressive, and perhaps surprising, red-footed tortoise intellectual accomplishment.
Many social animals are able to solve problems and shortcut the costly process of trial and error learning by simply observing the behavior of their peers. While some have speculated that this type of observational learning is an adaptation for social living that may be unique to animals who live together in groups, a research team led by Anna Wilkinson of the University of Vienna wanted to see whether a decidedly non-social animal, the red-footed tortoise, could also learn by observing others. Wilkinson specifically hoped to test the hypothesis that social learning abilities may simply be a reflection of an animal’s general learning capacity, and that non-social animals may be able to learn by observing peer behavior in fundamentally the same way as they use other environmental stimuli to learn.
Finally – respect for my brains as well as my dashing good looks!
The red-footed tortoises were perfect subjects for this study. The natives of Central and South American forests are naturally solitary, receiving no parental care (once the eggs hatch, it’s every little tortoise for himself and herself!) and, unless presented with a mating opportunity, living apart from other tortoises.
For Wilkinson’s study, eight young (juvenile or sub-adult) tortoises – four randomly assigned to the “non-observer” condition and the other four assigned to the “observer” condition – participated in a series of trials in which they needed to navigate around an obstacle to achieve a food reward. All trials took place in a square arena in which a 40 cm high V-shaped fence separated the tortoise from the desired food:
First, the tortoises in the non-observer groups were each given 12 trials (one per day) in which they were allowed two minutes to solve the task. Between trials, the bark flooring in the arena was redistributed to prevent the tortoises from being able to latch onto any scent trails from prior trials.
Next, the observer group tortoises had their turn. Their trials were identical except that, before each test, they were able to observe a specially-trained tortoise who invariably detoured around the right side of the obstacle and ate the food prize.
The results were unambiguous. While none of the non-observer tortoises ever solved the puzzle (they went up to the fence by the food, but never figured out how to go around the obstacle), all of the observer tortoises succeeded at least twice, with two of them correctly navigating around the barrier on the first attempt.
In other words, the red-footed tortoises have another addition for their trophy room. Not only are they the first red-footed and hard-shelled recipients of the Ig Nobel Prize, they are also the first non-social reptile to display social learning skills, revealing that group living is not necessarily a prerequisite for social learning.
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Wilkinson, A., Kuenstner, K., Mueller, J., & Huber, L. (2010). Social learning in a non-social reptile (Geochelone carbonaria) Biology Letters, 6 (5), 614-616 DOI: 10.1098/rsbl.2010.0092.
Last week, British parents who had hidden their child’s gender from the world finally revealed that their five year old, now ready to enter school, is a boy. While the parents had hoped to raise their son Sasha in a gender-neutral way (“Stereotypes seem fundamentally stupid. Why would you want to slot people into boxes?”), their approach raised eyebrows and controversy. Were they creating an environment where their child could find his own gender identity, free from crippling societal expectations, or were they conducting a bizarre and possibly harmful experiment on a family member?
Putting aside the issue of whether the parents acted appropriately, the story raises fascinating questions about gender-specific traits and preferences. To what degree are gender differences innate and biological, and to what extent do they arise out of societal modeling and environment?
Some (including Sasha’s parents) may see gender preferences as being primarily influenced by human social pressures, but there are indications of biological influences as well. For example, girls with a particular genetic condition that exposes them to high prenatal levels of androgen often show “masculine” toy preferences, even when their parents strongly encourage them to play with female-typical toys. Given the intertwining impacts of nature and nurture in human societies, can we learn anything from our animal relatives who grow up free from human societal norms?
In this post, I’d like to take a look at two recent studies that examine differing male and female toy preferences in primates.
Male Monkeys Prefer Trucks
First, in 2009 a research team led by Janice Hassett of the Yerkes National Primate Center at Emory University reported on experiments in which they the researchers to see whether rhesus monkeys (Macaca mulatta) would exhibit gender-specific toy preferences similar to those of human children.
In humans, studies have shown that boys gravitate strongly to stereotypically “masculine” toys such as trucks and other vehicles, while girls are less rigid, spending relatively equal amounts of time playing with boy-favored toys and with more traditionally “feminine” toys such as dolls. One hypothesis put forward to explain this difference has been that boys face greater societal discouragement when they play with “girl toys” than girls do in the reverse situation. The researchers figured that by looking at rhesus monkeys, who don’t face comparable social pressures to conform to gender roles, they might be able to illuminate biological influences on toy selection as well.
Of course I'm not playing; you gave me a Raggedy-Ann. Pass me that truck. Now. (photo credit: J.M.Garg, Wikipedia)
In their study, the researchers compared how 34 rhesus monkeys living in a single troop interacted with human toys categorized as either masculine or feminine. The “masculine” set consisted of wheeled toys preferred by human boys (e.g., a wagon, a truck, a car, and a construction vehicle); the “feminine” set was comprised of plush toys comparable to stuffed animals and dolls (e.g., a Raggedy-Ann™ doll, a koala bear hand puppet, an armadillo, a teddy bear, and a turtle). Individual monkeys were released into an outdoor area containing one wheeled toy and one plush toy, with the researchers taping all interactions using separate cameras for each toy, identifying all specific behaviors, and statistically analyzing the results.
The results closely paralleled those found in human children. As with human boys, male rhesus monkeys clearly preferred wheeled toys over plush toys, interacting significantly more frequently and for long durations with the wheeled toys. Also mirroring human behavior, female rhesus monkeys were less specialized, playing with both plush and wheeled toys and not exhibiting significant preferences for one type over the other. Here’s a chart illustrating the similar gender preferences of humans and rhesus monkeys (the information regarding human preferences comes from a 1992 study by Sheri Berenbaum and Melissa Hines):
The researchers noted that these similarities show that distinct male and female toy preferences can arise in the absence of socialization pressures and hypothesized that “there are hormonally organized preferences for specific activities that shape preference for toys that facilitate these activities.”
Barbie Really Is a Stick Figure
Next, in a brief paper published in 2010, Sonya Kahlenberg of Bates College and Richard Wrangham of Harvard University presented the first evidence of wild male and female primates, chimpanzees (Pan troglodytes) in the Kanyawara chimpanzee community of Kibale National Park, Uganda, interacting differently with play objects.
Over a 14 year period, Kahlenberg and Wrangham observed that juvenile Kanyawara chimpanzees tended to carry sticks in a manner suggestive of rudimentary doll play and that the behavior was more common in females than in males. Juvenile chimps, particularly females, would carry around small sticks for hours at time while they engaged in other daily activities such as eating, climbing, sleeping, resting and walking. While the same chimps used sticks as tools for specific purposes, the researchers were unable to discern any practical reason for the stick-carrying. The following chart shows the degree to which female chimps were more likely to engage the in stick carrying behavior:
Age and sex differences in the rate of stick-carrying in chimpanzees. Females: circles, solid line. Males: triangles, dashed line.
The researchers hypothesized that “sex differences in stick-carrying are related to a greater female interest in infant care, with stick-carrying being a form of play-mothering (i.e. carrying sticks like mother chimpanzees carrying infants).” In support of this proposition, they pointed to several factors. First, they never observed stick carrying by any female who had already given birth; that is, stick-carrying ceased with motherhood. Also, the chimps regularly carried sticks into day nests where they “were sometimes seen to play casually with the stick in a manner that evoked maternal play.” Finally, nurturing behavior towards objects like sticks had previously been reported in captive chimps and documented on a couple of occasions in the wild.
Also, the researchers suggested a social rather than biological basis for the behavior. Because regular stick-carrying hasn’t been reported in other wild chimpanzee communities, they proposed that that young Kanyawara chimpanzees may be learning the behavior from each other as a way of practicing for adult roles – a form of social tradition passed between juveniles previously described only in humans. Kahlenberg and Wrangham conclude by noting that:
Our findings suggest that a similar sex difference could have occurred in the human and pre-human lineage at least since our common ancestry with chimpanzees, well before direct socialization became an important influence.
So there you have it. One rhesus monkey study positing a biological and hormonal basis for gender-specific play, and another chimpanzee study emphasizing social learning… At least for now, the threads of nature and nurture impacting gender roles seem difficult to disentangle for non-humans, just as they are for us.
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Hassett, J., Siebert, E., & Wallen, K. (2008). Sex differences in rhesus monkey toy preferences parallel those of children Hormones and Behavior, 54 (3), 359-364 DOI: 10.1016/j.yhbeh.2008.03.008.
Berenbaum, S., & Hines, M. (1992). EARLY ANDROGENS ARE RELATED TO CHILDHOOD SEX-TYPED TOY PREFERENCES Psychological Science, 3 (3), 203-206 DOI: 10.1111/j.1467-9280.1992.tb00028.x.
Kahlenberg, S., & Wrangham, R. (2010). Sex differences in chimpanzees’ use of sticks as play objects resemble those of children Current Biology, 20 (24) DOI: 10.1016/j.cub.2010.11.024.
Apparently, parrots aren’t just smart, they’re competitive too. A couple of months ago, we covered recent research findings on contagious yawning in animals, reporting on the rarity of the phenomenon and its potential role as a form of social mimicry or even an indication of empathy. While certain primates clearly do yawn contagiously and dogs may yawn contagiously, the behavior hadn’t been reported in other animals and had been expressly ruled out in red-footed tortoises (although the tortoises may have had the last laugh, as they won the celebrated Ig Nobel Prize for their non-yawns).
Word of our mammal-centric coverage seems to have reached the small, oval ears of the always-influential parrot lobby, though, as just last week the journal Behavioural Processes published a study describing social yawning in budgerigars (Melopsittacus undulatus), the small Australian parrot often referred to as the parakeet. This study provides the first support for contagious yawning in a non-mammal, and even ups the ante by documenting what may be the first instance of contagious stretching, another stereotyped behavior that may play a social role for certain animals. Some may say that the paper’s timing is an utter coincidence and that only someone with delusions of grandeur would believe that it was even remotely linked to the AnimalWise post. We, speaking in our usual royal manner, prefer to think otherwise.
Fascinating, simply fascinating...
Michael Miller, Andrew Gallup and other researchers from the University of the Binghamton conducted an observational study of yawning and stretching in a group of approximately 20 adult male and female budgerigars living together in an aviary as an established flock. Over a period of about a year and a half, the research team video recorded the flock on 23 separate occasions. The recording sessions, each of which lasted 90 minutes, were conducted at varying times of the day, and the researchers took a number of precautions (such as ignoring the first 15 minutes of each tape) to ensure that the flock’s behavior was as natural and undisturbed as possible. Trained reviewers then systematically reviewed all of the tapes, recording the time and occurrence of each yawn and stretch, and categorizing each stretch by whether the bird extended one or both legs.
The researchers’ hypothesis was that, if yawning and stretching were spreading contagiously among the birds, the behaviors would occur in nonrandom “clumps” – that is, rather than being evenly dispersed throughout the recording sessions, multiple yawns (or multiple stretches of the same type) would take place in closely-spaced bouts and then be followed by a long interval until a new priming behavior triggered another bout. Further, they predicted that, although there might be might be overall tendencies tied to particular times of the day (for example, the budgerigars might, on average, yawn more frequently during evening sessions), if the yawning and stretching really were being triggered contagiously, then specific clumping patterns would not repeat themselves when multiple same-time-of-day sessions were compared.
To test their hypotheses, the researchers performed detailed, session-by-session analyses of each type of behavior. For example, they tallied how frequently each behavior occurred, measured the time between adjacent stretches and yawns, and sorted the adjacent pairs into different “bins” depending on the length of the interval. They also analyzed each session for clumping by breaking it down into a large number of short (20 to 30 second) intervals, which allowed them to identify “runs” of consecutive intervals that either did, or did not, contain the behavior in question. Finally, they statistically analyzed their data in a variety of ways to identify patterns and associations.
And the results?
Both yawning and stretching behaviors were indeed clustered within trials, and the period between adjacent yawns and stretches was “strongly biased toward very short (< 20 sec) and very long (> 300 sec) intervals,” especially for the yawns. Also, as hypothesized, despite the clustering for both behaviors, “neither behavior routinely occurred at specific times from the start of a session across multiple recordings at the same time of day. This suggests that the clumping of these behaviors was due to social influences, and not to underlying physiological effects as a result of similar circadian patterns.”
The research team summarized its findings and suggested directions for future investigation as follows:
The observational results presented here suggest that yawning and stretching are at least mildly contagious in budgerigars under semi-natural flock-living conditions. In line with each behavior’s presumed physiological function, contagious yawning and stretching may ultimately coordinate mental state and a group’s collective movements, but future research needs to test these predictions.
So, kudos to the budgerigars! Parrots everywhere can take pride in these findings, which point to previously-unknown areas of avian social signaling and coordination, and which may open up new avenues for studying collective behavior.
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Miller, M., Gallup, A., Vogel, A., Vicario, S., & Clark, A. (2011). Evidence for contagious behaviors in budgerigars (Melopsittacus undulatus): An observational study of yawning and stretching Behavioural Processes DOI: 10.1016/j.beproc.2011.12.012.
In the middle of the 1980s, a catastrophic event shattered the lives of a troop of olive baboons (Papio anubis) living in the Masai Mara Reserve in Kenya. While the troop ultimately survived the experience, it emerged as a fundamentally transformed society with new cultural traditions. This is its story.
The troop, known as the Forest Troop, was initially very much like other olive baboon troops – that is to say, an extremely hierarchical and aggressive society, fraught with battles for dominance and bullying of subordinates. While a female will remain with her birth troop for life and automatically inherit her mother’s social ranking, a male reaching adolescence must set off on his own to find a new troop and then jockey with other males for position on the social ladder. The stakes are high, as baboon society is polygamous and dominant males enjoy the best access to mating and food resources.
And so it was. The Forest Troop lived in the woods and slept in trees about a kilometer from the open-air garbage pit of a nearby tourist lodge. Over time, many of its most aggressive males got into the habit of traveling to the garbage pit at dawn in order to scavenge for food, fighting for scraps with the males of a neighboring troop.
Then, in 1983, disaster struck. Spoiled meat that had been discarded in the garbage pit caused a fatal epidemic of bovine tuberculosis. Every single Forest Troop male who had foraged for food at the pit – 46% of the troop’s adult males – died in the outbreak. The remainder of the devastated troop, comprised solely of females and less aggressive males, survived.
In the wake of the outbreak, researchers who had been observing the Forest Troop noticed a dramatic reduction in certain types of aggressive behavior within the troop, not a particularly surprising observation given the loss of all of the most aggressive males in the troop. However, because the researchers wanted to focus on an intact troop that hadn’t experienced social disruption, they turned their attention away from the Forest Troop and shifted their efforts to studying a nearby troop that hadn’t been impacted by the outbreak.
A number of years later, though, the researchers returned to the Forest Troop and noticed something fascinating – even though there had been a complete changeover in the troop’s adult males, the troop’s less aggressive behavioral features had persisted. That is, a new generation of baboons in the Forest Troop appeared to be carrying on what amounted to a cultural tradition of lessened baboon aggression.
Geez, another housewarming party?! That Forest Troop has GOT to be some sort of a cult or something. (photo: Philippe_Boissel)
In order to analyze the changed behavior more rigorously, the researchers engaged in what’s known as a “focal sampling” process. They systematically recorded the social behavior of individual Forest Troop baboons from 1993 through 1996, and then compared those observations to two other data sets that served as controls – pre-outbreak observations they had made of the Forest Troop from 1979 to 1982, and mid-1990s observations of a different olive baboon troop.
What they found bore out their initial impressions. In particular, the new generation of Forest Troop baboons displayed patterns of dominance and aggression behavior that created less stress for low-ranking males. While the overall number of incidents involving aggression and dominance behavior was comparable to that seen in the control cases, the mix was different. Forest Troop confrontations were now significantly more likely to involve closely-ranked males, as opposed to the control group behavior pattern in which very high ranking males tended to pick on the lowest-ranking ones. This is notable, as confrontations between baboons with large power disparities typically reflect harassment rather than true competition and can be particularly stressful to the lower-ranking subordinates. Moreover, in the post-epidemic Forest Troop, males acted less aggressively towards females, engaged in more social grooming with females, sat in closer proximity to other baboons, and were more likely to have adult females, infants, adolescents, and juveniles as neighbors. Finally, the researchers found that subordinate baboons in the kinder and gentler Forest Troop had much lower levels of glucocorticoids, adrenal hormones secreted in response to stress, than did subordinates in the control groups.
C’mon, Dad, faster! Bumbo and Uncle Phil are waaaay ahead of us!
The researchers next considered how the peaceful new social traditions of the Forest Troop were being passed on to new males joining the troop: were troop members teaching the newcomers to be less aggressive, were new arrivals learning through observation or because they had more opportunities for friendly interactions, or was self-selection causing less aggressive males to gravitate toward this more peaceful troop? The researchers found that new males acted with typical aggression upon arriving at Forest Troop and were greeted with the usual belligerence from other males, but that the Forest Troop females were now uncharacteristically welcoming to the new arrivals, grooming them and otherwise treating them as established residents. Because the females didn’t seem to be engaged in active teaching behavior (they showed the same friendly behavior to even the most aggressive of the newcomers), the researchers concluded that the peaceful Forest Troop cultural traditions were most likely being passed on as newcomers observed more positive interactions with females and had more opportunities to relate non-aggressively themselves.
So, out of ashes of death, a baboon troop forged a new culture and found a way to maintain its peaceful traditions, passing them along to new generations. Makes one think….
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Sapolsky, R., & Share, L. (2004). A Pacific Culture among Wild Baboons: Its Emergence and Transmission PLoS Biology, 2 (4) DOI: 10.1371/journal.pbio.0020106.
If you’re a female elephant, there’s a right way and a wrong way to play the mating game. To maximize your chances of reproductive success, it’s best to pair up with a dominant bull elephant in musth, a state of heightened arousal in which testosterone courses through the bull’s body, increasing both his sex drive and his aggression. A high-ranking musth elephant not only makes the fittest mate, but he can protect you by scaring off the less desirable younger males who would otherwise chase you around.
An experienced female knows this well, and plays the game accordingly. When she goes into heat – or oestrus – and attracts male suitors through chemicals in her urine, she gives impressive senior bulls the green light by holding her tail high, walking with an exaggerated gait, and exchanging affectionate trunk caresses. Lower-ranking young males don’t fare so well. She actively avoids them and, to the extent they aren’t chased off by her favored partner, she’ll often spurn their advances by running away. (Little known fact: female African elephants can typically outrun male ones.)
It’s not so easy for a young female entering oestrus for the first time. She sometimes runs from the larger musth males, who can weigh more than twice as much as her, and not infrequently ends up consorting with a series of younger, lesser males. This can lead to unfortunate results, especially when you consider that an elephant pregnancy lasts 22 months.
Now, though, there’s evidence that experienced females may help their younger relatives in sorting through the confusing tangle of elephant sexual dynamics. These helpful older elephants – sisters, aunts, mothers, and matriarchs – appear to simulate oestrus in order to show their innocent family members how to act, enabling them to avoid the pitfalls of poor mating choices.
If I said you had a beautiful trunk, would you hold it against me? (photo: WildlifeDirect, Dzanga Forest Elephants)
After hearing anecdotal accounts of this behavior, a team led by Lucy Bates of the University of St. Andrews decided to dig deeper by taking advantage of an invaluable resource – a comprehensive multi-decade database cataloging the daily life activities of 2,200 Amboseli elephants compiled by Cynthia Moss, Joyce Poole, and other researchers as part of the Amboseli Elephant Research Project (AERP).
Bates and her colleagues systematically combed through 28 years of detailed AERP records and located all occasions on which an observer had concluded that an identifiable elephant was in oestrus (based on postural and behavioral changes in females, interactions with males, etc.). In total, they found descriptions of 999 oestrus events, slightly less than 10% of which (98 events) recorded two or more members of the same elephant family displaying simultaneous oestrus behavior.
Next, the researchers cross-referenced these accounts with AERP demographic records to find any that must have been “false” oestrus events, which they defined as oestrus-like behavior by a female who was either already pregnant, in a state of lactation-induced infertility, or senescent (which they deemed to be the case if she was over 50 years old, had not given birth to any calves during the prior five years, and had no subsequent calves).
They discovered that, while false oestrus behavior was relatively rare (occurring only 19 times and representing only about 2% of all recorded oestrus events), its timing was fascinating. Very often, it occurred just when a young relative was coming into oestrus for the first time.
Even though simultaneous oestrus behavior had been recorded less than 10% of the time, over half of the false oestrus events (10/19) clearly occurred at the same time as the true oestrus of a young female family member who had never given birth. Further, subsequent birth records confirmed that on four additional occasions a false oestrus event occurred during the month that a young relative conceived her first calf (that is, the young female must have been in oestrus at the time, even though it wasn’t specifically called out in the AERP database). Finally, one of the false oestrus events occurred simultaneously with the genuine oestrus of a female relative who had given birth before. Thus, the large majority of the false oestrus events – 15 of 19 – coincided with true oestrus events, in most cases, the first oestrus of a young relative. (Moreover, note that the balance of the false oestrus events could also have coincided with true ones if, as in the four cases described above, the true oestrus event simply had not been observed or recorded in the AERP database.)
The researchers then examined various hypotheses that might explain the false oestrus behavior:
That false oestrus merely results from hormonal changes and has no functional purpose;
That it somehow induces sexual receptivity in the simulating female, thereby increasing her own chances of successfully reproducing;
That it indirectly benefits the simulating female by providing a young family member with increased access to suitable males (this type of indirect benefit is known as an inclusive fitness benefit); or
That it indirectly benefits the simulating female by encouraging a confused younger relative to engage in more suitable oestrus behavior (another potential example of inclusive fitness).
They quickly rejected the all but the final hypothesis. For one, hormonal changes couldn’t adequately explain either the observed patterns (false oestrus occurred in both pregnant and non-pregnant females, as well as during all stages of pregnancy) or the higher-than-expected coincidence of false oestrus with the genuine oestrus events of inexperienced relatives. Second, it was clear that the simulating elephants weren’t improving their own reproductive success: in 14 of 19 cases the simulating the female was already pregnant, and in four others she was senescent. Third, AERP records revealed that false oestrus behavior had no impact on the number of available males, the relative percentage of males who were in musth, or the amount of sexual activity engaged in by inexperienced female.
Ultimately, the researchers concluded that:
Further data is required to confirm or reject the hypothesis that this behaviour functions to teach the young, naïve females, but we suggest that it remains the only viable possibility based on the current analyses.
In particular, they noted that additional research and data collection was necessary to explain the instances in which false oestrus didn’t appear to coincide with an inexperienced relative’s oestrus as well as to support the notion that inexperienced females were able to correct substandard mating behavior after they were shown what to do by their older relatives.
In the meantime, though, you’d be well advised to stay away from those frivolous young guys and find yourself a dashing older bull who knows his way around the herd.
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Bates, L., Handford, R., Lee, P., Njiraini, N., Poole, J., Sayialel, K., Sayialel, S., Moss, C., & Byrne, R. (2010). Why Do African Elephants (Loxodonta africana) Simulate Oestrus? An Analysis of Longitudinal Data PLoS ONE, 5 (4) DOI: 10.1371/journal.pone.0010052.
I’ve always found friendly interactions between animals of different species to be oddly reassuring. After all, the world can’t be all that bad a place if two animals, separated by differing genetic backgrounds and behavioral imperatives, can find a way to reach across the biological divide and share something, something joyful and positive.
Because of this, I’m an absolute sucker for all of those YouTube videos of cats curling up with mice, horses who befriend sheep, elephants and dogs who are inseparable, and the like. You know the ones I mean.
Many times, though, these are artificial pairings that spring up after we humans have altered the environment, habituating or even confining the animals with one another. While these human-influenced relationships can be incredibly heartwarming, it somehow seems even more magical when animals forge connections across species boundaries in the wild, in their native habitats and without any human intervention.
With that background, I’d like to introduce a paper published last year in the journal Aquatic Mammals1, which reports on two separate playful and – as you’ll see – uplifting encounters between bottlenose dolphins (Tursiops truncatus) and humpback whales (Megaptera novaeangliae).
The first took place on a January afternoon off the northwest coast of Kauai, when a group of eight bottlenose dolphins met up with a pair of humpback whales. Two of the dolphins – apparently adults – approached one of the whales, first appearing to surf the pressure wave created by the whale’s head as it swam, and later taking turns lying perpendicularly across the whale’s rostrum when it surfaced to breathe. Then, while one of the dolphins lay balanced over the end of its rostrum, the whale stopped and slowly lifted the dolphin high into the air. The dolphin maintained an arched position and made no effort to escape, allowing the whale to continue lifting until it was nearly vertical in the water, at which point the dolphin slid down the whale’s rostrum, dove into the water, and porpoised back to its fellow dolphins.
Here’s a color photo of the dolphin just about to go whale-sliding:
Look Ma, No Hands! (photo credit: L. Mazzuca)
And here’s a black and white series of shots that captures the full adventure sequence:
The second encounter also occurred on a January afternoon, this time off the northwest coast of Maui, when an adult female bottlenose dolphin swam up to a mother humpback whale and her calf. After diving underwater, the dolphin and mother whale resurfaced with the dolphin resting across the mother whale’s rostrum. The mother then proceeded to lift the dolphin a total of six times over 8.5 minutes, with the dolphin either lying on her stomach or right side during the lifts, which varied in length from four to 45 seconds. Again, the dolphin made no attempt to escape and held her position in such a way as to facilitate the whale’s lifting.
Here’s a sequence of photos showing this second duo demonstrating the proper technique for lifting a relaxed-looking dolphin:
The authors of the Aquatic Mammals paper considered alternate explanations for these interactions, including whether they represented an aggressive whale response to an antagonistic dolphin approach, whether the whales were demonstrating concern regarding perceived distress in the dolphins, or whether the cetaceans were simply playing together. They found the first two hypotheses to be unlikely – among other things, the interactions were too cooperative and relaxed in pace to be aggressive, and the dolphins were in good health and showed no evidence of distress. In the end, while the authors didn’t rule out the possibility that maternal instinct was involved in the whales’ lifting behavior, they concluded that the best explanation was that these were simply instances of interspecies play between the bottlenose dolphins and humpback whales.
Further, these bouts of play between dolphins and whales may not be all that uncommon, as back within the friendly confines of YouTube I was able to locate a video documenting another episode in which a bottlenose dolphin went for a ride on the rostrum of a humpback whale:
…
Play may serve a number of important purposes – for example, it may provide an avenue for intelligent, social animals like dolphins and whales to experiment with their surroundings, hone their physical skills and learn how to interact collaboratively with others. But aside from any practical evolutionary significance, I like to think of these encounters as illustrating how animals can, on occasion, take a few minutes away from the serious business of survival to share some pure joy and wonder with a fellow being, even a fellow being of a different species.
So, all of this is comforting. If dolphins and whales (and other animals who form interspecies bonds) can find a way to communicate playfulness with each other and to share experiences without any kind of a common language, perhaps we humans can do a bit better ourselves. Maybe some of the divides we see today – political discord, religious conflict, international posturing, cultural and racial inequities – aren’t so unbridgeable after all. Perhaps all we need to do is to remember an uplifting dolphin story or two.
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1Deakos, M., Branstetter, B., Mazzuca, L., Fertl, D., & Mobley, J. (2010). Two Unusual Interactions Between a Bottlenose Dolphin (Tursiops truncatus) and a Humpback Whale (Megaptera novaeangliae) in Hawaiian Waters Aquatic Mammals, 36 (2), 121-128 DOI: 10.1578/AM.36.2.2010.121.
“Ha ha ha,” politely hoots the chimpanzee, not exactly rolling on the floor. He’s not laughing spontaneously or for very long, but he does want to encourage his playmate to keep up the antics.
Continuing on in the spirit of last week’s post on the rodenty laughter of tickled rats, today’s post features a recent study on social laughing in chimpanzees.
As we all know quite well from experience, human laughter is a many-faceted thing. Sure, we sometimes laugh spontaneously and joyously (this is known as Duchenne laughter), but we also use our laughter as a multipurpose social tool, enabling us to establish rapport with social partners, to announce that we are nonthreatening and open to further communication, to alleviate tension and break barriers when meeting an unfamiliar face, and even to exclude others by demonstrating scorn or derision. In short, laughter sends a wide range of communicative signals, and our mastery over its many varieties lies close to the core of what’s sometimes referred to as emotional intelligence – the sophisticated way in which we assess, understand and navigate social situations.
Well, do any other animals manage their laughter for social reasons, or is nonhuman laughter inevitably spontaneous and reactive, like the high-pitched chirping of tickled rats? (Not that this would be a bad thing, just ask the rats….)
Marina Davila-Ross and her co-researchers from the University of Portsmouth decided to test some chimpanzees to find out. They studied 59 male and female chimpanzees of all ages living in four separate colonies at the Chimfunshi sanctuary in Zambia – two smaller colonies that had formed within the past five years, and two larger ones that had been together at least 14 years. In general, the chimps in the colonies that had been together longer belonged to more established families and had grown up with more opportunities to play with others in a familiar social environment.
Did you see the look on Mr. Mookimbo’s face when he bit into the “cake”? (photo credit: David Eppstein)
First, the researchers videotaped almost 500 one-on-one play sessions, documenting what the chimps did and when they laughed. The researchers recorded spontaneous laughter as well as laugh replications (laughter that followed within five seconds after a playmate’s laughter), and further noted whether the laugh replications occurred during the first second (rapid laugh replication) or within the next four seconds (delayed laugh replication).
The research team soon discovered that the chimps’ spontaneous laughter was substantially different than their laugh replications: the laugh replications were much shorter, consisting of significantly fewer calls per laugh series. Among other things, the researchers also found that:
Chimps in the more recently-formed colonies replicated the laughter of their playmates more frequently than did the chimps in longer-established colonies, even though the aggregate amount of all laughter in each of the colonies was relatively comparable.
Infants generally engaged only in spontaneous laughter, with little or no laugh replication.
Play bouts lasted significantly longer when they were accompanied by laugh replications than when they weren’t.
Laugh replications peaked at two discrete points, first at about .7 to .8 seconds after the initial laugh, and then again between 2 and 3 seconds after the initial laugh.
Next, the researchers tried to verify whether laugh replications were specifically triggered by a playmate’s laughter, and not just coincidentally associated with it. They combed through their previously-recorded video footage and, for specific chimps and their playmates, found matching play scenes that generally lined up very closely in terms of specific behaviors (chasing, tickling, grabbing, wrestling, gnawing, hitting, jumping, game playing, etc.), but that differed in one important respect – in one scene, the chimp’s playmate engaged in a potentially-triggering bout of laughter; in the other scene, it did not. When the researchers reviewed these paired scenes, they found that a chimp was significantly more likely to laugh in those scenes in which the other chimp laughed first, suggesting strongly that replicated laughter really was triggered by the playmate’s laughter as opposed to any other aspect of the chimps’ play behavior.
Well, one thing’s for sure, they’re not going to trust us with *next year’s* holiday decorations… (photo credit: Christa Saayman)
Based on their findings, the researchers concluded that chimps laugh in response to the laughter of their playmates, that this laughter differs in acoustic form and timing from their spontaneous laughter, and that the purpose of their non-spontaneous laughter appears to be to prolong social play, promoting group cohesion and perhaps providing the chimps with important social advantages.
In support of these conclusions, the researchers also observed that the lack of laughter replication in infant chimps suggests that socially managed laughter is a skill that chimps learn as they mature. Further, they hypothesized that the chimps in the newer colonies may have engaged in more replicated social laughter because they were living in a less predictable social environment and may have had a greater need to manage laughter in order to establish social cohesion.
So, next time you’re at a party with a group of laughing chimpanzees (don’t think I don’t know you, AnimalWise readers), listen very closely to the rising levels of laughter around you. While you might be tempted to believe that you’re hanging out with a particularly hilarious crowd, the truth may be that your fellow party goers are simply adept at using laughter as a social lubricant. Let the good times roll!
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Davila-Ross, M., Allcock, B., Thomas, C., & Bard, K. (2011). Aping expressions? Chimpanzees produce distinct laugh types when responding to laughter of others. Emotion, 11 (5), 1013-1020 DOI: 10.1037/a0022594.
“Let’s go tickle some rats.” With those epic words, neuroscientist Jaak Panksepp and his undergraduate assistant, Jeff Burgdorf, went into their Bowling Green State University lab to engage in the hard work of science.
Panksepp, who had been studying play behavior in young human children as well as 50-kHz ultrasonic chirping noises made by juvenile rats during rough-and-tumble play, had just put two and two together: “I had the ‘insight’ (perhaps delusion) that our 50 kHz chirping response in playing rats might have some ancestral relationship to human laughter.”1
The rest has been history, and today Panksepp is undoubtedly the world’s foremost authority on rodent tickling:
…
As they progressed with their research, Panksepp and his colleagues found that many of their rats seemed irresistibly drawn to tickling, chasing after the ticklers and making substantially more play chirps while being tickled than during any other behavior. But the researchers weren’t content with anecdotal observations, and over the course of several years and a number of experiments, they systematically documented a dozen separate lines of evidence suggesting that the rats’ tickle chirping corresponded behaviorally to playful laughter in young human children.2
No, I went "chirp, chirp, chirp." If I'd been laughing, it would have been "chirp, chirp, chirp."
They compiled data establishing, among other things, that certain areas of the body are particularly ticklish (the nape of the neck, for you do-it-yourselfers), that the most playful rats tend to be the most ticklish, that rats can become conditioned to chirp simply in anticipation of being tickled, that tickle response rates decline after adolescence, that young rats preferentially spend time with older ones who chirp more frequently, that the tickle response appears to generate social bonding, that chirping decreases in the presence of negative stimuli (such as the scent of a cat), that rats will run mazes and press levers to get tickled, etc. Based on their research and observations, Panksepp and his fellow researchers hypothesized that rats, when being tickled or engaging in other playful activities, experience social joy that they vocalize through 50 kHz chirping, a primordial form of laughter that is evolutionarily related to joyful social laughter in young human children.
Does it look like my name is Elmo?
It’s safe to say that the neuroscientific community did not exactly rush to embrace this hypothesis. Behavioral neuroscience can be a particularly conservative and skeptical field, one that has traditionally been extremely wary of any theorizing about emotions controlling neural processes or behavior in animals. Since subjective experiences cannot, after all, be measured directly, it has been considered far more appropriate to those functional brain activities and processes that can be scanned and measured objectively, and to simply deny or ignore the possibility that animals experience complex emotional states such as joy, at least in the context of scientific research. As Panksepp put it:
Of course, it was hard to publish this kind of work, and it was ironic that the publication of our initial manuscript was impeded by prominent emotion researchers, some of whom take pains to deny that we can ever know whether animals have any emotional feelings.3
Hahaha, we've had our little fun now, haven't we? If you tickle me again, I'll pee in your coffee.
Fortunately, time and scientific progress have been on Panksepp’s side. We have identified an increasing number of common underlying structures and processes (homologies) in the brains of humans and other mammals and, as brain scanning technologies have become more sophisticated, we have gained greater insight into neural activities triggered in connection with particular emotional experiences. While the ability to cognitively “get a joke” may depend on our incredibly advanced human neocortex, we now believe that much of the foundational brain circuitry relating to laughter, mirth, social joy, social play and emotional processing lies deep within subcortical regions, where our brains are much more similar to those of other animals.
At this point, Panksepp and his colleagues recognize that they have not definitively proven their hypothesis, but their view is essentially that they have made a reasonable case that fits their data and that hasn’t been disproved:
Until someone can offer us some data that falsifies our hypothesis, we believe our theoretical approach better reveals the true nature of the underlying processes than any intellectual scheme that simply constrains itself simply to the accurate description of the environmental and neural control of behavioral acts.4
Even acknowledging the understandable caution of neuroscientists and the obvious difficulty in drawing scientific conclusions about the subjective experiences of animals, it does seem entirely plausible (and not overly surprising) that social animals such as rats would enjoy playful romping and tickling, and that they might vocalize their pleasure in a way that was somewhat akin to basic human laughter. In fact, we hope and fully expect that, as our knowledge of comparative brain structure and function grows over time, we will see more and more studies that show clear linkages between the minds and brains of humans and other animals.
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1Panksepp, J. (2007). Neuroevolutionary sources of laughter and social joy: Modeling primal human laughter in laboratory rats Behavioural Brain Research, 182 (2), 231-244 DOI: 10.1016/j.bbr.2007.02.015.
2Panksepp, J., & Burgdorf, J. (2003) “Laughing” rats and the evolutionary antecedents of human joy?. Physiology & Behavior, 79(3), 533-547. DOI: Panksepp, J., & Burgdorf, J. (2003). “Laughing” rats and the evolutionary antecedents of human joy? Physiology & Behavior, 79 (3), 533-547 DOI: 10.1016/S0031-9384(03)00159-8.
A group of red-footed tortoises ran away (rather slowly) with the 2011 Ig Nobel Prize in physiology1, bringing to center stage the potential link between contagious yawning and empathy in animals. While the Ig Nobels are a tongue-in-cheek spoof of the Nobel Prizes, their purpose is not frivolous – they “honor achievements that first make people laugh, and then make them think. The prizes are intended to celebrate the unusual, honor the imaginative — and spur people’s interest in science, medicine, and technology.” Here’s the story of the tortoises’ claim to fame and what we know about contagious yawning in animals.
Tortoise yawning? I don’t think so!
It turns out that the underlying cause of contagious yawning has been something of a puzzle – why is it that when you see someone else yawn (or even hear a yawn or just think about yawning), you sometimes are overcome with the urge to yawn yourself? The most common hypotheses are that contagious yawning results either from empathy or from non-conscious social mimicry, the tendency to adopt a social partner’s postures, gestures and mannerisms. An alternative hypothesis, however, is that it may simply reflect a fixed action pattern, an innate or instinctual response to a stimulus (a triggering yawn).
No, really, go on - I'm listening... (photo: Peter Baumber)
And that’s where the red-footed tortoises lumber into the picture. Lead researcher Anna Wilkinson and her colleagues figured the tortoises would offer a good way of testing the fixed action pattern hypothesis, since they are known to yawn and respond to social stimuli, but are not believed to exhibit empathy or engage in non-conscious social mimicry.
The researchers worked very hard to induce contagious tortoise yawning, spending six months training one of them (Alexander, if you’re curious) to yawn whenever he saw a red square-shaped symbol, and then devising a series of tests to see whether six “observer” tortoises would yawn after seeing Alexander yawn. Initially, the observers were presented with three scenarios: one in which they watched Alexander giving one of his patented yawns, another in which they watched a non-yawning tortoise (Alexander?), and a third in which they simply viewed Alexander’s red square. A second experiment mirrored the first, except this time the observers watched Alexander yawn multiple times. Finally, they went to the movies, seeing clips of real tortoise yawns, fake yawns and an empty background.
And the results? Nothing, nada, zilch. The tortoises simply didn’t yawn more frequently after seeing another tortoise yawn; no contagious yawning whatsoever. This spectacular display of non-yawning in tortoises led the researchers to “suggest that contagious yawning is not simply the result of a fixed action pattern and releaser stimulus …. We suggest that contagious yawning may be controlled through social processes such as nonconscious mimicry or empathy….” Naturally, international acclaim ensued.
Apes and Monkeys and Dogs, Oh My!
So, which animals do demonstrate contagious yawning? Well, as with other cognitive realms, our views of contagious yawning have followed “AnimalWise’s Rule”: first we believed it to be an exclusively human behavior, then we observed it in chimpanzees, then we saw it in monkeys, next in dogs, now … hmm … Taste it, fur-face, I have opposable thumbs! Ok, I lied, that’s not a real rule; I just made it up.
Here’s a run-down on what we actually know about contagious yawning in non-humans:
Chimpanzees
The phenomenon was first demonstrated in chimpanzees in 2004 when a research team led by James Anderson of the University of Stirling reported2 on a small study in which six adult female chimps watched video scenes of other chimps who were either yawning naturally or, alternatively, displaying open-mouthed facial expressions that weren’t yawns. Two of the observers (33%) yawned significantly more often in response to the yawn videos and none of them yawned more frequently in response to the open-mouth control videos, a response rate only slightly lower than that in humans watching comparable videos. In 2009, Matthew Campbell and colleagues from the Yerkes National Primate Research Center (YNPRC) expanded on these findings, reporting3 that, much like humans responding to on-screen yawns by Pixar characters, a group of 24 chimps yawned significantly more often after watching 3D computer animations of yawning chimps than after watching animations of chimps displaying non-yawn mouth movements. Finally, Matthew Campbell and Frans de Waal of the YNPRC reported4 this year on an experiment lending empirical support to the hypothesis that contagious yawning stems from empathy. Campbell and de Waal found that, consistent with studies showing that humans demonstrate greater empathy towards others they view as being similar, chimps yawned significantly more frequently in response to videos of familiar chimps yawning than they did to either videos of unfamiliar chimps yawning or videos of chimps (regardless of familiarity) who were at rest.
…
Monkeys
The first study supporting contagious yawning in non-ape primates was published5 in 2006 by University of Stirling researchers Annika Paukner and James Anderson, who had 22 stumptail macaques watch video clips of other macaques either yawning or making non-yawn facial movements. Although the macaques yawned significantly more in response to yawn tapes than to non-yawn tapes, the researchers noted that the macaques engaged in more self-directed scratching (a tension-relieving behavior) while watching the yawn tapes, making it difficult to differentiate between actual contagious yawning and the release of stress perhaps brought on by the yawn tapes. The case for non-hominid contagious yawning was bolstered in 2009, though, when Elisabetta Palagi of Pisa University and her colleagues published6 a study in which they recorded and reviewed over 3,200 baboon yawning displays (all occurring in the absence of stressful events or behavior). They not only found clear evidence of contagious yawning among adult baboons, but also discovered that females (but not males) tended to match the type of yawning display (baboons make different facial expressions when yawning) that had triggered their own yawn, and that the degree of contagiousness correlated with social closeness, thus supporting an empathy-basis for yawn contagion and anticipating the results of 2011 chimpanzee experiment described above.
Dogs
Lastly, in 2008 Ramiro Joly-Macheroni and colleagues from the University of London reported7 on an experimental first on multiple fronts: yawn contagion in a non-primate species and the first demonstration of possible contagious yawning across different species. In their study, 29 dogs observed an unfamiliar human either yawning or making non-yawning mouth movements, with 21 dogs yawning in response to the yawning human and not one yawning in response to the human who displayed the non-yawning control behavior.
Future Directions
I know that if the Internet were allowed to vote, researchers would spend much of their waking hours considering YouTube videos of impossibly cute kittens yawning, but I want to take this opportunity to call for a full and serious investigation into the concerning link between contagious duck wing flapping and odd French Canadian music:
…
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1Wilkinson, A., Sebanz, N., Mandl, I., & Huber, L. (2011). No evidence of contagious yawning in the red-footed tortoise Geochelone carbonaria. Current Zoology, 57(4), 477-484.
2Anderson, J., Myowa-Yamakoshi, M., & Matsuzawa, T. (2004). Contagious yawning in chimpanzees Proceedings of the Royal Society B: Biological Sciences, 271 (Suppl_6) DOI: 10.1098/rsbl.2004.0224.
3Campbell, M., Carter, J., Proctor, D., Eisenberg, M., & de Waal, F. (2009). Computer animations stimulate contagious yawning in chimpanzees Proceedings of the Royal Society B: Biological Sciences, 276 (1676), 4255-4259 DOI: 10.1098/rspb.2009.1087.
4Campbell, M., & de Waal, F. (2011). Ingroup-Outgroup Bias in Contagious Yawning by Chimpanzees Supports Link to Empathy PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0018283.
5Paukner, A., & Anderson, J. (2006). Video-induced yawning in stumptail macaques (Macaca arctoides) Biology Letters, 2 (1), 36-38 DOI: 10.1098/rsbl.2005.0411.
6Palagi, E., Leone, A., Mancini, G., & Ferrari, P. (2009). Contagious yawning in gelada baboons as a possible expression of empathy Proceedings of the National Academy of Sciences, 106 (46), 19262-19267 DOI: 10.1073/pnas.0910891106.
7Joly-Mascheroni, R., Senju, A., & Shepherd, A. (2008). Dogs catch human yawns Biology Letters, 4 (5), 446-448 DOI: 10.1098/rsbl.2008.0333.
In our man-made world, it can feel like everything is converging all at once. Indistinguishable glass skyscrapers sprout up in cities all over the globe, near identical car models vent carbon dioxide into the air on different continents, and people around the world see their waistbands expand as they gulp down the same McFood. Global economies are more connected than ever, with natural disasters in Japan, sovereign debt issues in Europe, and rumors of Wall Street misdeeds shaking worldwide markets within minutes. Even the social media that deluge us with information seem like they’re growing more and more alike, as we now drown in unending streams of look-alike feeds, postings, messages and links from Twitter, Facebook, Google+ and others.
You may wonder whether the forces of convergence are a recent phenomenon, a product of human technology, or whether they may have deeper roots in the natural world. In fact, convergence can and does occur in the realm of biological evolution, albeit at a more comfortable pace. For example, “convergent evolution” occurs when different species independently evolve similar solutions to comparable evolutionary pressures. A classic example of this is the development of wings and the ability to fly by birds, bats and pterosaurs:
Diagram of wing morphology and/or and comparative network hub structure of Twitter, Facebook and Google+ (image credit: National Center for Science Education)
Consider also the independent evolution of sleek, torpedo-shaped bodies by fish, cetaceans and ichthyosaurs:
Sleek ocean swimmers (image credit: All About Reptiles)
Closer to home, scientists at the Max Planck Institute for Evolutionary Anthropology have concluded that we may be undergoing a process of cognitive convergent evolution with dogs based on our social relationships over thousands of years with these “best friends” of ours. In a paper published in Trends in Cognitive Sciences, Brian Hare and Michael Tomasello reviewed a large number of studies focused on canine, human, and non-human primate social and communicative skills and reached some interesting conclusions.
Proof of convergent canine-human evolution (source unknown)
They began their analysis by focusing on research showing how well domestic dogs do at interpreting human social and communicative behavior. For example, dogs excel at tests in which experimenters hide food in one of several opaque containers and then signal where it has been hidden by pointing, gazing, bowing or nodding, or placing markers in front of the target location. The dogs easily interpret this type of cue, passing tests such as these on the first attempt and performing correctly even when humans try to trick them by walking towards the wrong container while pointing in the opposite direction to the correct container.
Also, studies have shown that dogs are aware of what humans can see. For instance, if a human turns around during a game of fetch, the dog will almost invariably bring the ball back around the human and drop the ball in front of his face. Similarly, dogs have shown that they prefer to beg for food from humans whose eyes are visible than from ones whose eyes are covered with a blindfold or bucket, but are more likely to approach forbidden food when a human’s eyes are closed.
Indeed, dogs actually consistently outperform chimpanzees and other primates at these types of skills, even though, in areas of non-social cognitive performance, dogs do not do so well. For example, non-human great apes are much better at making inferences about the location of hidden food based on non-social cues (such as a tilted board that might be tipped up by hidden treats) and at tests that require them to achieve food rewards by, for example, reeling in food attached to strings.
With this in mind, Hare and Tomasello turned to whether domestic dogs’ specialized social skills are likely to be due to convergent cognitive evolution with humans or whether another explanation is more plausible.
First, they considered the possibility that dogs learn to recognize human social cues based on their experiences growing up in human households. They found, however, that studies show that even puppies as young as nine weeks old are adept at solving problems using human pointing and gaze cues, and that puppies raised without much exposure to humans are equally skilled at interpreting these cues.
Then, they considered whether domestic dogs may have simply inherited their social skills based on their common ancestry with wolves, since wolves are, after all, pack hunters who need to be able to follow complex social interactions with other wolves and with prey. However, although wolves are generally equal to or better than domestic dogs at memory tests and tasks involving general problem-solving abilities, wolves (even those raised by humans) are simply unable to match the performance of dogs at spontaneously using human social cues to solve problems.
Next, the researchers sought evidence for the evolution of social skills in dogs through their long-term relationship with humans. They looked at a population of domesticated foxes, where the selection for breeding had been based solely on the tendency of individual foxes to be non-aggressive and fearless around humans. Interestingly, these foxes were just as adept as dogs in using and interpreting human social cues, and far better than a population of control foxes that had been bread randomly with respect to their attitude towards humans.
Based on all of these comparative findings, Hare and Tomasello concluded that the best explanation for dogs’ specialized social skills is that they evolved as a consequence of dogs having been domesticating by humans, representing a case of convergent cognitive evolution. Interestingly, Hare and Tomasello went further and, based on their review of the research on domesticated foxes, concluded that the evolution of specialized social skills in domesticated dogs may actually have been an incidental byproduct of an initial decision to select based solely on nonaggression (as opposed to social intelligence).
Finally, turning to primate evolution, Hare and Tomasello speculated that a similar process may have contributed to differences between human and chimpanzee social skills. Under what they refer to as the “emotional reactivity” hypothesis, they predicted that differences in temperament between humans and other primates may help explain some of humans’ extraordinary social cognitive abilities. They point to studies showing that chimpanzees’ willingness to cooperate with each other can often be limited by lack of social tolerance for one another resulting from fear and/or aggression, and contrast this to a more socially tolerant temperament that may ultimately have enabled our hominid ancestors to develop flexible forms of cooperation and communication. In other words, humans underwent a form of self-domestication leading to greater social abilities, thereby convergently evolving with our canine companions who were undergoing the same process.
I’m not sure I entirely buy the notion that we humans are so exceptionally tolerant, but I have noticed that you’ve started to look a bit like your dog. In a future post, we may look at whether we may also be evolving to be more like members of the cat family:
Which one is the lion? (source unknown)
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Hare, B., & Tomasello, M. (2005). Human-like social skills in dogs? Trends in Cognitive Sciences, 9 (9), 439-444 DOI: 10.1016/j.tics.2005.07.003
Wilkinson, A., Kuenstner, K., Mueller, J., & Huber, L. (2010). Social learning in a non-social reptile (Geochelone carbonaria) Biology Letters, 6 (5), 614-616 DOI: 10.1098/rsbl.2010.0092.
paulfnorris
AnimalWise 