Out all day shopping for that perfect gift for your bestie?  Relish in the joys of reciprocal altruism this holiday season.  Reciprocal altruism occurs when unrelated individuals give each other some sort of benefit, such as food, a festively wrapped item of clothing, or maybe even cash (insert hint to friends here).

Robert Trivers developed the theory of reciprocal altruism in the early 70s in an attempt to explain why organisms help each other when there is no genetic relatedness between them.  The basic idea is “you give to me, and at some point I will give you back even more in return.”   Reciprocal altruism occurs under certain conditions: when two organisms have the ability to remember each other, and these two individuals can interact repeatedly over long periods of time. In general, the cost of the gift is lower than the ultimate benefit received from sharing.

Many primates are capable of displaying reciprocity.  This makes a lot of sense because primates tend to live in social groups where individuals are not always related, and social interactions occur at frequent rates.  In vervet monkeys (Cercopithecus aethiops), females can form friendships with unrelated individuals.  However, females in the group do not always get along (gasp!).  When fights between females break out, the female combatants begin calling loudly for back-up.  Who shows up when there’s about to be a girl fight?  Primarily the females’ relatives, but friends that were recently groomed by the fighters may also get involved to lend assistance. A little gift of grooming to a friend can guarantee big benefits when support is needed most.

Chimpanzee males sometimes share highly prized food items such as meat with unrelated individuals.  Food sharing can solidify alliances, guarantee later reciprocal gifts of food, or even secure mating privileges.

Below is a video of a male chimpanzee securing a papaya from a tree and sharing it with an unrelated female.

Happy holidays to you, your kin, and all your social acquaintances!

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Sources: Seyfarth, R.M. & Cheney, D.L. 1984. Grooming, alliances, and reciprocal altruism in vervet monkeys. Nature 308, 541-543.

Hockings KJ, Humle T, Anderson JR, Biro D, Sousa C, et al. (2007) Chimpanzees Share Forbidden Fruit. PLoS ONE 2(9): e886. doi:10.1371/journal.pone.0000886

Although scientists have yet to determine the exact function of the yawn in humans, some research suggests that yawning was used in our evolutionary past as a communication signal of some sort. Perhaps it was a means of showing off ones large teeth in a threat display or simply a way to signal to everyone that it is time to move on in search of greener savannas. We tend to yawn more when we are bored, but boredom alone does not account for many of our yawning incidents. Athletes yawn while working out, babies yawn while in utero, and we often yawn in response to seeing, hearing, or even thinking about yawning. This “contagious yawning” phenomenon was of interest to researchers at the Yerkes National Primate Research Center, who set out to better understand why chimpanzees yawn when they see other chimpanzees letting out their ho-hums. (For the article, click here.)

In the study, 23 chimpanzees (Pan troglodytes) from two separate groups were allowed to view videos of other chimpanzees either yawning or just simply hanging out. (Check out the video below…even chimps can’t seem to  turn away from the i-phone!)  As expected, chimpanzees routinely yawned in response to seeing other chimps yawn, but the interesting part was that the chimpanzees yawned more when watching their friends and family yawn than when they watched strangers yawn. What does this mean?

The researchers think the results support the idea that contagious yawning is related to empathy–or the ability to recognize and share the feelings of others.  Humans tend to have more empathy for our loved ones and people more like us than we do for complete strangers or people not like us. So, the more empathy we have for someone, the more empathetic behaviors we show them. If yawning is a symbol of empathy, then we would expect close group members to contagiously yawn more often around each other.  Indeed, it has been shown that in other primates (ex: gelada baboons), the closer the social bond between two monkeys, the more they contagiously yawn around each other.

So, a fun experiment for you amateur primatologists would be to let out a big yawn and then note which people tend to yawn the most in response. Are the strangers that yawn back at you more empathetic individuals than others?  If your friends don’t yawn back, are they really your friends??? What else could explain the differences in amounts of contagious yawning?

(Disclaimer: we are not personally responsible for any severed relationships due to a failure to yawn on another individual’s part.)

Reference:

Campbell MW, de Waal FBM, 2011 Ingroup-Outgroup Bias in Contagious Yawning by Chimpanzees Supports Link to Empathy. PLoS ONE 6(4): e18283. doi:10.1371/journal.pone.0018283

Check out this popular YouTube Video of a chimpanzee showing a little excitement at the zoo.

So…what’s going on here? Is the chimp happy, angry, annoyed? Although we can’t know for sure since it is impossible to get into this little guy’s head, scientists can use what we know about wild chimpanzee behavior to proffer a guess as to why he seems to be “going crazy.” Below is a video excerpt from Discovery.com which offers one scientist’s point of view on the display.

With everyone abuzz about human primates heading back to school this month, it seems only fitting to discuss the phenomenon we call social learning. Generally speaking, humans are social-learning junkies, and we spend billions of dollars annually to ensure that we are well educated and that our educators are educating us well, er–good.

So, why do we send children off to school so soon after they get into their big-kid pants?  In addition, why do we spend much of our adult lives in some sort of  classroom, i.e. taking courses, muddling through training seminars, hey, how ’bout another spring conference, anyone?  Do other primates relish in their own “edu-ma-cation?”

Nonhuman primates vary in regard to their social learning abilities and time spent learning in the social setting. All primates are relatively gregarious, so it is fitting that they are capable of learning by observation of others, particularly during their juvenile days when youngsters soak in their mother’s behavior, emulating her food choices, social displays, and other habits.

Have you ever eaten at a friend’s house and thought, “whoah, this is some strange food?!?” Your friend, meanwhile, happily cleans her plate, eventually noticing your reluctance only to ask, “well, don’t you like it?” The types of food you tend to enjoy are heavily influenced by the food you are given when you are young and what you observe others around you eating on a regular basis. Young orangutans eat the same foods as their mothers, but not all youngsters eat the same foods. (Link to article here.) Even tiny infant marmosets are capable of solving feeding tasks more quickly when they are able to watch their mothers perform the task first. (Read more here.) Primates learn much of our most basic behavior from mimicking our parents.

In addition, many primates can learn from individuals outside of their immediate family groups, and the presence of multiple group members while we learn can be an advantage when it comes to learning time. Capuchins presented with new problems in the lab can solve them quicker while surrounded by other capuchins than they can when working on the tasks alone. The ability to watch others fail and learn from their mistakes, as well as to copy what works right are two key aptitudes that allow many primates to learn efficiently. When in the social setting, we also learn how to behave by being chastised by the group when we do not do what is expected. Primates continually acquire knowledge throughout their entire lives, learning by individual experience, but just as important, by making observations of and having interactions with others.

Although social learning is evident in some form in all primates, one aspect of social learning that hasn’t been studied long enough to truly understand is the art of active teaching. While it is quite obvious that individuals in most (if not all) primate groups do learn from each other, it is hard to demonstrate that nonhuman primates actually teach their youngsters in the same manner that humans do. However, some research does seem to suggest that some form of teaching does occur in nonhuman primate groups. For instance, in our aforementioned marmoset example, Momma Marmoset belabors feeding tasks when her infants are present, but breezes through them when she is alone or with older animals. This suggests her concern for making sure that the infants can perform the job properly before she moves on. It will be exciting to see more studies such as this one come about.

So, with our kiddos heading back to school with vigor, remember to think about all the little primates out in the world, right now actively participating in their own social learning experiences. Oh, and on a side note…don’t forget to thank your mom that she fed you good stuff, not like that weird food at your poor friend’s abode.   What was that, anyway? Custard?

Would it surprise you to know that other primates get tipsy, drunk, and even high? What if you found out that the percentage of nonhuman primates that choose to partake in drugs and alcohol usually mimics the numbers that we see in human societies?

Spanning several decades, research on rhesus macaques has shown us that some monkeys will readily drink alcohol whenever it is offered, and some will try it once but never again. Some primates tend to be social drinkers, while others prefer to drink alone.  And human primates aren’t the only ones that experiment with other types of drugs besides alcohol. Some Black Lemurs (Eulemur macaco) rub the secretions of toxic millipedes on their bodies, which acts as a narcotic on them, causing excessive salivation and apparent “spacing out.” Although the evolution of this behavior is hard to explain since it likely makes the lemurs more vulnerable to predation, it appears that the millipede secretions not only make the lemurs feel funny but also act as an insecticide, protecting them from biting insects and any of the diseases such pests may be carrying.

Baboons, spider monkeys, and macaques are just a few of the other types of primates that have been seen stumbling back to their sleeping sites after having one too many pieces of fermented fruit.

Take a look at this video featuring vervet monkeys with constant  access to alcoholic beverages on their home island of St. Kitts.

Human preferences for drugs such as alcohol seem to be substantially influenced by our genes, and these genetic inclinations are mirrored in other primates. However, unlike the vervet monkey societies where drunkards seem to be well respected by group members, human societies tend to denounce drug addiction and alcoholism. Or do they? Feel free to discuss!

Who’s the boss here? Mama Lemur, of course! Ring-tailed lemurs have the distinction in the animal kingdom of being one of the few species of mammals that display true female dominance. When a female wants to sit in a particular crook of a tree currently occupied by a male tenant, a mere guttural grunt on her part causes the male to jump up and move out of the way.

Simple seating preferences can cause a male to hop to attention, but feeding time is even more relegated. When encountering a new feeding site, adult males sit on the outer edges of the group while females and youngsters rush in and feast on all the good stuff. After a time (the amount of which is determined by female tolerance of said males), the males will eventually work their way into the group to feed. I have seen many instances where males often do not even get to feed until the females have moved off from the site! Females rarely have to use extreme forms of aggression to maintain their position as top boss. Instead, young males seem to learn the pecking order as they undergo puberty, a time during which all the females in the group continually remind them of their place by chasing them away from food, biting them, and clucking angrily when they get out of line.

This type of female authority over males is actually unusual as far as mammals go. In most mammalian species, males tend to be larger and physically stronger than females. Females do not often challenge male authority since physical confrontation would result in significant male advantage and potential bodily damage to the female or her babies. Disparity in strength between the sexes has to do with the way the mammalian body uses its energy supplies. Most energy in the female body goes to the task of raising babies…getting pregnant, supplying nourishment to the developing fetus, undergoing the physical birth, and spending months nourishing a growing infant, only to begin the process again after weaning the infant(s). Energy in the adult male body, on the other hand, goes towards anything that helps the male to find a mate. In many animals, this means males grow large and strong so that they can fight amongst each other for access to cute females! The simple advantage of physical power usually leads to males having priority over females when it comes to food and water sources and resting and sleeping sites.

However, growing big is costly! Just as bodybuilders cannot reach their large size without eating thousands of calories of protein a day, any male animal has to be able to get enough calories, vitamins, and minerals on a regular basis to grow large bodies. Are you surprised to know that in most animals with female dominance (including lemurs), males and females  are similar in body size, with males only slightly larger (if at all) than females?!? How can this be explained? There are several theories, one of the most well-known being that when food is extremely limited, male and female body sizes tend to be more equalized, simply because there isn’t enough available energy around for males to “get pumped.” Most available food in the territory goes to female’s energy requirements for raising babies, and it makes sense that natural selection would favor a situation where a female gets first dibs on the quality food since survival of the species is dependent on her ability to raise offspring.

Several other lemur species also have female dominated societies, and various primate species such as bonobos, squirrel monkeys, patas monkeys, gibbons, bush babies, lorises, sifakas, indrids, and owl monkeys have systems where females can be the boss or at least have equal opportunity to compete with males for resources. What about humans, you may ask? Stay tuned for future posting on the power of the female in human societies.

In the animal world, there is an overwhelming tendency for these West Side Story lyrics to ring true: “One of your Own Kind/Stick to your own kind!” However, primates in captivity will readily associate with members of different primate species, human caretakers, and even other types of animals entirely. Koko the gorilla proved the tenderness of the primate spirit with her acceptance and motherly treatment of the kitten “All Ball,” and monkeys have also been seen attempting to raise kittens as their own babies. Why share food with a member of another species? It’s a type of tit for tat strategy, meaning that the primate that does the sharing benefits in some way from the partnership. Maybe making an unusual friend will offer you protection, social company, or food at a later date, and thus the costs of losing a little food are outweighed by the potential benefit of a long-term relationship. Human primates have taken this strategy to the ultimate level, domesticating animals that have been associating with us for thousands of years, as is the case with dogs. Presumably, wild dogs offered our ancestors protection from predators by standing guard near human camps and warning of intruders. In return, the dogs were allowed to feed on scraps that humans tossed to them from their camp. Known as a mutualism, a situation gradually evolved in which both humans and dogs received benefit from the arrangement,which eventually led to the domestication of hundreds of dog species.Dogs didn’t have to work as hard for food, and humans were able to train dogs to work for them. Watch below as an orangutan and dog form an unlikely but heartwarming partnership.

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