Males in a high-oxytocin relationship were more likely to initiate cuddling, and females were more likely to initiate sex. These males were initiating the behavior that the female needed for high oxytocin, and the females with high oxytocin were initiating the behavior that male partner needed for high oxytocin.

This kind of play might be a way for young gorillas to test how far they can push their behavior and how members of their group will respond to unfair situations, preparing them for more serious interactions like conflicts over food, say researchers who studied gorillas in natural settings.
As they write in their paper:

The subjects, that hit their playmates unequally prior to a play chase, significantly more often moved first to run away than their playmates. Therefore, the current study provides, to our knowledge, first empirical evidence that non-human species may try to maintain their competitive advantages when responding to inequities. These findings suggest that humans are not unique in being sensitive to inequities when they have the advantage and the disadvantage … and in their ability to modify their responses to these situations accordingly.

Females who had the strongest, most stable, and longest-lasting relationships with other baboons lived significantly longer than those whose social ties were more fragile and unpredictable. To illustrate their findings, the researchers divided the baboons into three groups according to the quality of their relationships with others. Members of the least sociable group lived from about 7 to 18 years; the middle group lived from about 9 to 25 years; and the friendliest group lived from 10 years on up, as some were still alive when the study ended.
Such findings in a nonhuman primate, the authors write, “suggest that the human motivation to form close and enduring bonds has a long evolutionary history.”

It’s almost amusing to us. The female hears the snort and thinks, ‘oops, there is a lion.’ She steps back, and the male comes around and mates. It’s striking.

On average, the researchers say, the males earn nearly three additional mating opportunities by using a false snort to delay a female’s departure from their territory. For their part, the females are in heat for only one day a year—which may help explain why they don’t catch on to the deceptive behavior. Plus, they’re safer erring on the side of caution, given the high potential cost of thinking a “true” alarm is “false.”
The researchers conclude in their paper that:

Although firm statements about intentions behind behaviors are notoriously difficult to make, our study does identify a parallel between animals and humans in their capability of using false signaling to deceive mates, a finding that hints that their communication may be less fundamentally different than widely assumed.

The scientists decided to see what happened when they gave pairs of chimps different rewards in exchange for the same tokens—one got a carrot while the other got a grape (a sweeter, better deal). As expected, the chimps were more likely to reject the carrot when they saw their partner get a grape. This kind of “inequity aversion,” primatologist Frans de Waal has argued, is a rational response that’s linked to the fact that:

in a cooperative system, one needs to watch what kind of investment one makes and what one gets in return. If your partners always ends up getting a greater share, this means that you’re being taken advantage of. So, the rational thing to do is withhold cooperation until the reward division improves (The New York Times).

But the researchers discovered something even more interesting: The chimps were more likely to reject a grape when their partner only got a carrot. In other words, the chimps didn’t only respond negatively when they got the short end of the stick, but also when their partner got a raw deal.

So are chimps as sensitive to unfairness as humans are? Given the choice, will they make fair offers and reject unfair ones? Researchers at the Max Planck Institute of Evolutionary Anthropology don’t think so. A couple of years ago, they showed that unlike humans—who will reject an unfair division of money, even at a cost to themselves—chimpanzee responders accepted any nonzero offer, whether it was unfair or not. The only offer that was reliably rejected was the 10/0 option (responder gets nothing) (Max Planck Society).

And clearly the chimps were willing to propose unfair deals to their partners. Yet it’s worth pointing out that they were also separated from one another by cage mesh. Perhaps Brosnan’s animals rejected their “undeserved” grapes in part because they sat right next to their less fortunate partner and may have feared retaliation for their windfall, the researchers suggest (New Scientist).

If the early laboratory studies were a realistic representation of nature, nature should be overrun by hyperaggressive males—and it’s not. So something was wrong with that idea, and now we know what.

This time, the researchers used a wading pool with special doors that let the insects move freely between groups of “gentlemen” and “psychopaths,” as evolutionary biologist David Sloan Wilson calls them:

The presence of psychopaths dramatically reduced the productivity of the population. When all the males were gentlemen, the females laid about three times more eggs than they did when all the males were psychopaths. And yet within each group the psychopaths were doing better than the gentlemen. How do the gentlemen persist if they’re disadvantaged within the group?

When they opened the doors, the females would leave whenever a psychopath came around. The whole thing resulted in a heterogeneity in which the females were clustered with the gentlemen. It’s the movement of individuals that creates these differences between groups that favor nonaggressive males.

Even when the chimpanzees observed their conspecific partner unsuccessfully struggle to reach the juice container without a stick tool, the tool possessor often failed to offer the tool voluntarily unless explicitly requested.

This type of requested altruism may be more economical than voluntary altruism, the researchers suggest, since it minimizes the chance that a chimpanzee will waste an effort by helping another chimp unnecessarily.

Why test monkeys for musical traits?
One of the things that we’re interested in is how did music evolve, how did it develop in human beings? We realized that, in our own language, we add a lot of musical components to it when we’re trying to communicate emotionally. So if I say “I’m happy” in a flat tone or “I’m really sad today” in a cheerful voice,  you probably aren’t going to pay much attention to my words, but pay more attention to my intonation, the patterns of music that are in my voice. For instance, we know that if we want to calm a baby we’ll say, “Aw …” starting at a high pitch and going to a lower pitch so our notes and sounds are really drawn out.
We know as well that we can help slow down our dogs or a horse by saying [in a drawn out way]: “Whoa. Slow.” So the same patterns seem to work in terms of maneuvering the behavior in other species
That raises the question: Is this emotional communication something that may be very old and very ancient that we’ve built upon with our music to make it something much more complicated and uniquely human, but underneath it somewhere there are these basic principles that are related to emotion?

Can we trace the evolutionary roots of our emotional response to music?
My collaborator, David Teie, is a musician and a composer, and he’s been really interested in what it is about music that moves us. When we listen to a piece of music, why do we feel sad sometimes, or why do we feel cheerful and happy at other times? David’s been looking for some principles in composition that composers might use to get (or trick) us to make us feel an emotion the way that the composer wants us to. How do we test this theory? One of the problems with doing this with people is that we already have a long history of how we react to music. We know we either like rock music or we hate it. We like rap music or we hate it. We like Mozart or we hate it. It becomes very hard to look at this in humans because we already have a long learning history with our experience with music.
This led to thinking about testing monkeys, as a substitute. But then we ran into a neat little problem, which is that the monkeys, in a different study, were shown to be totally indifferent to human music. So if you gave the monkey a choice between Mozart and rock, the monkey preferred Mozart, but if you gave the monkey a choice between silence and Mozart, the monkey preferred silence. That suggested that we shouldn’t expect another species to have the same musical responses we have, but if there’s some sort of general theory involved, we should be able to show that in some other way.

By composing special music for monkeys?
We discovered as we listened to the monkeys that they have a voice range that is about three octaves higher than the human voice and their rate of calling is about twice as fast as human speech. With those features in mind, David Teie wrote some music that had these basic principles. David hypothesized that to calm an organism, we have long tonal notes that don’t have any dissonance in them, and are very clear pure tones. For arousing music, we have short staccato notes that may have a lot of dissonance added to them, which induces fear.
David composed music to express those two different aspects and we played them back to the monkeys, we found that basically they didn’t respond to the human music—we played them human calming music and some human rock music. But then we played the tamarin calming music and they calmed down. And they showed increased activity and increased anxious behavior when we played them the tamarin arousing music. This suggests that the same principles hold across a variety of animals, but in order to test these principles, we need to be aware that other species may not be hearing music the same way we hear music.

Especially when it comes to Metallica.
What we found was that when we played them Metallica—and also a piece by Tool—they calmed down after hearing it.
I have no idea why that happened. But what is nice from our perspective is that although our monkey version of Metallica got them aroused and active and even increased anxious behaviors, the human version calmed them down. It really does illustrate the point that monkeys are hearing something very different and responding in a different way than humans do to human music.

So maybe monkeys and other animals make music too, just differently than humans do?
There are some animals that people have called musical. Birds sing, and some birds have really complex songs, if we look at themes and variations as a component of music. There are some species in which a male is more attractive to a potential mate if he can sing in a complex way and especially add some variations to the theme. But that’s not communicating about emotion; it’s communicating basically to convince someone to mate with you.  And although we may use music as a mating strategy, we have a lot more things that we use music for than that.
I don’t know that monkeys are making music, in the sense of “creating,” but we did find a lot of musical structure in their own calls. When musicians heard these calls, they could say, “Oh, there’s a minor second” or “That’s a major third between this note and that note.” So the monkeys who were producing their own vocalizations were using the same sort of scale that we humans use to appreciate music or describe music. So the monkeys are doing something musical, though they’re not showing the creativity that we know that humans do with music.
There are some language-trained chimpanzees that can use symbols, so it might be interesting to see, if you gave them a keyboard to produce tones, if they would just produce random sequences or whether they would eventually produce some sort of nice chordal structure. That would be really easy to do, but I don’t know that any of the people working with symbol-using chimpanzees have ever tried that. That would be one interesting way to see if another species would create something musical.

Females who raise offspring to a reproductive age are more likely see their genes pass along, so these findings demonstrate an evolutionary advantage to strong relationships with other females. In evolutionary terms, social moms are the fittest moms—at least when it comes to baboons.

These findings, the authors write, “parallel those from human studies, which show that greater social integration is generally associated with reduced mortality and better physical and mental health, particularly for women.”