Along the banks of the mighty Zambezi River in the high plains of northern Zimbabwe, a troop of chacma baboons tend to their daily routines in accordance with the rules of social order that make for a stable and cohesive community.

Alliances can mean the difference between life and death, as each day brings a myriad of challenges. Months of searing heat and drought grip the land, and ambushes by rival troops and predators such as leopards, crocodiles, and pythons pose imminent threats.

A rare set of twins born to the dominant male and female face an especially difficult trial. In an environment where only a quarter of infants survive their first year, the odds are stacked against them. But their “royal parentage” could carry some advantages for their survival.

In the Zambezi, privilege can be lost as quickly as it is gained. A large male from a neighboring troop enters their ranks, determined to unseat the dominant male. In a swift and decisive battle, the king is deposed and the entire stability of the troop is thrown into turmoil. Under the rule of the new alpha male, the twins are no longer safe — the intruder has cast his eye on their mother. But the infants are not yet weaned and until they are, their mother will remain sexually unavailable. For the tyrant, the equation is simple and brutal, but just how far will he go?

The rains are late and the dry season stretches into its eighth month. Competition for food brings the troop’s inherent rivalries to the surface, and bouts of infighting break out. The alliances that were once the binding thread of the group begin to come undone.

Meanwhile, only one of the twins has survived, and he must grapple with his brother’s murder, his father’s overthrow, and a mother whose affections have been commandeered by the one responsible for the heinous deeds.

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Online content for Murder in the Troop was originally posted April 2006.

They revel in the good times and comfort in the bad, offering one another companionship and support, strength and protection. After all, what are friends for?

That is precisely the question that a devoted sector of scientists and behaviorists are puzzling to answer. But the friendships they are concerned with are not those that develop among humans, but rather those of the chacma baboons that inhabit southern Africa’s Zambezi region.

As NATURE’S Murder in the Troop shows, chacmas live in large troops, governed by strict hierarchical order, in which alliances and family ties are the foundation. Spending a large part of their day in close proximity to one another, they engage in a host of communal bonding rituals, from grooming to foraging to collectively caring for their young. These activities serve to strengthen their social network as they build trust within the troop and buffer against outside threats such as predators or rivals. It would seem there could be no safer environment in which to raise a family.

During grooming, the pulling of hair releases endorphins.

But there is a dark side to chacma society. Desiring to father their own offspring, highly aggressive alpha males often resort to infanticide — killing baboon babies that are still dependent on their mothers’ milk. A nursing mother will not come into heat, but without a baby to feed, she will stop lactating and once again become sexually available.

“Infanticide is common in chacma baboons,” says Dr. Ryne Palombit, Associate Professor at Rutgers University’s Center for Human Evolutionary Studies. He has been studying chacma baboon troops in southern Africa for over a decade. “It is usually perpetrated by a male who has recently immigrated into the group and has attained alpha status. That is not to say that all males who accomplish these two things always attack and kill infants.”

But the attacks occur often enough to shake the nerves of every new mother in a troop. In some years, Dr. Palombit has seen troops suffer an infanticide rate of up to 75 percent of all infant deaths. So, what is a mother to do in order to avoid the risk of her baby being killed? According to Dr. Palombit, those with young offspring often seek out friendships with males. “In chacmas, just about every lactating female has at least one male friend,” offers Palombit. “I think friendships are likely to reduce the risk of infanticide, and we’re trying to identify how that happens.”

A female will develop a bond with a male solely for the protection he may offer, especially when it comes to defending her baby from an attack. “We have data suggesting that although many males may rush over to an infant when the alpha male attacks it,” says Palombit, “it is usually only the male friend of the infant’s mother who will get involved directly and actively. For example, he’ll actually fight the attacking male or scoop up the infant and run off with it.” In some instances, a male consort may take on the role of foster parent after a mother’s death.

Friendships typically involve no sexual behavior, as lactating females almost never copulate. But the relationship can benefit the male in other ways. “The female invests heavily in the relationship by keeping in close proximity to him and grooming him,” says Palombit. Furthermore, a male may gain an advantage in joining a troop if he forms an association with a female on the inside.

As their hierarchical law dictates, chacmas typically consort with those only within their own rank. But females will sometimes seek friendships with males of higher rank, as they are usually more assertive in their behavior and therefore may offer more security. But Palombit is careful to note that despite social status, some baboons are simply better protectors than others.

While friendships with males may be useful in guarding against infant death, it is important to remember that in the wild there are no guarantees. Only a quarter of all chacma babies survive their first year. And when the worst happens, bereaved mothers turn to their female friends for comfort, often using the act of grooming as a tactile form of “grief therapy.” When the fur is stroked and pulled during grooming, endorphins are released, producing a natural high that relaxes the animal.

A 2006 paper published in Proceedings of the Royal Society of Biological Sciences underscores the important physical benefits of companionship in chacma society, especially during times of loss. In a 14-year study of chacma baboons in Botswana’s Okavango Delta, researchers regularly measured the levels of glucocorticoids, a group of stress hormones, in 21 females. In humans, these levels rise after the death of a close friend or relative. The baboons who had suffered losses were found to have elevated levels of the hormones as well. The study further indicated that after the death of a family member, females compensated for their loss by “reaching out” more than usual to other females. They increased their grooming rate and broadened their circle of grooming partners — even “breaking rank” to form alliances with those beneath them. Researchers believe that the contact serves as a coping mechanism for the baboons, as their glucocorticoid levels dropped significantly just after grooming.

Not only is this study the first to provide direct evidence that some animals mourn the loss of individuals, along with the work of Dr. Palombit and his colleagues, it illustrates how social bonds reduce stress and keep the troops cohesive.

Whether they involve fiercely defending each other or offering gentle and nurturing support, one thing is certain — friendships are vital to chacma society. And though we have not yet pieced together all the intricacies of their relationships, these baboons are giving us a pretty good indication of what friends really are for.

Highly intelligent, emotional, and expressive animals, it is little surprise that elephants live by social rules that are intricate. So complex and layered are they, that in elephant society males and females live in completely different worlds, with females dwelling in tightly bonded families that stay together for life, and males living a largely solitary existence.

Elephant families like Echo’s EB family are matriarchal societies. Within this structure, the matriarch, or lead female, rules over a multi-generational family of 6 to 12 members, most of which are her offspring, her sisters and their offspring. In Echo’s family, her sister Ella and daughters, Enid and Eliot help her keep the family in order along with her nieces, Emma and Eudora, her granddaughters, Edwina and Eleanor, and great-niece, Elspeth. Sadly, as the film documents, Erin, Echo’s daughter, was speared by humans and died. A tight-knit family like the EB works very cooperatively. They feed, rest, and move as one unit. Together they defend the family, search for food and care for offspring. Closely-related females will even cross suckle each other’s calves and some females will lactate indefinitely, taking on a wet nurse role in the family. Enid, Echo’s oldest daughter, has a natural mothering instinct and love for calves. She was an allomother, or babysitter, to her younger brother, Ely.

Echo’s Family Tree: Click to view larger. Courtesy of the Amboseli Elephant Research Project

As tight-knit as they are, if an elephant family gets too large, it can split in two. This actually benefits both families as each can forage for resources more effectively if they take on different territories. Typically, such a split would take place between cousins, and usually not sisters or mothers and daughters. These split families, or “bond groups” can average 28 related elephants in 2 to 3 family units. The related groups will continue to associate and occupy the same home range, staying within a mile of each other and keeping in touch through rumbling calls.

Though all members of the family are essential for the group’s success, it is the mighty matriarch who assumes the most critical role. Typically the oldest and largest female member of the family, it is not uncommon for the matriarch to be a close relation to the previous matriarch. To succeed in her role, the matriarch brings years of experience and natural skills at leading her family and keeping all of its members together. She also has a sharpened memory of places and individuals. The adage that an elephant never forgets has some truth to it. An old female can remember where her mother or grandmother took her for water during a drought 30 years earlier, the sort of historical information that can save a herd during hard times.

Matriarchs are charged with making decisions that ensure the family’s safety, health and survival. Tapping into her years of wisdom and experience, she decides when and where to feed, when to move along, when to fight and how. Her influence is so great that if a matriarch is shot by poachers, the herd will likely remain by their fallen leader and be shot as well. In the case of Echo and her famous EB family, Echo’s regularity and as Martyn Colbeck explains, predictability may have saved the lives of the family members. During the 1970s and 1980s, the area outside of the park had a dark history of poaching of elephants traveling in large groups. Echo’s insistence on keeping her family within the range of Amboseli Park kept them safe from poachers. Deferring to the experience of a wiser and older member and forming nearly unbreakable bonds allows for the exchange of critical survival skills to the next generation.

One method elephant society has evolved to keep the family robust and healthy is by forcing out males once they reach puberty-a measure that protects against inbreeding. As they grow older and approach puberty, males, or bulls, grow increasingly independent of their family. They will eventually break off from the group, usually at around 12 years of age. Unlike the highly social females, bulls will live a solitary life, forming relatively few close and long-lasting bonds with other elephants. They travel alone or congregate with a herd of two to 14 bulls, occasionally joining a family on a temporary basis. During the breeding season, bulls wander widely, searching for receptive females. After mating is over, they leave the family and either rejoin a bachelor herd or go back to a life of solitary wandering.

Humans have had a devastating influence on elephant society. As humans kill off vast numbers of elephants and encroach on their habitats, elephants grow increasingly anxious, disoriented and, at times, violent. Since older, larger animals are more likely to be targets for poachers because their tusks are largest-and these are also the members of the family with the most critical role– killing these individuals damages entire family units for years. Due to poaching, the number of older matriarchs and female caregivers has drastically fallen, and some elephant groups contain no adult females whatsoever. The number of elder bulls, who play a significant role in keeping younger males in line, has also fallen. All of this damage within elephant societies leads to incidents of “elephant rage” or attacks on humans and their property. By understanding how killing one elephant reverberates through elephant society, humans may come to realize how great an effect they have on elephants, and on other humans.