When we are sick, or suffering discomfort from diarrhea or indigestion, we take medicines to make us feel better. We know what ails us, and we know what can help us. Monkeys, too, seem to have knowledge of the therapeutic. New cases are reported every year, and zoopharmacognosy, the study of self-medication in animals, is a growing field. The fur-rubbing white-faced capuchins and the charcoal-eating red colobus monkeys seen in Clever Monkeys are just two examples of medical ingenuity in primates. Across the globe, monkeys have figured out remedies for common ailments, just as we have.

One of the greatest dangers to monkeys, and one of the greatest annoyances, are insects and parasites. Ectoparasites like lice, ticks, and mosquitoes carry many diseases to which monkeys are susceptible. Evolutionary biologists believe that parasites coevolved with their hosts over eons, and both humans and monkeys have continually sought relief from these pests. Itching, scratching, and swatting are the only options for most animals, but primates have evolved several novel approaches. Grooming is an effective way to pick off pesky bugs, but the white-faced capuchins seen in Clever Monkeys take pest control to another level. They rub themselves with leaves from the piper plant, which is also used by some people in Costa Rica as an insect repellant. The piper leaves are also antiseptic, which helps ward off bacterial and fungal infections. Fur-rubbing episodes in the white-faced capuchin monkeys correlate markedly with increases in humidity. The capuchins know that increased humidity means an increase in the abundance of insects, and the risk of bacterial and fungal skin infections. Capuchins also sometimes rub their fur with millipedes that contain benzoquinones, chemical compounds that repel insects. Owl monkeys and lemurs have also been observed fur-rubbing with millipedes. Only in the capuchins does fur-rubbing play a social role. In Clever Monkeys, the white-faced capuchins become quite excited and enthusiastically gather together to anoint each other with the piper plant. What underlies this party-like behavior is a simple protective measure for the group: each member of the group benefits if the group as a whole is protected from parasites.

Primates also have to deal with intestinal parasites. Tamarins have been known to swallow large seeds that in effect dislodge and sweep worms out of their intestinal tract. This practice markedly decreases the parasitic load within their intestines. Other monkeys experience bouts of diarrhea brought on by parasites and viruses. The bonnet macaques of Southern India have taken to eating dirt from termite mounds. Why eat dirt from termite mounds? The dirt contains kaolin minerals, the same ingredient found in over the counter anti-diarrhetics such as Kaopectate. Rhesus macaques also partake in geophagy, the eating of dirt, for the same reasons. Clay also contains kaolin, and the rhesus macaques take extra care to only ingest clay-rich soils. Like the white-faced capuchins, which only select plants for fur-rubbing with insecticide properties, the macaques selectively choose the right kinds of dirt to sooth their stomachs.

Because their leafy diets contain high levels of cyanide, many monkeys, like the black and white colobus in Clever Monkeys, suffer from indigestion. The discovery by red colobus monkeys that eating charcoal absorbs the cyanide and relieves indigestion was revolutionary. The practice is transmitted from mother to infant by imitation. Knowledge is passed from generation to generation, just as the most tested and true remedies have been passed down by earlier generations of humans. With the toxins being absorbed, the red colobus monkeys are free to eat a wider array of plants that have a high nutritional value and are easily digested. The birth rates in red colobus monkeys that eat charcoal have exploded, proving an evolutionary advantage to self-medicating. It is their clever mind, their curiosity, and their novelty that have made them successful. The same could be said about us. 

Photo © Wiebke Lammers

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.

Perhaps no form of communication sends a more vivid and direct message than that of touch. Whether used to extend a friendly greeting, to soothe or support, or even to intimidate, it is difficult to misinterpret the meaning of a tactile signal.

Like all primates, chacma baboons spend a significant amount of time expressing themselves through physical contact, from reassuring touches and pats to antagonistic bites and swats.

When two individuals meet, they will cordially touch muzzles and acknowledge each other in an amiable “nose-to-nose greeting.” Chacmas also engage in “social mounting,” which is generally a response to social presenting. Though it resembles a sexual mount, the baboon has no real intention to mate. In most instances, social mounting signals friendly reassurance, but it has been noted by primatologists to occur during aggressive encounters as well.

But the one form of physical expression held sacrosanct in chacma society is “social grooming.” In addition to the hygenic benefit of removing parasites, dead skin, and debris from the fur, grooming is also thought to reinforce social bonds between animals. For the baboon being groomed, the experience of having its hair pulled is highly pleasurable, as it releases endorphins that produce a natural high. This helps to alleviate stress and build trust among members of the troop. In fact, studies have proven that the levels of stress hormones, called “glucocorticoids,” drop significantly in chacmas after they engage in grooming behavior.