Monkey Medicine

The mountainous kingdom of Nepal, in southern Asia, contain some of the world's most breathtaking mountain scenery. More astonishing, though, are the antics of the macaques (members of the Eurasian monkey family), who live in the region. These primates have the strange habit of digging holes in the ground with their delicate fingers. When they reach a certain depth, the monkeys scoop up the earth at the bottom of the hole - and eat it.

Bernadette Mariott, an American scientist, has looked into this phenomenon. At first, she thought the monkeys were eating the insects or worms living in the soil. Then she noticed that the macaques were interested in the soil itself. After conducting a soil analysis, researchers were able to solve the riddle. It turns out that the soils of the macaque's habitat are rich in minerals, and have a particularly high concentration of kaolin, a substance which hinders diarrhoea. Somehow, the monkeys discovered the medicinal effects of the soil, and begun to treat their ailments with it.

Primate Self-Medication

The primate world is full of surprises. A good example are the chimpanzees that live deep in the mountains of Tanzania, in East Africa. Japanese researchers have documented the actions of a large female chimpanzee, which was obviously weak and in poor health, but which was able to find a natural medicine.

The animal did not have the strength even to pick up the ants that were within reach on the ground. Instead, she gathered her last reserves of strength and dragged berself to a little grove of trees. There, she grabbed a bunch of leaves of the tropical plant Vermonia amygdalina and chewed them carefully to get at the plant's bitter juice. Apparently, the juice acts to ease cases of stomach and digestive upsets. After administering this natural medicine, the chimpanzee spat out the leaf fibres.

From a discreet distance, the Japanese researchers watched this amazing scene. The next day, they noticed that the chimpanzee was in good health and fed completely normally. Impressed by their discovery, they formulated a daring hypotheses, namely that primates such as the chimpanzees are able to heal themselves.

Further observations of chimpanzees in other parts of Africa have lent support to the Japanese hypotheses. Generally, primates feed from fruits in the immediate vicinity, but they sometimes undertake a 20-minute walk in order to find a plant called aspilia, which belongs to the aster family. This plant is certainly no delicacy, for the apes make a disgusted face and turn up their noses when they chew the leaves. At one point, researchers even surprised a male as it spat out bits of half-chewed plant.

What makes chimpanzees eat such foultasting food? Perhaps it is good for them. Together with biologists, primate researchers have analysed the red, oily juice contained in Aspilia. To their great surprise, they found that it contains a substance which destroys prasites and fungi - making it a kind of natural antibiotic.

Scientists from Japan and the United States have also noticed that chimpanzees eat more healing plants during the rainy season - the period when pneumonia and other infectious diseases are particularlay threatening. This seems to imply that our primate cousins are aware of the health risks.

Contraception

Alleged evidence of birth control has resulted in a more careful reaction from scientists. Here, attention has focused on the behaviour of the howler monkey (genus Alouatta), a group of primates which is indigenous to the Americas. For some time after birth, female howler monkeys in Brazil frequent a certain tree species, which has not yet been named. The monkeys eat a considerable quantity of the leaves, which contain certain chemical substances known as isoflamines, whose effect is similar to that of oestrogen dan probably reduces the fertility of the females. Could this be a type of plant contraceptive?

Because monkey medicine is a very new field of research, there are potentially many surprises in store. So the scientists organised conferences to share their findings, and extended their studies to other regions.

They soon found, for example, that some female howler monkeys in Costa Rica - a small nation in Central America - eat a herbaceous plant before and after mating, which they do not consume at any other time. Even though there is as yet no prood, researchers suggest that the females may use the plant to regulate their fertility, since they do not register any births in these periods.

Pick A Gender

Of all the hypotheses so far put forward by primate researchers, the most far-fetched stats that pregnant howler monkeys may be able to determine the sex of their young ones. More than 20 years of observation has demonstrated that, at a certain period, a large percentage of the females give birth to male offspring only. At other times, however, only females are produced. Again, scientists found that these femalses had eaten certain plants before and after mating. They suggest that the plants affect the acidity of vaginal mucus, perhaps inhibiting conception.

Managing The Population

What is uncertain is the monkey's reasons for determining the gender of their babies. The answer may be found in the complex structure of primate societies. In a troop of howler monkeys, only the males have a chance of eventually assuming a leadership role. Thus, a mother could secure a privileged position for herself within the group by producing male offspring. In the same way, when there is a shortage of females, the female who is responsible for producing loffspring could strengthen her position in the hierarchy by producing female young (which will, in turn, become mothers) since this goes a long way towards ensuring the survival of the group.