Why are Pygmies smaller than other people?

Bigger is better, right? So why in the world have Pygmies opted for smallness?

By Jared Diamond|Friday, May 01, 1992
Deep in the forest in the darkest heart of dark Africa, where little sunlight penetrates the mist and where thick foliage shades out most of the remaining light before it can reach the ground, the humid silence is broken by the sound of an elephant lumbering along a trail. Through the dim light, the great beast fails to notice, crouched in a dense thicket beside the trail, a tiny human with a rather large head, bulbous forehead, protruding eyes, and wide nose. This homunculus waits in ambush, smeared with elephant dung to conceal his own smell.

Just as the elephant steps past, the hunter darts under it. In one quick motion he thrusts a poison-tipped spear into his prey’s unprotected belly. By the time the elephant has turned to trample its assailant into human hamburger, the hunter is already concealed under tree roots in the thicket, leaving the giant beast to die an excruciatingly slow death. When it finally expires, more tiny people creep out of the dark undergrowth to carve up the carcass. Once again the little folk of the forest dance, sing, and feast on meat obtained through their hunting prowess.

Such are the exotic scenes that most of us grew up associating with the word Pygmy. Alas, as happens so often with the fantasies of our childhood, much of this scenario is turning out to be wrong. For one thing, although most of us think of Pygmies as little people living on the African continent, anthropologists usually define them as members of any human population whose adult men average less than 4 feet 11 inches in height. That means Pygmies are actually native not just to the deepest parts of the fabled Dark Continent but to other areas scattered throughout the tropics, including lands less than 1,000 miles south of the United States. Furthermore, while many Pygmies today do live in the forest, they may well have originated elsewhere; in fact, they may even have been unable to survive in the forest until recently. And finally, while most Pygmies do hunt, it turns out that they get most of their food by a less heroic method.

Our old, romantic image of Pygmies is thus changing under the impact of new research. But the picture emerging is just as fascinating and exotic--and puzzling, because we still don’t have a generally accepted answer to the most obvious question about Pygmies: Why are they small?

Pygmies aren’t just of interest as an anthropological curiosity. They’re part of a much broader concern, the question of why people differ in size. Anyone who has ever seen a professional basketball game is surely aware of the broad range of adult human body sizes. Part of this variation is, of course, individual: people within any human society differ considerably in height. For example, adults of my immediate family of European whites range from 5 foot 2 to 6 foot 3. But the differences don’t stop at the individual: there are differences in average size between entire human populations. The world’s tallest people are the Dinka of the Sudan, whose adult men average 6 foot 1. Icelanders, Polynesians, the Irish, and some North American Indians are also tall on average. At the opposite extreme, the world’s shortest people are the Efe of Zaire--one of the peoples we commonly call Pygmies--whose men and women average 4 foot 8 and 4 foot 5, respectively.

If we concentrate on the Pygmy end of this spectrum, the question "Why are Pygmies smaller than other people?" really delves into four separate areas of science. We can ask it genetically: Do Pygmies’ genes foreordain that they will be small, or is their small size entirely a result of poor nutrition? We can look at it developmentally: At what age do Pygmies fall behind other peoples in size? We can examine it physiologically: What mechanisms in the body produce that growth lag? Or we can take the long, broad view: Why did evolution program Pygmies to be small? What good, if any, does smallness do?


To understand the Pygmies, you have to understand their lifestyle. And a good group with which to begin is the smallest of the small, the Efe of the Ituri Forest, whom a friend of mine, UCLA anthropologist Robert Bailey, has been studying in Zaire for the last dozen years. The Efe spend more than half their time at temporary campsites in the forest, where the men use bows and poisoned arrows to hunt monkeys, small antelopes, and deer. However, the meat from this prey contributes only 9 percent of the Efe’s calories, while other forest products like honey and fruit yield just another 28 percent. For those of us reared to think of African Pygmies as forest-dwelling hunter-gatherers, it comes as a shock to learn where they actually get most of their nutrition: from the gardens of the Lese, the black African farmers who live just outside the forest! The Efe work for the Lese and bring them meat, honey, and other goods from the forest. In return the Lese pay the Efe with garden-grown vegetables and fruits, along with iron tools, cloth, pottery, and tobacco.

If you ask the Lese about their relationship with the Efe, they’ll tell you they own the Efe as their hereditary serfs. Socially they regard the Efe as the lowest of the low. Poor Lese men sometimes buy Efe women as wives (because they cost less than Lese wives), but it would be unthinkable for the Lese to permit one of their own women to marry an Efe man.

For a long time anthropologists accepted the Lese view of the relationship. And in fact, the Efe connive in this fiction in order to maintain their existence and freedom. Like a sailor with several wives, each in a different port, the Efe pretend simultaneously to be the serfs of several different farmers in different villages scattered many days’ walk apart. In that way, if one Lese village has a temporary food shortage, its Efe can move to another village. Most important, this curious arrangement preserves the Efe way of life. The Lese don’t interfere with it, because they profit from the Efes’ presence.

In all these respects, as well as in their appearance and their genes, the Efe are representative of the nearly 200,000 Pygmies who live in bands scattered through the equatorial African forest. Like the Efe, the other African Pygmies live as clients of neighboring farmers and speak languages derived from the farmers’, having lost whatever their original Pygmy language was. Astonishingly, it’s now clear from archeological evidence that this arrangement could have arisen only within the last few thousand years, since it was around 2000 b.c. that black farmers speaking Bantu languages began to occupy sub-equatorial Africa, expanding out of their homeland in present-day Cameroon. Before that, Pygmies probably occupied the entire humid zone of equatorial and subequatorial Africa. The encroaching farmers must have driven the Pygmies out of open savannas suitable for farming, leaving them in fragmented groups in whatever forest the farmers had not yet felled.
Despite this long history, African Pygmies are customarily thought of as having been discovered by the German explorer Georg Schweinfurth, who in 1870 met and measured seven Pygmies in what is now Zaire. But Schweinfurth no more discovered Pygmies than Columbus discovered an America already occupied by tens of millions of so-called Indians. These events are discoveries only in the sense of the first sightings by a lit- erate European, preferably an Englishman. Pygmies were already known to literate Egyptians and Greeks more than 4,000 years before Schweinfurth discovered them, and they must have been known to black Africans for untold millennia.

But even before Schweinfurth encountered the African Pygmies, European explorers had discovered other small, dark-skinned, curly-haired peoples in other areas of the old-world tropics, such as the Malay Peninsula, the Philippines, the Andaman Islands, and the mountains of New Guinea. All these Pygmies used to be thought of as genetically related members of a formerly widespread Negrito race, but that theory has since been refuted. Instead, it’s now clear that these dark-skinned Pygmies are actually several unrelated peoples who evolved small size independently. That conclusion is even more certain for the lighter-skinned Bushmen of southern Africa and for the Maya and other small-size American Indians, who are all arbitrarily classified as Pygmies because their adult men measure under 4 feet 11 inches. Thus, to ask why Pygmies evolved their small size is really to ask why many human populations in the Old and New worlds separately became very small.

Let’s start with the genetic formulation of the question: Are Pygmies small because of genetic programming, or is their size the result of poor nutrition?

There’s no doubt that childhood nutrition has a big effect on the size we attain as adults. Because of improved nutrition, people in industrialized societies today are on average taller than their grandparents; for instance, the height difference approaches six inches in Japan. Our height advantage is even more marked in comparison with the starved peoples of the Middle Ages: that’s why you have to stoop to get through the doors of medieval buildings, which were designed for the shorter people of those times. Might modern Pygmies be small because they’re the worst-nourished populations in existence today?

Poor nutrition may indeed contribute to the small size of the Casiguran Agta, a Philippine Negrito population studied by the anthropologist and linguist Thomas Headland. The Agta are noted not just for their shortness: they are also the skinniest people in the world, and they suffer childhood mortality of nearly 50 percent. Many other Pygmy populations, however, seem at least as well nourished as their taller neighbors. The Efe Pygmies studied by Bailey, for example, weigh a normal amount in relation to their height and have perfectly normal fat deposits. Their diet is rather similar to that of their Lese neighbors, since they exchange the meat of hunted animals for crops grown by the Lese. Thus, my guess would be that there’s a genetic component to the body size of most populations of Pygmies: in other words, if they were reared on our affluent supermarket diet, they’d grow up to be considerably taller than they are now but much shorter than white or black Americans.

What about the developmental question: When, or at what age, do Pygmies fall behind other people in growth rate and height? It should be easy enough to answer this question--all you need to do is measure Pygmies at different ages, or measure a few Pygmies each year from birth to adulthood, and compare the results with American or black African norms.

This is easier said than done. Yes, scientists since Schweinfurth have weighed and measured thousands of Pygmies, but the ages of those Pygmies were unknown. Pygmies have no calendar and don’t calculate age. And you can’t use European standards to guess the age of the Pygmies you measure, because nobody knows whether Pygmies grow and age at the same rate as Europeans. It’s equally difficult to select some Pygmy babies and come back to remeasure them year after year, because Pygmies are nomads and you can’t count on their being at a given place each time you return.

Until recently, the most thorough effort to cope with these formidable difficulties was made by Jan van de Koppel and Barry Hewlett. Working with Aka Pygmies in the Central African Republic, these two scientists asked Aka parents whether their babies had been born before or after various datable local events, such as the death of an important farmer who owned many of the Pygmies. Based on those age estimates, Van de Koppel and Hewlett concluded that Aka children are still normal in size at age three or four and remain similar to their black farmer neighbors in height at all ages until puberty.

That was when the Aka appeared to fall behind: it seemed that they didn’t undergo the adolescent growth spurt that most other peoples do. Nearly all of you, I’m sure, can remember those teenage years when your appetite seemed inexhaustible and each year’s new clothes were already too small a year later. I still recall vividly how physically awkward I felt at age 14; how I had to pass through doors slowly because I had grown five inches in the preceding year and still wasn’t accustomed to the new positions of my head and limbs. But for these Aka there was no clear evidence of such a growth spurt, and it therefore seemed clear that as adults they would end up much shorter than their neighbors.

If adolescence is indeed the time when Pygmies fall behind, this finding would beg the third question about their size: What is the physiological explanation for the lack of an adolescent growth spurt? Endocrinologist Thomas Merimee and geneticist David Rimoin tried to answer that by measuring concentrations of hormones in Pygmies from the same area studied by Van de Koppel and Hewlett. Since African Pygmies resemble dwarfs who are deficient in a pituitary gland product known as human growth hormone, this was the first hormone selected for study. Under standard test conditions, blood concentrations of human growth hormone in Pygmies and in normal-size people proved practically the same. However, concentrations of another hormone, called insulin-like growth factor I, were barely one-third as high in the blood of Pygmies.

In combination with the growth studies by Van de Koppel and Hewlett, these hormone measurements are of double interest. First, they suggest that a deficit of insulin-like growth factor is a physiological cause of Pygmies’ small stature. Second, and of broader interest, they suggest that high blood levels of that same growth factor might play an important role in the adolescent growth spurt experienced by the rest of us. However, these conclusions depend on growth studies of Pygmies whose ages were only estimated.
In 1980 Bailey began a long-term study that was finally able to pin down Pygmies’ ages. Unlike previous workers, Bailey was actually present to record the birth dates of the babies of Efe Pygmies and their Lese neighbors; he didn’t have to rely on estimates. Then, every six months, Bailey and his colleagues returned to locate and remeasure as many of those babies as possible. By the age of five, each baby had been measured an average of four times.

In contrast to the findings of Van de Koppel and Hewlett, Bailey’s data showed that the Efe are already small at birth: they are close to a pound lighter and nearly an inch shorter than their black neighbors. As they grow, the Pygmies fall progressively further and further behind. By age five they have all of the proportionate size deficit--when compared to whites from the United States--that they will exhibit as adults. After the age of three months, no Pygmy baby’s measurements ever reached even the third percentile on the growth charts for U.S. white female babies. By the time the Pygmy children had turned five they had grown only as tall as the average two-and-a-half-year-old girl in the United States.

Bailey’s oldest subjects are now starting to reach the age of puberty. For the moment, then, it remains uncertain whether they will fail to undergo an adolescent growth spurt, as the other researchers believed. It’s already clear, however, that Pygmies are born small, immediately start to fall further behind, and would end up as Pygmies even if they were to experience an adolescent growth spurt. By the same token, the question of the physiological basis for Pygmy body size and the normal adolescent growth spurt must still be considered up for grabs.

Regardless of the genetic influences, developmental patterns, or physiological mechanisms by which Pygmies end up small, the final question remains: Why would natural selection program them to be that size at all?

If populations of Pygmy-size humans were found randomly scattered throughout the world, we could dismiss small size as an evolutionary accident. It might just have happened that some human populations were begun by a few very short people, and other populations by a few very tall people, who passed on their genes for height to their descendants. Actually, though, most Pygmies live near the equator. This suggests that some factor or factors peculiar to the tropics favored the evolution of small body size in humans.

One obvious feature of the tropical rain forest is a constantly hot, humid climate. As Stanford geneticist Luigi Ca-valli-Sforza has noted, climate may well influence body size. His reasoning is based on the elementary fact that we produce heat through physical exercise. (We sedentary nerds may tend to forget this, but marathon runners are acutely aware of the risk of heat exhaustion on a hot, humid day.) In a cool climate our bodies lose the heat produced by exercise through radiation, convection, or evaporation. In a dry climate (even in a hot, dry climate) we lose almost all our heat as the sweat from our skin evaporates into the air. However, heat dissipation becomes a serious problem in the hot and humid interior of the tropical rain forest, where the high temperatures make radiation or convection ineffective, and the moisture-soaked air doesn’t allow much sweat to evaporate. When I am working in the New Guinea jungle, I feel like a simmering pot even when I stand still, and I feel myself suddenly overheating as soon as I start walking.

The difficulties of heat dissipation increase with body size because of a simple geometric consideration. Heat production is roughly proportional to body mass--the amount of muscle available to generate heat- -which increases with the cube of linear dimensions like your height. But heat loss is proportional to body surface area--the amount of skin available to release that heat--which increases only with the square of your linear dimensions. So as people get bigger there is a greater discrepancy between the amount of heat produced during exercise and the amount they can lose. Hence bigger folk have a greater risk of overheating. For African Pygmies, as well as many other Pygmy populations of southeast Asia and the Philippines, notes Cavalli-Sforza, this becomes particularly important since they spend so much time inside the hot, humid rain forest. Thus, small body size might have evolved as an adaptation to the climate of the tropical rain forest.

While this is likely to have been a significant factor in Pygmy evolution, it was probably not the only one. Some Pygmy populations don’t even live in hot, humid habitats. Bushmen, for instance, spend their lives in hot, dry, desert habitats, where heat dissipation by sweating is efficient. And in New Guinea the theory is turned on its head, since the people in the tribes of the cold mountains--such as the oxymoronically named Goliath Pygmies, who dwell on Mount Goliath--are smaller than the people in the tribes of the hot lowland rain forest. This is exactly the opposite of what should have happened if heat dissipation were the main determinant of body size.

There’s another reason that the rain forest climate is unlikely to be the sole evolutionary reason for Pygmy body size: the Pygmy populations now living in tropical rain forests are unlikely to have evolved there. I already mentioned that the African Pygmies studied by Bailey obtain almost two-thirds of their calories in the form of crops grown by neighboring farmers. This is because, while they can get meat and honey in the forest, the Pygmies recognize that they would starve if confined there. In fact, none of the Pygmies that Bailey studied remained in the forest, away from the food sources of farming villages, for more than six days. Based on this and other evidence, Bailey suggests that most tropical rain forests provide too little edible food for any population of human hunter-gatherers, tall or short, to have survived there--until the arrival of nearby farmers to subsidize them. (See Happiness in a Hellhole, in the May 1991 DISCOVER.)

Bailey therefore reasons that African Pygmies evolved at the boundary between the rain forest and the savanna, which is much richer in game and edible plants. Several thousand years ago conditions in the Ituri Forest area were drier than they are today, and more of the area would have been savanna rather than unbroken rain forest. When Bantu farmers invaded the area, the Pygmies retreated into the forest--both because they were driven out of the open savannas that the farmers wanted to use and because trade with the farmers let the Pygmies survive in the forest. Thomas Headland makes the same argument for the Agta Negritos of the Philippines, who were driven into the rain forest by the arrival of Austronesian farmers with whom they now trade forest products in return for rice.

If Bailey and Headland are correct, then the rain forest Pygmies we see today are not preserving a forest hunter-gatherer life-style practiced for tens of thousands of years, as other anthropologists have tended to assume. Instead, these rain forest Pygmies are commercial hunter-gatherers who only recently became able to survive in the forest through trade with farmers. By this reasoning, heat dissipation would assume less importance in the evolution of small body size: on the savannas, heat dissipation by sweating is efficient, and the larger Bantu farmers can live comfortably.
If all this is true, then what factors besides the risk of overheating could have contributed to the evolution of small size in those Pygmies now living in tropical rain forests, or the Pygmies living in New Guinea’s mountains, or the Bushmen of the desert?

An alternative explanation strikes me every time I try to crawl behind some diminutive Papuan hunter through New Guinea’s infernally dense mountain forests. I’m always banging my head against a low branch, or getting tangled up in the thick vegetation, while the mountaineer is squeezing comfortably through. I can vouch for Pygmy size being a great adaptation for living in the New Guinea mountain forest, where people my size are just big, clumsy oafs. Similarly, Bailey found that Efe men spend 9 percent of their waking hours perched in trees in search of honey. That’s a safe occupation for Pygmy men who weigh, on average, under 100 pounds, risky for 150-pound whites like me, and lethal for Polynesians weighing over 200 pounds. In the immortal words of the boxer Robert Fitzsimmons, The bigger they come, the harder they fall.

Also, there’s the evolutionary explanation that since smaller people need less food than bigger people, they are more likely to maintain their body weight and avoid death by starvation during times when little food is available. That same explanation helped scientists understand why starvation killed more men than women in the snowbound Donner Party of pioneers heading for California (see Living Through the Donner Party in the March issue).

Therefore, populations of small people should have an advantage over populations of big people in habitats where food resources can’t be counted on. I’d guess that that’s another important reason for the small size of New Guinea mountaineers and Kalahari Desert Bushmen, both of whom live in notoriously unproductive environments. And insofar as other Pygmies did use the rain forest before farmers arrived to subsidize them, the advantage of small size for escaping starvation may also be relevant there. Although we think of the tropical rain forest as the world’s most luxuriant habitat, most of that biomass is actually inedible or inaccessible to humans.

In retrospect, it’s not surprising that the evolutionary explanation for Pygmyhood proves not to hinge on a single factor. We’re all aware that body size affects our lives in many ways. In addition to the advantages of being small, there are the counterbalancing advantages of being big, not the least of which is relatively greater strength and thus an edge in physical competition with small people. But because these trade- offs vary with geographic location or life-style, so does the optimal human body size favored by natural selection.

I began this piece with the exotic image of Pygmies on which I was reared--as elephant hunters dwelling inside the African forest. Our emerging understanding of Pygmies, however, tells us they are far more complex than this romantically simple image. Yet all the new discoveries take nothing away from the fascination exerted by these smallest of people, the most numerous surviving group of hunters on Earth. Pygmies are no longer to be dismissed as curious freaks. Instead, they’re of universal significance in our efforts to understand what determines the growth and size of all of us, big or small.
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