A Different Kind of Animal

How Culture Transformed Our Species

Robert Boyd

• Verlag: Princeton University Press
• Jahr: 2017
• ISBN:
  9781400888528
• Thema: Biological Sciences
• Thema: Evolution

How our ability to learn from each other has been the essential ingredient to our remarkable success as a species Human beings are a very different kind of animal. We have evolved to become the most dominant species on Earth. We have a larger geographical range and process more energy than any other creature alive. This astonishing transformation is usually explained in terms of cognitive ability—people are just smarter than all the rest. But in this compelling book, Robert Boyd argues that culture—our ability to learn from each other—has been the essential ingredient of our remarkable success. A Different Kind of Animal demonstrates that while people are smart, we are not nearly smart enough to have solved the vast array of problems that confronted our species as it spread across the globe. Over the past two million years, culture has evolved to enable human populations to accumulate superb local adaptations that no individual could ever have invented on their own. It has also made possible the evolution of social norms that allow humans to make common cause with large groups of unrelated individuals, a kind of society not seen anywhere else in nature. This unique combination of cultural adaptation and large-scale cooperation has transformed our species and assured our survival—making us the different kind of animal we are today.Based on the Tanner Lectures delivered at Princeton University, A Different Kind of Animal features challenging responses by biologist H. Allen Orr, philosopher Kim Sterelny, economist Paul Seabright, and evolutionary anthropologist Ruth Mace, as well as an introduction by Stephen Macedo.

CHAPTER 1

NOT BY BRAINS ALONE

The Vital Role of Culture in Human Adaptation

STARVATION IN A LAND OF PLENTY

In 1860, the worthies of the city of Melbourne organized an expedition to explore Australia’s interior, which was then unknown to white Australians. Their motives were mixed. Some hoped to find a route for a telegraph line that would connect Australia to Java, and then to the rest of the world. Others were motivated by rivalry with Adelaide, which had organized a similar, unsuccessful expedition a year earlier. They recruited Robert Burke, a dashing former military man, as the leader along with eighteen others, including William Wills, a scientist and cartographer. On August 20, the expedition set off with twenty-six camels, twenty-three horses, enough food for two years, and much Victorian impedimenta including oak dining furniture. The lead elements of the party, including both Burke and Wills, reached Cooper’s Creek, a long string of ephemeral ponds about six hundred kilometers north of Melbourne, by November 11 and waited there for the rest of the party. By mid-December, the stragglers still had not arrived, and Burke had had enough. He, Wills, and two others, Charlie Gray and John King, set off hoping to reach the Gulf of Carpentaria and return in three months. Burke ordered the remainder of the party to wait for them at Cooper’s Creek until March 15. Unfortunately, it took four arduous months to reach their goal and return, and Gray died along the way. When Burke, Wills, and King returned to Cooper’s Creek in mid-April, they found the camp abandoned. They were exhausted and so low on provisions that they had no chance of covering the six hundred kilometers between Cooper’s Creek and home. About this time, they were visited by a group of men from an Aboriginal group, the Yandruwandha, who, seeing their pitiable state, gave them six kilograms of fish. After a couple of weeks, they again encountered a group of Yandruwandha and accepted an invitation to their camp, where they were provided with more fish and cakes made from the seeds¹ of an aquatic fern called nardoo. The three white men liked the cakes and decided that if they were to survive, they must learn how to make nardoo flour. However, they had no idea what plant the seeds came from, and by then the Yandruwandha were nowhere to be found. After two weeks of desperate searching, Wills discovered the source of the nardoo seeds, and the three men began to collect and grind the seeds to make nardoo flour in quantity. However, despite having plenty of nardoo to eat, they gradually weakened, and by early July both Burke and Wills were dead. King was found by a Yandruwandha band that fed and cared for him for several months until a relief party arrived in September.²

So, why did Burke and Wills starve in what was a land of plenty for the Yandruwandha? The answer to this question holds the key to answering the much bigger question that is the focus of this essay: How did humans come to be such an exceptional species? Five million years ago our ancestors were just another, unremarkable ape. Today, our species dominates the world’s biota. We occupy every part of the globe, we vastly outnumber every other terrestrial vertebrate, we process more energy than any other species, and we live in a wider range of social systems than any other creature. The key to this transformation is that people adapt culturally, gradually accumulating information crucial to survival. Central Australia was a land of plenty for the Yandruwandha because they were heirs to a rich trove of culturally transmitted knowledge about how to make a living there. As we will see, Burke and Wills died because they did not have access to this knowledge. In this essay, I make the case that our species has evolved the ability to adapt culturally, and this has, for better or worse, made us a different kind of animal.

ARE THE DIFFERENCES BETWEEN HUMANS AND OTHER ANIMALS REALLY THAT IMPORTANT?

Many of my colleagues from evolutionary biology don’t think so. Of course, they would concede, people differ from other animals in lots of ways: we make much greater use of tools than any other creature; human language allows us to send a vastly larger range of signals than other animals; people have much bigger brains for their body size than most other mammals. But so what? Lots of animals have exceptional traits: elephants have long, flexible trunks, hummingbirds can hover, and indigo buntings navigate by watching the position of the stars. Moreover, we have a long history of thinking that we are different (and better) than other creatures, and many of our “unique” traits have turned out not to be unique at all. Biologists take great delight in disproving any claim that takes the form “only humans can do X.” Toolmaking, language, farming, culture, teaching, and warfare have all suffered this fate.

How should we decide whether the differences between humans and other animals are important? Are humans really exceptional? Or are we just another unique species? I think that the best approach is to choose the same zoological criteria that we use to compare the ecological importance of other species, things like species range, biomass, and energy processing. If people really are different from other animals on these dimensions, then it’s plausible that there is something anomalous about human adaptation that is worth investigating.

Let’s start with species range. The geographical range of a species is the area that it occupies; its ecological range is the set of habitats it lives in. Both are useful because they give a rough measure of how adaptable a species is. All other things being equal, a species with a larger range must be able to function in a wider range of environments. Humans have the largest geographical and ecological range of any terrestrial vertebrate. Most terrestrial vertebrates occupy part of a continent and are limited to a modest range of habitats. Our closest relatives, the apes, are good examples. Orangutans and gibbons are limited to dense rain forest in Southeast Asia, gorillas and bonobos to moist forests in tropical Africa, and chimpanzees to forest and woodland in roughly the same parts of Africa. Big predators have the largest ranges; gray wolves occupy most of Eurasia and North America outside the tropics.³ People live in every terrestrial habitat except Antarctica.

You might think that human expansion across the globe was a recent phenomenon made possible by agriculture and industrial production. But this is not the case. By the beginning of the Holocene, ten thousand years ago, hunter-gatherers had occupied every part of the globe except Antarctica and a few remote islands, and they lived in every kind of environment from the moist rain forests of Africa to the harsh deserts of Central Asia and the icy shores of the Arctic Ocean.

At this point, I’m sometimes asked about rodents: Don’t they have a worldwide range too? And the answer is yes, they do. But rodents are an order that includes more than 2,200 species, almost all with much smaller ranges. Humans are different. One species, Homo sapiens, occupies virtually every terrestrial habitat on the planet. Norway rats are an exception, but one that proves the rule. Their range is almost as large as the range of humans (they don’t survive in the Arctic). However, these creatures were limited to Central Asia until the Middle Ages and spread to the rest of the world by hitchhiking on human transport.⁴ Norway rats and other human commensals (mites, helminths) live in similar human-created habitats everywhere.

Other standard zoological criteria tell the same story. Among vertebrates, human biomass⁵ is exceeded only by that of our domesticates and is many times the biomass of all wild terrestrial vertebrate species combined.⁶ The large human biomass is not just the result of agriculture and industrial production. It has been estimated that the carrying capacity for hunter-gatherers was about seventy million at the beginning of the Holocene.⁷ This large biomass is notable because in many environments human foragers are top predators who hunt the largest animals in their habitat. Top predators are typically less numerous than their prey. For example, it has been estimated that at the beginning of the Holocene, lions—another large predator with a sizable range—numbered only about one million individuals.

The key to this ecological success is our ability to adapt to a wide range of different environments. Rodents live in virtually every habitat, but there are lots of different rodent species because rodents are specialists. Different species have different adaptations that allow them to succeed in particular environments.⁸ Beavers have webbed feet and flat tails adapted to life in the water. Flying squirrels have large membranes that allow them to glide from tree to tree. Kangaroo rats have specialized kidneys that allow them to survive in deserts without having to drink water. Salt marsh mice can drink saltwater. And it’s not just morphology.

Different species have different social behaviors adapted to their particular environments. Some are always monogamous, while others are highly promiscuous. Many species are solitary, but others, like beavers, prairie dogs, and naked mole rats, live in cooperative groups. In contrast, humans are generalists, able to adapt to a vast range of different environments and to develop local knowledge, specialized tools, and a wide variety of social arrangements.

Much human adaptation involves artifacts, but it is not just the ability to make artifacts that allows us to adapt to a wide range of environments. Many other animals make artifacts—bird nests, beaver dams, termite mounds, and the like—that play important roles in their lives. The technological sophistication of some of these artifacts rivals anything made by humans until the last few thousand years. The hanging nests of weaverbirds are beautifully designed and are at least as complex as the thatched dwellings made by many foragers. However, members of each weaverbird species construct a narrow range of nests.⁹ What makes humans special is the ability to make many different kinds of artifacts that are appropriate in many different habitats. Humans, members of a single species, make different kinds of shelters in different places—houses made of snow, sod, stone, thatch, and wood that conform to many different designs, each well suited to the local environment.

Taken together, this evidence indicates that humans are exceptionally good at adapting to a wide range of environments. The obvious question is, why?

BRAINS ALONE AREN’T THE ANSWER

The standard, somewhat self-congratulatory answer to this question is that we are successful because we are very smart. Most treatments of human evolution take this account for granted. More complex tools, more sophisticated foraging, and symbolic behavior are all taken as indicators of increased cognitive ability.¹⁰ For example, the archaeologist Lynn Wadley and her colleagues found that people living at Sibudu Cave on the coast of southern Africa about seventy thousand years ago used adhesives to fasten stone points to wooden shafts to make spears or arrows.¹¹ Their experiments demonstrate that these adhesives were made by mixing and heating acacia gum and red ochre, and that this procedure makes a better adhesive than plausible alternatives.

They conclude:

Our experiments intimate that by at least 70 kya . . . these artisans were exceedingly skilled; they understood the properties of their adhesive ingredients, and they were able to manipulate them knowingly.¹²

There are two claims here. The first is that these artisans were extremely skilled. This follows directly from the fact that making and using adhesives is a complicated business. The second claim is that they were skilled because they were smart enough to understand the properties of these adhesives. As we shall see, the truth of the first claim does not imply the truth of the second.

Most people studying human evolution aren’t very clear about exactly how intelligence translates into behavior and what intelligence really means in evolutionary terms. The simplest idea would be that we adapt to our environment just like other species, only better. Other species adapt to their environment in two ways. First, they change genetically. Individuals that live at higher latitudes are typically larger than members of the same species that live at lower latitudes, and this difference is adaptive because larger bodies are better at conserving heat. Natural selection favors differences in the distribution of genes influencing body size in populations living at high and low latitudes. Similarly, natural selection could favor certain behavioral adaptations (e.g., the ability to fling a spear) in one environment and other behavioral adaptations (e.g., the ability to ambush prey) in another environment. But natural selection is a relatively slow process, so genetic differences cannot explain why the people at Sibudu Cave used adhesives made from acacia gum while Aboriginal Australians used spinifex resin.

This leads us to the other form of adaptation: the flexible adjustment of behavior and morphology to the local environment during an animal’s lifetime. In vertebrates, learning is especially important. Individuals learn where to find food, what to eat, and who will allow them to share a food patch, and they flexibly adjust their behavior in response to the local environment. This allows them to adapt rapidly to changing environments and enables a single species to occupy a diverse range of habitats.

It’s important to understand that learning works mostly at the individual level ...