Critical Thinking Questions
- 1. Based on your reading of this chapter as well as other materials outside of class, identify the most important consequences, both good and bad, of biocultural evolution for the future of our species. For each consequence you name, write a sentence that explains why it is important. Compare your list with that of your classmates and discuss the differences.
- 2. Assess the impacts of human population growth on humans, other living things, and the earth over the past 10,000 years. Write a paragraph describing the obligations each of us shares to change these impacts. Compare your paragraph with that of your classmates and discuss the differences Identify and evaluate the global impact of human biocultural evolution.
- ▶ Express the obligation everyone shares to be stewards of the earth and its plants, animals, and resources for the benefit of future generations.
Australia’s Great Barrier Reef is a UNESCO World Heritage Area, an honor that places it on a par with other sites of “outstanding universal appeal,” such as the Statue of Liberty and the Grand Canyon in the United States. Its status as a world landmark aside, the Great Barrier Reef is hurting. A recent Australian government study (Reef Water Quality Protection Plan Secretariat, 2011) estimates that the reef annually receives 34,000 tons of dissolved nitrogen from agricultural fertilizer runoff, about 62,000 pounds of pesticides, and nearly 19,000,000 tons of sediments (of which roughly 15,500,000 tons are the product of human activity). Given these data, it is painfully obvious that humans are killing the Great Barrier Reef, not maliciously, not from indifference, but slowly and surely nevertheless. The Australian government recognizes the severity of the environmental effects and is working to reduce humangenerated pollution of the reef. It will not be an easy task. The Great Barrier Reef illustrates an important point about humans: We’ve become rather dangerous to ourselves, other living things, and the earth itself. This textbook has given you the background needed to understand how and why this happened. In Chapter 1, we observed that modern humans are cultural and biological beings whose present and future reflect their past. But where did we come from? And how did we create the present? Answers to such questions can help us understand some of our strengths and limitations as a species and, if used wisely, inform decisions that will affect our future. Our story of the human past, which we traced over 15 chapters, closes with a look at some of the consequences of biocultural evolution, perhaps the most chilling of which is our new-found ability to trash the planet. We touch only on a few key issues because the topic is another textbook in itself. Our goal is to impress upon you how unique our species has become and what this can mean in practical terms for the quality of your life, your children’s lives, and the wellbeing of the communities in which we all live.
Human Success and the Anthropocene
Humans are the most successful species ever to inhabit the earth. Sounds like a wild claim, right? After all, there are vastly more bacteria than humans, and bacteria are literally everywhere, including inside of us! But it’s true. The earth has never witnessed the rise of a species quite like humans. The most telling measure of our success is that we humans grew to be a major force of nature over the last 10,000 years, and our global impact accelerated greatly during the past couple of centuries. Geologists and other scientists are beginning to hammer out a new concept, the Anthropocene, the geological epoch during which human behavior became one of the earth’s major geomorphological and geological processes (e.g., see Crutzen, 2002; The Economist, 2011). The Anthropocene concept implies that millions of years from now, long after humans have vanished from the scene, the record of our brief existence will be a distinct geological formation, formed by a unique set of processes that we largely created and left indelibly stamped on the earth. Now that’s success, perhaps in a blunt instrument sort of way, we admit, but no other species can lay claim to the global effects that we have already achieved, whether it be our impact on the Great Barrier Reef, the air we breath, or our next drink of water!
Consequences of Biocultural Evolution
We owe our success to biocultural evolution and our primate ancestry. Without them, all this would have never happened. To explain why, let’s examine how our past informs our present and future.
Hominins to the End of the Ice Age
Glimmers of our future success are not easily found in the fossil record of our australopith ancestors (see Chapter 9). For millions of years, these hominins were just another primate on the African savanna. If we had to point to one thing that made them stand out from their primate cousins, it was that they walked erect on their two hind limbs; they were bipedal. This peculiarity aside, the australopiths were successful in the same biological sense as any other animal—they survived and successfully reproduced. The game changer for our ancestors, whether they were australopiths or early Homo, was our first rudimentary attempts at technological solutions to problems between roughly 3 and 2.5 mya. This, along with the behavioral changes that accompanied tool use, launched an adaptive process that eventually became a distinctive part of the life history strategy of early hominins. The core components of hominin biocultural evolution took a long time to develop. For hundreds of thousands of years, we were tool-assisted hominins living in small groups that were spread thinly across the landscape. The rate of biocultural change was so slow that a thousand generations could pass, and yet the tool kits of each succeeding generation looked basically the same. Even after our ancestors began spreading out of Africa into parts of Europe and Asia around 2 mya (see Chapter 10), our impact on animals, plants, and the earth itself was negligible. There were too few hominins on the ground, and they could scarcely manage their own lives, much less have a measurable environmental impact on the regions in which they lived. If any part of the human success story can be said to be miraculous, it is simply that hominins did not go extinct during this, our training-wheel period as a biocultural bipedal primate. The archaeological record shows that our Paleolithic ancestors were capable of expanding into new habitats, largely by adapting culturally. Nevertheless, the rate of cultural evolution continued its slow pace throughout the Lower Paleolithic and much of the Middle Paleolithic, while hominin population density remained low everywhere . Things began to get a bit more complicated after about 200,000 ya with the earliest appearance of anatomically and behaviorally modern Homo sapiens in southern Africa . Modern humans began spreading into Asia and Europe after about 150,000 ya. The rate of cultural changes also increased at a faster pace; an Upper Paleolithic hunter-gatherer might have tools, huts, clothing, and even foods that would have been unfamiliar to his or her great-grandparents. Toward the end of the Ice Age, around 12,000– 10,000 ya, Upper Paleolithic huntergatherers differed little in technology and behavior from hunter-gatherer groups that survived into the twentieth century. Throughout the past couple of million years, the lives of hunter-gatherers and their predecessors weren’t easy or disease-free. Our hominin ancestors suffered periodic food shortages that sometimes ended in starvation, and they certainly weren’t strangers to traumatic injury and infectious disease. However, hominin populations up to the beginning of early farming probably did not suffer from epidemic diseases or from such “crowd” infections as the common cold. Because hunter-gatherer populations generally were small and mobile, the reservoir of human hosts for harmful viruses and bacteria wasn’t sufficient to sustain itself in such groups. For most of hominin history, our ancestors’ reproductive capacity also wasn’t much different from that of our ape cousins. A woman who gave birth every three or four years was probably typical of hominins up to just a few thousand years ago. Infant mortality rates were high, as they continued to be after the Ice Age for early farmers (and, regrettably, still are for some communities). Looking back, hominins had a pretty good environmental record up to the end of the Ice Age. According to the archaeological record, it wasn’t because our ancestors were natural conservationists who lived “in harmony with nature.” If anything, it was simply because there weren’t very many of us. What mattered was that we had extraordinary potential as a species: Biocultural evolutionary factors greatly enhanced our chances of biological success and gave us exceptional flexibility in different habitats. By the end of the Ice Age, there may have been 5 million humans (Fig. 16-1), or less than one person for every 10 square miles of land surface. It sounds like very little, but it was sufficient for some human groups to drive local populations of food animals to extinction or nearly so. It also gives us a handy baseline against which to measure some of the events that happened next.
Earliest Farmers and Cities
The end of the last Ice Age marked a watershed moment in which we can find the roots of the so-called Neolithic revolution. Domestication and agriculture were the driving forces of this revolution, but the impact of Neolithic lifeways went far beyond subsistence, and opinions differ as to the effects. The physiologist and popular writer Jared Diamond (1987) bluntly refers to the invention of agriculture as “the worst mistake in the history of the human race.” At the other extreme, Paul Colinvaux (1979), an eminent ecologist, expresses the same glowing perspective as archaeologist Graeme Barker (see p. 349), calling agriculture the “most momentous event in the history of life.” Some researchers argue that human population growth initiated the agricultural response; others see it happening the other way around. But there’s no question that population size and density both tended to increase as farming produced larger and more predictable yields. World population doubled in the 5,000 years after the end of the Ice Age (see Fig. 16-1). In many places, permanent villages and towns sprang up surrounded by fields and pastures. Sedentary living (which in many cases began before agriculture) permitted closer birth spacing, since mothers no longer had to carry infants from camp to camp, and the availability of soft cereal grains for infant food allowed for earlier weaning. Potentially, therefore, a woman might bear more children. And they did. Even very early Neolithic settlements, such as Jericho in the Jordan River valley and Catalhoyuk in Turkey (see Chapter 15), quickly reached considerable size. By a.d. 1, world population had grown to 200,000,000, or roughly 3.5 persons per square mile. As agricultural techniques and resulting harvests improved, surplus production served as a kind of capital, or wealth, that stimulated new kinds of socioeconomic interactions. Some members of society also came to fill specialized roles as priests, merchants, crafters, administrators, and the like. A social and economic hierarchy of productive peasants, nonfarming specialists of many kinds, and a small but dominant elite emerged in a few Neolithic state societies, or civilizations (see Chapter 15). Unlike hunter-gatherers, who extracted their livelihood from available natural resources, Neolithic farmers altered the environment by substituting their own domesticated plants and animals for native species. Neolithic plowing, terracing, cutting of forests, draining of wetlands, and animal grazing contributed to severe soil erosion and the decline of many plant and animal species. Moreover, many of these practices encouraged the growth of weeds and created fresh habitats for crop- damaging insects, malaria-bearing mosquitoes, and other pests. Intensive agriculture also depletes soil nutrients, especially potassium. In the lower Tigris-Euphrates Valley, high levels of soluble salts carried by irrigation waters slowly poisoned the fields once farmed by Ubaidians and Sumerians. In North Africa, Neolithic herders allowed their animals to overgraze the fragile Sahara grasslands, furthering the development of the world’s largest desert. These early farming practices left many areas so damaged that they remained unproductive for thousands of years, until they could begin to be reclaimed with the aid of modern technology. As with other biocultural aspects relating to the development of food production, the effects on human health were a mixed bag of benefits and costs. As farming villages and towns grew larger, infectious disease became prevalent (see Chapter 4). As you know, infectious diseases can cause epidemics, some small, some catastrophic—for example, the Black Death of the Middle Ages or the worldwide influenza epidemic of 1918. They can potentially kill thousands or even millions of people. Huntergatherer populations generally were little affected by infectious disease because they lived in small mobile groups. Farmers weren’t so lucky. One major contributor to heightened disease exposure came from close proximity of humans to domestic animals. Many pathogens—including viruses, bacteria, and intestinal parasites—can be transferred from nonhuman animals to humans. For example, influenza and tuberculosis can be transmitted to humans by contact with some common domesticated animals. Several other significant human diseases are associated with sedentism and increasing population size and density. Measles, for example, has been shown to require a very large population pool—in the thousands—to sustain itself long-term (Cohen, 1989). So, measles became prevalent only with the emergence of larger urban centers, making it a “disease of civilization.” Likewise, cholera is most commonly found in urban contexts, especially where large numbers of people share a common (and contaminated) water source. As if this list of diseases and potential human suffering isn’t enough, bioarchaeological studies have also shown that overall health quality declined with the development of agriculture (Cohen and Armelagos, 1984; Steckel and Rose, 2002). Essentially, our ancestors had traded the uncertain possibility of starvation as a hunter-gatherer for probable malnutrition as a farmer. If it seems paradoxical that average health was declining among food producers at the same time that populations were expanding, that’s because it is. As one researcher commented, “Although humans became physically worse-off in marked respects, they also became more numerous. The agricultural age made possible far denser populations, but less healthy ones than ever before. Historians, anthropologists, and others concerned with this apparent paradox are still exploring its implications in detail” (Curtin, 2002, p. 606). Nevertheless, even with greater exposure to disease pathogens and other health risks associated with living in denser populations, the health picture for early farmers wasn’t all that bleak. After all, it’s ultimately our success as a species (that is, more people) that helped infectious pathogens to be more successful. The advent of farming and the emergence of the earliest civilizations were important components of humankind’s success.
Industrial Revolution to the Present
Story of biocultural evolution with a recounting of the earliest civilizations and the beginning of written history. But by ending the story there, we left a particularly important (and environmentally devastating) part of the human story untold. A graph of world population growth makes the point best . During the past couple of centuries, we humans began to be far more successful as a species than is good for us and the planet. By the year 1800, the Industrial Revolution was well under way, and world population approached 1 billion, or about 18 persons per square mile. Two centuries later, by the year. 2000, we achieved a staggering 105 persons per square mile of every bit of dry land on earth. The current birth rate is such that we now add roughly 10,000 new mouths to feed every hour, 24 hours a day, 7 days a week. Although we chose the Industrial Revolution as our point of departure in this section, no single factor explains the dangerously accelerating growth of world population over the past few hundred years. The growth rate also is not equally distributed among nations. The most recent United Nations report on world population notes that 95 percent of population growth happens in developing countries. Likewise, resources are not distributed equally among all nations. Only a small percentage of the world’s population, located in a few industrialized nations, control and consume most of the world’s resources. A 2009 study estimated that 48 percent of the world’s population exist on less than $2 per day (Population Reference Bureau, 2009). As biologists can tell you, a natural population growth function similar to the one plotted in Figure 16-1 is unsustainable, regardless of whether we’re talking about E. coli bacteria or humans. It is pointless to hope that humans will somehow be the lucky exception to the rule. Dying coral reefs, algal blooms in our lakes, pesticides in our drinking water, air pollution levels that kill the elderly and weak in our cities, rapid melting of the polar ice—all these things are nature’s way of telling us to slow down, control our growth rate, and actively work toward a brighter and more sustainable future for our children (Fig. 16-2). If we can’t or won’t change, then nature can make the point more bluntly (for example, a global pandemic of a deadly disease like Ebola), and common sense tells us that we don’t want to go there. Today, the earth’s human population still relies for food primarily on the seeds of just a half dozen grasses (wheat, barley, oats, rice, millet, maize), several root crops (potatoes, yams, manioc), and a few domesticated fowl and mammals (in addition to fish). Because of their relative genetic similarity, these domesticated species are susceptible to disease, drought, and pests. Agricultural scientists are trying to prevent potential disaster by reestablishing some genetic diversity in these plants and animals through the controlled introduction of heterogeneous (usually “wild”) strains. A few farmers have also rediscovered the benefits of multicropping—interspersing different kinds of crops in a single agricultural plot. Combining grains, root crops, fruit trees, herbs, and plants used for fiber or tools mimics the natural species diversity and reduces soil depletion and insect infestation. The challenge farmers face is to make environmentally friendly approaches like multicropping scalable, such that they are technologically and economically feasible to meet world food demands.
Global Climate Change
At the global level, the biggest environmental problem we currently face concerns climate change, sometimes also called “global warming.” This phenomenon has been researched for more than three decades by thousands of scientists. So, there’s a lot of information out there. Unfortunately, there’s also a good deal of misinformation. Throughout this book, we have emphasized that science is an approach based on data collection, hypothesis testing, generalization, and verification. We have shown that scientific investigation typically can be a long process and one that frequently involves debate regarding alternative approaches and conclusions. It’s important to recognize that science advances as these debates occur in the pages of scientific journals and at organized scientific meetings. Little is gained by uninformed, ideology-driven claims coming from television commentators or from politicians in the heat of partisan disputes. Given all the accumulated scientific data and decades of analysis within the scientific community, there are no major disagreements on two major points: 1. Rapid global climate change has been occurring and continues to occur, including marked warming of the earth’s atmosphere and acidification of the world’s oceans (threatening habitats like the coral reefs that we mentioned earlier). 2. Human activity in the last two centuries is the most significant cause of this climate change. As many of you know, humans have caused these changes as a result of the burning of fossil fuels—that is, coal and petroleum products. This burning leads to about 10 billion tons of carbon dioxide emissions into the atmosphere every year. Along with other “greenhouse gases,” such as methane, these products trap heat in the atmosphere. In turn, the increased heat leads to melting of polar ice, raising of sea levels, and major impacts on weather, including intensification and greater unpredictability regarding droughts, flooding, and hurricanes. What’s more, the vast majority of countries and their leaders recognize that global climate change is a very serious and urgent problem. The United Nations has organized two extraordinary international conferences specifically to take global action. The first of these took place in 1997 in Kyoto, Japan, and as of 2011, its agreements were ratified by 194 countries; the only major country that failed to sign on was the United States. The second conference was held in December 2009 and was attended by representatives of 192 countries, including 60 world leaders. Much anticipation and hopes for building on and strengthening the earlier Kyoto agreements preceded the conference. Unfortunately, and to the collective disappointment of most of the world, even less resulted from this meeting. Another such attempt won’t take place until 2014, at the earliest. Meanwhile, humans pour increasing amounts of greenhouse gases into the atmosphere.
Learning from the Past and Facing an Uncertain Future
Throughout this textbook, we’ve tried to draw your attention to some of the costs and benefits of biocultural evolution, especially those relating to overall human health. As the evidence shows, the rate of cultural changes increased in a manner like that of the world population (see Fig. 16-1), and the effects of increasing cultural changes and population growth are inseparably intertwined. Biologically, however, most humans are still well adapted to being huntergatherers, not suburban, pizza-eating couch potatoes. And in some ways, our bodies haven’t even adjusted to the fact that thousands of years ago, many of our ancestors became farmers. These problems are easier to understand if you view them in the context of biocultural evolution. Some people, even some scientists, claim that the costs of these changes outweigh the benefits. Others feel just as strongly that the opposite is true. Regardless of the perspective you take about the effects of biocultural evolution, whether you see our future as rosy or depressing, there’s no going back. The world we live in is the cumulative product of remarkable contributions made over millions of years by our ancestors who became the first tool users, crossed over into the next valley to see what was there, mastered the use of fire, invented the first composite tools and projectile weapons, domesticated the dog, learned to navigate by the stars, raised the first crop, invented the first printing press, and, yes, even invented the cell phone. Without the benefit of their hard work, sacrifices, and brilliant insights, most of us wouldn’t be here at all. There would be no cities, no art, no educational institutions, no writing, no books—meaning, of course, no textbooks and exams either. And for all the extremely serious damage that can be traced back to our increasing population density over the past few millennia (and particularly over the past couple of centuries), the effects of biocultural evolution, at least in the developed world, also doubled the average modern human life span and brought us affordable mass transportation, high-tech communication and entertainment, and a diverse and easily obtainable assortment of foods, clothing, and shelters. Our challenge, and one that we will bequeath to subsequent generations, is to identify and repair the damage that we’ve caused along the way and to learn how to make things better for all living things and the earth itself.
Summary of Main Topics
▶ By virtue of their biological success, humans have become a major threat to other living things, the earth itself, and even their descendants’ future.
▶ Due to their low population density, slow population growth rate, and limited technology, humans exerted very little environmental impact until the end of the Ice Age.
▶ The world population growth rate and the rate of cultural change both increased slightly with the beginnings of agriculture and the earliest cities and civilizations; measurable environmental impacts resulted, but their effects tended to be only locally felt.
▶ Population growth and cultural changes accelerated greatly since the late 1700s and the beginning of the Industrial Revolution; measurable environmental impacts are now global.
▶ The fossil and archaeological record of the rise of humans shows that our current course is unsustainable. We can change or nature can force the issue. You choose.