Human History and the Biosphere

Human History and the Biosphere

Lecture 45

In the 20th century it became apparent for the rst time that humans were beginning to have a huge and perhaps disruptive impact on many aspects of the biosphere.

In the previous lecture we tried to stand back and survey the major structural changes of the Modern era. However, we deliberately skipped one large group of changes: changes in our relationship with the biosphere. These have a direct bearing on the question of sustainability. To see these changes clearly we must widen the lens further to include all of human history.

In the 20th century, it became apparent that humans were beginning to have a huge and disruptive impact on many aspects of the biosphere. The term “biosphere” was invented by Austrian geologist Eduard Suess (1831–1914) and popularized in the 1920s by Russian biologist V. I. Vernadsky (1863–1945). It refers to the region of Earth, water, air, and living organisms at the Earth’s surface that sustains life on this planet.

The major turning points in human history are all associated with humans’ increasing control, or new forms of control, over the resources of the biosphere. This is what we generally mean by “growth.” But setting human history in the context of the biosphere reminds us that this was really a grab for resources by a single species: our own. By the late 20th century, it was apparent that our increasing ecological power was affecting the biosphere as a whole. John McNeill argues (in Something New Under the Sun) that our changing relationship to the environment may have been the most important change in the 20th century. To understand these changes, we must review our relationship with the biosphere over the 250,000 years of human history.

What impact did Paleolithic humans have on their environment? The rst distinguishing feature of our species was a greatly enhanced ability to adapt through collective learning. Adaptation itself implies an increased capacity

to manipulate our surroundings, so collective learning necessarily implies an increasing impact on the environment.

In the Paleolithic era, the impact of this constant exploration of the environment was limited. As “foragers,” Paleolithic humans consumed natural products largely in their natural form. Populations were small and communities were scattered, so their ecological “footprint” was small.

Yet even in the Paleolithic era, the environmental impact of our species was remarkable. Our Paleolithic ancestors learned how to exploit natural environments throughout the world. As they did so, they developed new techniques for dealing with different environments, from the tropics to the tundra. Each new migration was a signi cant technological achievement. Some of the techniques developed in the Paleolithic era had a signi cant environmental impact. Foragers throughout the world red the land regularly to increase plant growth and attract prey species. Over thousands of years, such practices could change the mix of plants and animals over entire continents. As their hunting techniques improved, our ancestors may also have helped drive many large mammal species to extinction, particularly in newly colonized lands such as Australia and the Americas, where local fauna had no experience of dealing with humans. Evidence on the “megafaunal” extinctions remains ambiguous, but the fact that these extinctions appear to coincide roughly with the arrival of humans makes it likely that humans played a signi cant role.

In the Agrarian era, humans began to transform their environments more systematically. Agriculture requires systematic, large-scale manipulation of the natural environment. Farmers transform environments so as to discourage species they don’t need (which they call “weeds” or “pests” or “rodents”) and encourage species they do need (which they call “domesticates”). This may mean plowing (removing weeds and exposing fertile sub-soils) or the deliberate elimination of pests such as wolves. It may require more elaborate changes such as diverting entire rivers into arti cial channels to water crops in arid regions. Used badly, such methods could ruin the fertility of soils over large areas, as seems to have happened in Sumer 4,000 years ago. Swidden agriculture led to widespread deforestation. Farmers also manipulated species of plants and animals through domestication, turning

wild plants and animals into “domesticated” species that were more useful to humans and were therefore encouraged to multiply rapidly. In towns and cities, humans created entirely anthropogenic environments. There was little that was not shaped by the presence of humans in even the oldest cities, such as Ur. Increasing control over environmental resources allowed humans to multiply from about 6 million people 10,000 years The rst distinguishing ago to more than 250 million people just 1,000 years ago. feature of our

species was a greatly

The Modern Revolution has vastly increased enhanced ability human impacts on the biosphere. Each of the to adapt through more than 6 billion humans on Earth today consumes approximately 60 times as much collective learning. as energy as humans of the Paleolithic era. These gures suggest that the total energy consumption of our species has increased by about 60,000 times in 10,000 years. Most of this astonishing increase arises from population increase and the introduction of fossil fuels during the Modern Revolution. John McNeill estimates that in the 20th century humans became the most important movers of earth, more important even than natural erosion. Mining had the greatest impact on soil movements. As humans consume more resources, fewer are available for other species. So rates of extinction have accelerated sharply in the Modern era. Indeed, current rates of extinction may be similar to those of the ve or six most spectacular extinction events in the last 600 million years. In the 20th century, humans engaged in a vicious and prolonged war with the bacterial world after the introduction of antibiotics. The outcome of this con ict remains uncertain as bacteria develop new and more resistant strains. Finally, massive consumption of fossil fuels is increasing the levels of carbon dioxide in the atmosphere, while other activities, including cattle farming, are raising the levels of other greenhouse gases such as methane. The result is that we are beginning to alter global climate patterns. Though there is debate about many aspects of global warming, there is no doubt that the level of carbon dioxide in the atmosphere has increased signi cantly since the Industrial Revolution. Will global warming cause changes as drastic as

those of the last ice age—but in the opposite direction? We may nd the answer to such questions within our lifetimes.

In summary, evidence is accumulating that we are now using more resources than the biosphere can provide, with the risk of a serious breakdown. We have seen such breakdowns before, but this time it threatens to be global rather than local. Such conclusions suggest the folly of treating human history as separate from the history of the Earth. Human history has evolved within the complex global lm of life that James Lovelock has called “Gaia.” Lovelock has argued, controversially, that the entire biosphere constitutes a single feedback system that has maintained the surface of the Earth in a state suitable for life. This is a view of evolution in which cooperation seems more important than competition. Yet Lovelock argues that human activity may now be threatening the stability of the global “Gaian” system.

We have seen that in the course of human history, humans have used more and more resources at an accelerating rate. Is this a story of triumph, or a sign of danger? Where is all this going? In the last three lectures of the course we will try to answer this question by peering into the future.

Essential Reading

Supplementary Reading

Christian, Maps of Time, chap. 14. McNeill, Something New Under the Sun.

Hughes, An Environmental History of the World. Turner et al., The Earth as Transformed by Human Action.

Questions to Consider

1. Why has our species had such an extraordinary impact on the biosphere?

2. How can we assess when human impacts on the biosphere become dangerous both for the biosphere and for our own species?