Since the Late Pleistocene Humans Were Already Radically Transforming the Earth

A new study suggests that trying to return habitats to a non human-impacted environment might not be realistic

Banaue rice terraces (N. Luzon, Philippines) taken from observation point at beginning of road to Bontoc Wikimedia Commons

“The idea of trying to restore things to a pristine state is not possible,” says Melinda Zeder, senior research scientist and curator of old world archaeology at the Smithsonian's National Museum of Natural History.

“Humans are very much a part of nature,” Zeder says. “The ways in which we modify nature are part of a package of behaviors that we inherited from other species. Look at what beavers do, or what ants do. Manipulating the environment in a way that is favorable. Humans are the ultimate niche constructors.”

These ideas are among the conclusions resulting from years of collaboration between scientists from many different disciplines, culminating in a new research paper of which Zeder is a co-author.

The paper attempts to debunk the common perception that large-scale transformation of wild places by humans began with the industrial revolution. Zeder and her colleagues were part of a team of scientists from various fields who set out to look very closely at how human beings have transformed their habitat throughout history. Their conclusions will shock many people and likely begin a conversation among scientists and policy-makers that will continue for years.

“One of the main points was to press people dealing with modern conservation perspectives to inform them about the deep history,” says Zeder. “What we wanted to do was take the major sort of trends within our discussions and focus on these four major periods that are emblematic.”

According to the paper, those four major periods of habitat transformations by humans include the Late Pleistocene dispersal of humans nearly everywhere around the globe; the spread of agriculture beginning in the Early Holocene; the colonization of the world’s islands; and the expansion of urbanization and trade beginning in the Bronze Age.

One example offered by the paper is the transformation of land into pastures, beginning 7-8 thousand years ago in central and northern Eurasia. Forests and tall grasslands were burned. Introduced species, including the ancestors of modern cattle, thrived on the new growth. The amount of light and heat reflected back towards the sky changed with the switch from forest to to pasture, which seems to have impacted the monsoon system.

In other words, even before the invention of the wheel, humans were already having an impact on global climate change. 

This reevaluation of humans' relationship with nature was made possible in part by new technology and by combining work from different fields of study. “One of the most remarkable achievements in analytical breakthroughs that we've had is the pairing up of archaeological work and ancient DNA,” says Zeder. “A lot of the work that had been done [previously] was just with mitrochondrial DNA, [which can help explain] what was the ancestor of what. But there are labs now that are able to get into the functional DNA, being able to identify the genes being turned on at different points in time.”

According to Torben Rick, director and the museum's curator of North American archaeology (Rick was not involved in the research paper which Zeder co-authored), the paper's conclusions match closely with his own research into human exploitation of shellfish throughout history.

"We've definitely seen those types of impacts," Rick says. "In California, people early on had an influence on the size of shellfish. Lots of examples of where there's people negatively impacting the environment. Even in the Chesapeake, while it was a sustainable system [for the last 11,700 years,] that doesn't mean that they weren't having any impact on it."

One of the biggest issues debated by many scientists today is the idea of the Anthropocene. The word was first used in its current sense in the 1980's to describe the concept of a new geological epoch in which human beings have become the primary influencing factor. The Anthropocene is usually considered as an epoch that directly follows the Holocene. Some scientists place the start of the Anthropocene in the mid-20th century. Others argue for the industrial revolution around the late 18th century. Zeder has a whole other way of looking at it (she was previously co-author of another paper on the subject).

“I think that the Anthropocene and the Holocene are synonymous,” says Zeder. “Humans have been niche-constructing through their entire history.”

Most scientists would agree that the Holocene started roughly 11,700 years ago at the end of the Pleistocene. Many species of megafauna, including mammoths, mastodons and saber-toothed cats became extinct at around that time. Humans were spreading all over the Earth, having already penetrated the Americas, Australia and many islands. Soil biology was changing. Agriculture was emerging in the Fertile Crescent. The glaciers had been in retreat for a few thousand years and a warming trend was under way.

If Zeder and her colleagues are correct in their view that humans were the primary engineers of change on Earth since the late Pleistocene, then maybe there really never was a Holocene. This was the Anthropocene all along.

"I agree with it and then I also say it doesn't matter," Rick says. "There's been so much conversation about when did the Anthropocene start. Did it start 200 years go with the industrial revolution? Did it start in 1945 with [the first test of a nuclear bomb]? To me, the real point is, regardless of when we say the era started, humans have been impacting their environment for tens of thousands of years. ...Let's move past when it started and move ahead to talk about what we're going to do about it. That's what's so important about this paper. If we don't understand the past, the things we did wrong and the things we did that were correct, we can't improve what we're doing."

For thousands of years, humans have been altering landscapes not only through farming and hunting but also through the movement of invasive species. Some were accidental hitchhikers and others were deliberately moved around to provide food and other resources for humans. “In [the islands of] Southeast Asia,” the paper's authors write, “humans transported a range of domesticates, as well as various species of deer, primate, civet, cuscus, wallaby, bird, shrew, rat and lizard to generate habitats more favorable to human sustenance.”

As governments and conservation organizations work to restore habitat, Zeder and the other authors encourage those organizations to look very carefully at exactly what they are restoring that habitat to. The state of an American forest in 1491 or a tundra in 1900 is not necessarily a good point to try to return to. “It is really hard to know what are invasive species and what are indigenous species,” Zeder says. “Some of what we think of as indigenous are yesterday's invasives.”

One of the basic questions that people involved in conservation policy have to ask is a philosophical one: Is humankind a part of nature, or are we actors outside of nature? Zeder sees humans—and our tendency to transform our habitats into something more favorable to our own survival—as a part of nature. But she does not extend that to shrugging at the notion of a species becoming extinct due to human behavior.

“Then do we put ourselves in a position as a god-like creature that decides who stays and who goes?” asks Zeder. “But we aren't god-like in terms of being omniscient and being able to decide what species matters and what doesn't. Where it really becomes pertinent... is the idea that what we are trying to do when we conserve habitats is get back to a pristine environment, a non human-mitigated state. That isn't a realistic approach. What we are trying to define as 'pristine' is human-modified. Having that understanding is a very important concept for management of environments to take into account.”

"There is this myth of something pristine in the recent past or present that we can study and work back towards," says Rick. "That's really a myth that there is anything pristine. We've always been a part of our environment. We've always impacted it. Pristine is not realistic. What's the balance that we want? What environment do we want to restore?"

Most ecologists and archaeologists agree that the ecology of North America was already out of balance before Christopher Columbus first landed on Hispaniola. The reports of early European explorers and naturalists don't represent a sustainable target for conservation. So what should we look at as a target for restoration?

"Ten thousand years ago is a good time to look at," says Torben. "When people were part of the system and we were part of a climatic system similar to today. What we don't want to do is set ourselves up for failure."

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