In 1996, Smithsonian anthropologist Rick Potts , director of the Human Origins Program at the Natural History Museum, turned heads in scientific circles when he proposed that environmental fluctuations were the driving force in human evolution. He spoke with the magazine’s Beth Py-Lieberman.

Conventional wisdom has long posited that African forests became grasslands, prompting our ancestors to climb down from trees, walk upright and use tools. That theory doesn’t work for you? As I delved into the scientific data concerning ancient climate, I began to see fluctuations—between wet and dry, warm and cool—as a very important signal that other researchers seemed to be missing. While everyone else looked at the overall trend to drier grasslands, where we all assumed early humans lived, I started to notice the instability of environments. The fluctuation was perhaps a more important driving force. And then a new idea all started to come together.

Other researchers were focusing on excavating bones and tools, you had a much larger ambition to understand the ancient landscape and the environment. The idea of digging a hole in the ground here or there, and taking everything back to the museum to study wasn’t quite broad enough. So I developed an approach and a research team that began to excavate landscapes. Rather than a single place in the ground to dig, we saw individual layers that we could follow over many square miles. By focusing on these targets of excavation, we could figure out: Where did early humans hang out in that particular environment? Where did they live, and what were they doing? What places did they avoid? The stone tools that they left behind, of course, were the big indicator of their presence on the ancient landscape. That was the first time this approach to excavating had been done.

So, our early ancestors didn’t live only in arid grasslands? For the first four million years of human evolution our ancestors walked upright but also retained very long powerful arms and relatively short legs—which indicates that they were very comfortable climbing in the trees. This suggests that the origin of our ability to walk on two legs was not just an adaptation to grasslands, but rather an adaptation to the tendency of the environment to switch back and forth, between landscapes with many trees and very few. This means that our ability to walk upright was originally part of a very flexible adaptation to environmental fluctuation or instability, not just a single type of habitat.

Is there other evidence for this adaptation? Lots of evidence. For instance, we can now look at stone tools in an entirely different light. A simple sliver of rock is a knife sharper than a carnivore’s canine tooth, while a hammer stone can pound and crush as effectively as an elephant’s molar. The aptitude to create such a diversity of tools suggests an ability to adapt to changing surroundings and eat many different kinds of food. In this way of viewing evolution, stone tool making was not an adaptation to the grassland, but an adaptation to change in the surroundings. This is adaptability – a hallmark of human evolution.

Did you have a Eureka! moment at Olorgesailie, when it suddenly made sense to you? Yeah in a way I did, even though it took many years to have that moment. It came from studying the fossils of other animals besides early humans. The fossil mammals that dominated at Olorgesailie, one layer after another, were forms of zebra, baboons, pigs, and elephants, that were very well adapted to grassland environments. At first, this seemed to indicate that, yes my goodness, the grassland idea of human evolution might well be correct. However, they are the ones that are now extinct, I then realized. And as I traced the fossil record, I wondered which were the zebras and baboons and other animals that survived, and which were the ones that went extinct. It was always the specialized grass-eating forms that went extinct during the last one million years. I sort of hit myself on the head, and said ‘Rick, you’re an anthropologist; maybe this has relevance for humans.’ Our team was figuring out the record of environmental change, and we found that when the grassland species—what I call the large lawnmowers of the Pleistocene—became extinct, they were survived by relatives that were quite able to change from grasslands to tree-dominated environments, and they were the ones that survived until the present.

Describe the kinds of wild climatic fluctuations that were occurring between 700,000 and 150,000 years ago. What was life like for our ancestors? Take this one site, Olorgesailie in Southern Kenya, as an example: What you see is that the lake was sometimes very, very broad. And then sometimes right in the middle of the lake sediments you see evidence of a hard calcium carbonate line, which indicates a drought. And then the lake comes back and is really large again. And then the lake dries up; it contracts. It dries up, and it’s replaced by grassland. And then there are times when it was wetter—more of a woodland and bushy type of environment. So it really fluctuated back and forth, which affected the kinds of food that our ancestors could find. It affected the amount of water that they could secure. It affected the kinds of diseases and the kinds of predators in their environment. And so all of the challenges that would have affected the life and death of these early ancestors of ours, would have been altered, would have been periodically revamped, by these changes in climate, and also by volcanic eruptions and earthquake activity. This led me to think that our basic adaptations, the adaptations that define the emergence of our species and our lineage going way back in time, may have been the result of adaptation to change itself, rather than any single environment.

How does your theory fit with the “survival of the fittest” idea? “Survival of the fittest” means that there is a particular kind of challenge that is consistent over long periods of time. Traditionally, scientists judge an organism as “fit” based upon its ability to survive and reproduce better than other organisms in a specific environment. But you can’t have survival of the fittest when the definition of ‘fittest’ keeps changing, based upon fluctuations in the climate. I prefer to think of human evolution as “survival of the versatile.”

So other hominid species that couldn’t adapt fast enough to new or changing environments died out, until just one, Homo sapiens , remained. Are you saying that climate change is what drove us to become human? That’s a very interesting question. It’s important to realize that even those species that came before us were also adaptable. But what we see in almost all species over the course of earth’s history is that, they’re adaptable only to a certain degree. For example, a close fossil cousin of ours, Paranthropus boisei , had very powerful jaws, and big muscles for chewing food, and walked upright on two legs, had small canine or eye teeth, like we do. It had some of the defining characteristics of a human being. In fact, that particular species lasted for about a million years—five times longer than our species has been around. I think of this species as the eating machine in our family history. With such powerful jaws, it could eat almost anything it wanted to. But there were limits to how long that approach could succeed. In fact, during a time when climate change was ramped up, in East Africa and world environments overall, Paranthropus went extinct. It seems that climate change is not only a driver of evolutionary innovation, of evolutionary adaptations. When it increases beyond a certain degree, climate uncertainty can also be the death knell of species that have been successful for quite a long time. It’s a matter of how you trim the branches of our evolutionary tree so that earlier species that were close cousins of ours ultimately became extinct after a successful run. When you look at the record of earth’s climate, instability is the big driver of adaptability and extinction.

How will versatility benefit humanity as it confronts global climate change? The rate of global climate change poses a serious challenge today. I’m especially concerned about the element of instability, which causes uncertainty about precisely how we should respond.

Our ability to modify our immediate surroundings owes a great deal to our heritage of adaptation to climate change. The ability to make a simple hearth, to build a shelter, or to plant a seed and tend it and watch it grow, are all ways of controlling our surroundings that improved our ancestors’ ability to survive in the face of uncertainty. Well, these approaches became so successful that our species has spread all over the globe. And once you take all these reasonable approaches to altering the local environment and you make them worldwide, that’s global change. In the modern world, this results in huge numbers of people all crowded together; and a huge ability to pollute the environment because humans generate a lot of waste. We’ve become dependent upon a few animal species and a few plant species to feed us. So the changes we make in the landscape, the air, the water, all tug upon the strings that caused environmental instability in the past. Much of the discussion today is focused on how will we adapt to a particular climate trend, global warming, for example. My concern about this new experiment is not only about the trend but also about instability. Instability causes the uncertainty. Should we respond to climate warming in this particular way, or that particular way? Sometimes right in the middle of climate warming, you actually find a small blip of cooling – part of the natural fluctuation. But that then messes with our perception: ‘well, maybe it’s cooling, not warming?’

But I’m actually quite optimistic about our future. By virtue of our evolutionary history, we have amazing social abilities—ability to help one another, ability to innovate technologically and the ability to change our minds and to build new understandings of the world. Those traits have never existed in any other organism, including our early ancestors.

From the Castle: Becoming Us

Why do our wisdom teeth often cause problems, and why do we have relatively hairless skin? The answers come from our distant past. Anyone with Internet access will soon be able to solve such mysteries in the Smithsonian’s compelling Web site, “Human Origins: What Does It Mean to Be Human?” ( humanorigins.sidu ). The National Museum of Natural History’s new David H. Koch Hall of Human Origins, opening March 17, marks a milestone in the Institution’s long involvement with the study of early humans. Field research, 3-D and other digital images available to all on the Web site, educational and public programs will complement the new $20.7 million hall, which tells the epic story of how a single human species emerged over time and spread worldwide. Less well known is that during most of this journey, two or more species of early humans existed simultaneously. After several million years, one lin­eage led! (See “ Our Earliest Ancestors .”)

The 15,000-square-foot hall focuses on the ways defining characteristics of the human species developed as our ancestors adapted to a changing environment. A time tunnel introduces earlier human species. Visitors learn about major changes in climate and other key events in humanity’s evolution. And they look into the eyes of distant ancestors in forensically reconstructed life-size faces. More than 75 skull reproductions, a human family tree and virtual tours of key research sites illuminate our ancestors’ increasing brain size, technological expertise and artistic creativity. Lead curator Rick Potts says the hall will help define humanity’s “cultural and biological characteristics and how those traits emerged during one of earth’s most dramatic eras of environmental change.” Potts’ book, What Does It Mean to Be Human? , published in conjunction with the new hall, details the evidence for human evolution and for connecting the emergence of human traits to changes in climate over millions of years.

Our Human Origins initiative exemplifies the Smithsonian’s growing resources for teachers, students and lifelong learners. As Carolyn Gecan, a teacher in Fairfax County, Virginia, says: “I can now send my students on virtual field trips to Olorgesailie, Rick Potts’ field site in Kenya.” The initiative also demonstrates how our Web sites extend our reach hundreds-fold as we take our cutting-edge research, vast collections, exciting new exhibits and behind-the-scenes activities worldwide—inspiring wonder, encouraging curiosity and delivering knowledge, including explanations of why our wisdom teeth frequently cause trouble and why we aren’t covered in fur. (Our ancestors had larger jaws so they could chew tough food. With the development of tools and cooking, our food became easier to chew—and our jaws got smaller, often unable to accommodate wisdom teeth. Bare skin helps dissipate heat; in the places early humans evolved, overheating was more of a problem than being too cold.)

G. Wayne Clough is Secretary of the Smithsonian Institution

Drawn From Life

When Janice Lowry turned 11, inspired by reading The Diary of Anne Frank , she began keeping a journal. Not unusual for a young girl. What's unusual is that throughout her life, Lowry—who died of liver cancer this past September at age 63—kept up her diaries.

From childhood on, Lowry filled small notebooks with daily musings and drawings. Then, in the mid-1970s, she moved to a larger format, 7 1/2- by 9 1/2-inch notebooks. For almost 40 years, Lowry—an artist best known for her intricate, three-foot-tall assemblages—filled the roomier notebooks with jottings and sketches. The pages contain everything from original drawings, collages and rubber-stamp images to observations about herself and the world, including the commonplace "to-do" lists many of us make: "pay bills/make plane res/get asthma med/Judi birthday gift."

Each notebook spans about four months, transcending minutiae to record the life of our times as well as her own. Entries touch on events from a child's birthday to the contested presidential election of 2000 and the anniversary of the September 11 attacks. This past July, the Smithsonian Archives of American Art acquired all 126 volumes.

Artists' journals can be an art form unto themselves, a taxonomy of days that attempt to capture the random rush of creativity. Free of formal constraints (beyond the size of the page), artists can use anything that comes to mind, eye or hand. "I call these books 'reportage,'" Lowry said in an August interview. "There are certain themes that run through the journals consistently—health, motherhood, political things, being an artist, even fashion and television. Originally, I saw them as books for my sons, so they could see my progress through life. Now they're 126 chapters of a memoir."

Lowry was an art student raising two young sons when she switched to the large-format journals in 1974. "At the time, I didn't have any role models to help me figure out how to do these journals," she recalled. "When I had a vision of something, I could just do it."

In 2006, Patricia House, then director of the Muckenthaler Cultural Center in Fullerton, California, visited Lowry's Santa Ana studio because she intended to include Lowry's assemblages in an upcoming gallery show.

There, House first saw the neatly stacked diaries; she instantly recognized their value and informed Lowry that the collection needed a "steward."

"I've seen a lot of artistic diaries, but these were different," says House. "I saw works of art."

Lowry took her colleague's advice. She put together seven of what she called "packets"—illustrated introductions to the journals—and submitted them to research centers and museums around the country. Liza Kirwin, who is curator of manuscripts at the Archives of American Art, received one of them.

"The packet was very inventive," Kirwin recalls, "with a handmade envelope and very curious contents. It was such a creative expression of an artist's life. About 20 seconds after looking at it, I sent an e-mail message [to Lowry] saying that the Smithsonian should have the journals."

Shortly after, Kirwin says, the artist sent two complete journals to the Archives. "We used them right away for an exhibition of sketchbooks," Kirwin remembers, thereby allowing Lowry to cross off a very important item on one of her last to-do lists: "Find steward for journals."

Owen Edwards is a freelance writer and author of the book Elegant Solutions .

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