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What's the Use of "Big History?"

David Christian

San Diego State University

Editors' Note: This presentation was originally given at the World History AP exam reading in Lincoln, Nebraska, in June 2005. David Christian has generously allowed World History Connected to reproduce the presentation, along with PowerPoints, in this issue.  


PowerPoint Slide 1



    It's an honor to speak to a gathering that includes many of the best world history teachers in the country! So I am extremely grateful to the organizers for inviting me. 1
    In this talk, I'd like to explore a very simple idea: that there is a lot to be learnt by looking at history on very large scales, even on scales larger than those of World History. Specifically, I'll offer some reasons why it is illuminating to explore the past on the very large scales of what is coming to be known as "Big History."


PowerPoint Slide 2



1) First of all, I'll talk about what big history is and how it began. Briefly, big history surveys the past on all possible scales, beginning with the origins of the Universe and ending now. In a thirteen week semester this has the wonderful consequence that we cover, on average, a billion years each week!
2) Second, I'll ask what use it is to look at the past on scales much larger than those familiar to most historians. I'll argue that the reasons for doing big history are similar to the reasons for doing world history, except on even larger scales. Like traveling away from home, big history helps us see familiar aspects of the past in unfamiliar ways. World history can do this for nationalist history (histories of particular nation states); big history can do the same thing for world history. 4
3) Third, I'll give some illustrations of my main claim: that the very large scales of big history can help us see familiar things in new ways. I'll argue that it can offer new perspectives on the past, suggest new and illuminating comparisons, and provide new ways of clarifying the essential nature of world history.
4) Finally, I'll return to the scales of world history and ask how the big history perspective may change our view of the central themes and turning points of world history. I'll list some of the themes that seem to me to stand out most clearly when we look at world history within the large scales of big history, and I'll list what seem to me the crucial turning points in world history. I'll end by offering some uninvited suggestions about the AP World History syllabus that arise out of this discussion. 6

Definitions? Just as world history tries to look at the past on scales larger than those of the nation state or the particular civilization, so big history tries to look at the past on even bigger scales, up to the largest scales of all, those of cosmology. Big history tries to look at the past on all scales, from those of conventional history up to those of cosmology. 7
Origins. Something like big history has been taught in most societies. So in a sense, big history is a very old way of teaching history. But it vanished from professional historical research and teaching in the 19th century and only now seems to be making a bit of a comeback. Here I will talk only about the origins of my historian's version of the "big story".  
    I began teaching big history at Macquarie University in Australia in 1989. By coincidence, John Mears began teaching a big history course at Southern Methodist University in Dallas at about the same time. In 1991, I published in the Journal of World History a description of my big history course, called "The Case for 'Big History'". That's when I coined the term, "big history", so this provides me with an opportunity to make amends. Yes, it's over-blown, strident, and pretentious; but . . . it's stuck and so I'll stay with it. In 1996, Fred Spier published the first book on big history, The Structure of Big History, and in 2004, I published the first book-length survey of big history, Maps of Time: An Introduction to Big History. Meanwhile, several courses in big history have appeared in Australia, the US and the Netherlands, and now, also in Russia. And there are similar courses also within other disciplines, such as astronomy, geology and ecology. [For more on other big history courses, see Fred Spier's web site on big history, at: .] 8
    My course in big history began with the origins of the Universe and ended now. Why would I have done such a thing? That's what I asked myself as I prepared to teach the course for the first time. The project had begun bravely two years before when I had what I thought was a really cute idea about our first year course in history. Instead of arguing endlessly about what we should teach our introductory students, I thought why not start at the beginning, as they do in so many other disciplines? I soon figured out that that meant starting with the big bang, as I couldn't find any earlier stopping point that made much sense. So I recruited a team of lecturers in astronomy, biology, geology, anthropology, ancient history and so on. I was very nervous before the first lecture. If the course bombed it would have been very bad for the students, bad for the department but, above all, very very bad for me. We got through the first lecture (on creation myths). The second lecture was on the big bang, in other words on the origins of everything. The astronomer who was to give it (the late David Allen of the Anglo-Australian observatory) didn't make me any more comfortable by phoning to apologize that he had been swamped with work and had not managed to prepare much, though he assured me everything would be fine on the day. When he turned up to give his lecture, he didn't have a scrap of paper with him, no notes, no slides, nothing. I tried to sit him down with a cup of coffee in the hope that he would jot something down, but he asked to be shown around the campus. I was not in a good state by the time he started his lecture, in a quiet undramatic voice. Then something astonishing happened. I suddenly realized that I and everyone else in the theatre had become so absorbed in the wonderful story of the big bang, that we had completely forgotten where we were. Though there were over 200 people in the room, you could have heard a butterfly. It was a wonderful lecture, and at that point I believed for the first time that this might work. 9
Student Reactions? From the beginning the course attracted large numbers of students. It was and still is the largest course in the modern history department at Macquarie University, and that made me invulnerable, for reasons that anyone who has worked in a history department will understand. Despite its difficulties, each year there was a significant cadre of students who found it intellectually exciting because of its sweep, its scale, and its attempt to embrace all origins. Not all students enjoyed the course (I remember one complaining: "Why do I have to do this boring stuff about the origins of the Universe; why can't I just do World War I"). But enough found it really exhilarating for the course to be pronounced a modest success. I began to teach it annually, which gave me the chance to do some fine tuning. Over time, I gave more and more of the lectures myself, which made the course more coherent, if less expert. 10
My own reactions? As for me, I had fun! Teaching big history is as close as I'll ever get to riding a motor bike very fast on a narrow cliff-side road. It was a rush. (Which is why I was delighted when one review of Maps of Time described it as "tailor-made for historians who enjoy an intellectual rush." [Nick Doumanis, "History Writ Large", Australian Journal of Politics and History: Volume 51, Number 1, 2005, pp. 114-124, from p. 123.]) We taught the course in a 13 week semester, and I used to appall my historian friends by confessing that we were traveling at an average speed of one billion years a week! They were even more appalled when they found out that humans did not appear in the course until the 4th week. 11
My syllabus in big history: The structure that evolved by the mid 1990s is still essentially the shape of the course I teach today. We began by explaining what big history is, and introducing the idea that it can be thought of as a modern creation story, a modern story of origins. Then, in lectures and discussion groups, we discussed the big bang, the creation of galaxies and stars, the creation of our solar system, the early earth and the history of the earth and atmosphere, the origins of life and the major turning points in the evolution of life on earth. In about the 5th week, we discussed the evolution of our own species. Generally at that point we inserted a lecture on the differences between history and science, and the nature of truth itself, before going on. (The question underlying that lecture was: how can we know whether or not to trust a particular creation story?) We discussed the Paleolithic era, the origins of agriculture, the emergence of the first cities and states, the evolution of agrarian civilizations, and eventually the emergence of the modern, industrial world. After a few years, I realized the story generated so much momentum that it was crazy not to talk about the future. So, for several years, I and the biology lecturer, David Briscoe, used to do a double lecture in which one of us argued for a bleak future and the other for a utopian future. 12
What use is it? Before I answer that question, I want to put the same question to world history. 13

    Turning to my trusty AP World history course description, I find on p. 7 the following description of the distinctive "Habits of Mind" addressed by world history: 14


PowerPoint Slide 3



1) "Seeing global patterns over time and space while also acquiring the ability to connect local developments to global ones and to move through levels of generalizations from the global to the particular"

2) "Developing the ability to compare within and among societies, including comparing societies' reactions to global processes"

3) "Developing the ability to assess claims of universal standards yet remaining aware of human commonalities and differences; putting culturally diverse ideas and values in historical context, not suspending judgment but developing understanding"



PowerPoint Slide 4


    It seems to me that these three habits of mind can be described under three main headings: Perspective; Comparisons; and Framing. Let me explain what I mean by these headings. 15
1) Perspective: By perspective, I mean learning about something by seeing it in its context. This means seeing the larger community or entity of which it is a part. By placing something in perspective, you learn that it does not exist by itself, but is integrated in various ways in to other, larger entities. Perspective can give a sense of realism. It can help American students learn that the USA is part of a wider world and the future of the USA is inextricably bound up in various ways with the future of that wider world. They can also learn the extent to which their own society is made up of immigrants from that wider world so that its culture is woven from many strands, most of which come from elsewhere. 16
2) Comparisons: Comparisons mean that you learn about something by comparing it with other things with which it has some similarities. American students, for example, can learn a lot by learning about the very different histories of Africa, and asking what makes the US different from Africa, as well as what makes it similar? 17
3) Framing: Finally, by seeing something in context, and comparing it with other things with which it shares some similarities, you can get a clearer idea of what really is different about the thing you are studying. You can only really understand what is unique about the USA if you have had a chance to compare it with other countries. 18
Traveling in time: Put more simply, the best way to learn about your own society is to travel to other societies and look at your own society from outside. This is why travel itself is such a wonderful learning experience. As History teachers, we help our students travel in time and space, and by doing that we help them learn more about the society of which they are a part. We learn by moving away from the object we're studying, then coming back to it and seeing it through more traveled eyes. 19

    Do the same principles apply when we move beyond the conventional scales of world history? I will argue that they do, and that big history can therefore do for world history what world history can do for nationalist history: it can help us see familiar things in unfamiliar ways. 20
    I'll illustrate how it can do this under the three headings of perspective, comparisons and framing. 21
PERSPECTIVE: If world history shows how our nation fits into the world as a whole, can big history show how human history fits into the Universe as a whole? 22


PowerPoint Slides 5 - 7


A Sense of Perspective: Is there any point in looking at human history from scales larger than those of the world? The first hint that there may be something to learn comes from the wonderful photographs of the earth from space that appeared in the 1960s as the first humans traveled in space. Astronauts and cosmonauts were uniformly moved by those pictures, as were many other people. What they did was to show that our world is very beautiful, but also rather isolated and fragile. They also created a vivid sense of the earth as our common home, and one that we share with many other species. Kevin Kelley's wonderful Our Home Planet combines photographs from space with interviews from astronauts. 23


PowerPoint Slides 8 - 11


    But if you travel even further away, the sense of isolation and loneliness intensifies, and the perspective begins to change. Eventually, humans, our planet and our history get completely lost. Here is a perspective that suggests the total insignificance of humanity and our history. It is realistic, I suppose, though many also find it depressing. However, some may find awe in the sheer scale and richness of the Universe of which we are a tiny part. 24
    Something similar happens if we look at the Universe chronologically. The easiest way to get a sense of how brief human history is in comparison with the history of the Universe is to imagine that the 13.7 billion years since the Big Bang were to be collapsed into a mere 13 years. How would human history fit into that scale? 25


PowerPoint Slide 12



Fundamental Dates: Here are some of the fundamental dates. If we imagine that the Universe was created just 13.7 years ago (instead of 13.7 billion years ago), then:

The earth was created 5 years ago

The first multi-celled organisms appeared about 7 months ago

The asteroid that wiped out the dinosaurs struck about 3 weeks ago (a crucial event; if it had been slightly faster or slower it would have missed us and the dinosaurs would still be roaming the earth)

The first hominids (bipedal apes) would have appeared about 3 days ago

The first H. Sapiens, about 53 minutes ago

Agriculture about 5 minutes ago

The first civilizations about 3 minutes ago

The Industrial Revolution about 6 seconds ago

Clearly, human beings and human history can seem totally insignificant in both the spatial and temporal scales of modern cosmology.



PowerPoint Slide 13


The place of humanity in other cosmologies: It's worth noting that this perspective is different from that of most pre-modern ways of looking at our place in the universe. For example, the Ptolemaic model of the universe, which dominated thought in medieval Europe put the earth at the centre of the universe, and put humans at the centre of the earth. In this cosmology there could be no doubting the importance of humans. 27
    In short, big history can help us see world history in cosmological perspective.  
COMPARISONS: If world history can suggest useful comparisons and contrasts between national histories and those of other societies, can big history suggest interesting comparisons and contrasts between human history and other histories? 28
    I think it can, and I will illustrate this claim by taking up the theme of complexity. Human history is complex. We all know that. That's why the discipline is so fiendishly hard, and it's why historians, unlike physicists, have not been able to come up with neat general laws. Furthermore, it seems that human history has got more complex in the course of time. Can we learn more about such processes by comparing human society with other complex things? 29
    The default state of the universe seems to be one of extreme simplicity. If you picked a random spot in the universe and grabbed a handful of stuff, the odds are overwhelming that you would be grabbing an extremely cold bit of emptiness. This is what most of the Universe is like. Still, in some spots, more complex things have appeared. But it is never easy creating such things. Creating complex things means going against the grain of the Universe as a whole, which is why it is always hard work. This means that it requires a flow of energy, whereas creating very simple things does not. As Stuart Kauffman puts it: "the maintenance of order requires that some form of work be done on the system. In the absence of work, order disappears." [At Home in the Universe, pp. 9-10] 30
    The fact that making complex things requires a flow of energy suggests that, even if we're not sure what complexity is, perhaps we can rank different things by their degree of complexity. This is what the astronomer, Eric Chaisson, has suggested in his book, Cosmic Evolution. His idea is that the more complex an entity is, the greater the energy flows that ought to be needed to maintain it. So energy flows provide a rough way of ranking entities by their level of complexity. Here are his calculations. 31

    The unit he uses describes the amount of energy (in ergs) that flows through a given mass (in grams) in a given time (in seconds). Using this unit, and some back-of-the-envelope calculations, he concludes that, the "free energy rate density" (the flow of energy) of different entities is as follows [Cosmic Evolution, p. 139]:

  • A galaxy (the Milky Way):
  •   0.5   [ergs/gr/sec]
  • Stars (the Sun):
  •   2    
  • Planets (the surface of the Earth):
  •   75    
  • Plants (biosphere):
  •   900    
  • Animals (human body):
  •   20,000    
  • Brains (human cranium):
  •   150,000    
  • Society (modern culture):
  •   500,000    


    PowerPoint Slide 14


        These figures may be surprising. Clearly, there is more energy flowing through the sun than through the surface of the earth. Nevertheless, the mass of the sun is so much greater than the mass of the earth's surface regions that this more than compensates, so that the density of energy flows at the earth's surface turns out to be greater than the density of energy flows for the sun as a whole. 33
    Human societies are extraordinarily complex: If these calculations mean what Chaisson thinks they mean, they provide a way of measuring how complex human societies really are. And what they suggest is that modern human societies are extraordinarily complex. 34


    PowerPoint Slides 15 - 20


    Increasing complexity and control of energy in human history. In fact, we can see the build up of that complexity in the course of human history, by looking at how humans have increased their capacity to control energy flows at the surface of the earth. Indeed, the ways humans have done this must surely count as one of the dominant shaping forces in world history. While Paleolithic societies seem to have mobilized about 5,000 Calories per person per day, early agrarian societies probably mobilized about 12 C., more advanced agricultural societies mobilized about 26 C., early industrial societies about 77 C., and modern industrial societies can mobilize about 230 C. As human populations have multiplied by at least 1,000 times in the last 10,000 years, this means that the total amount of energy mobilized by our species as a whole has increased by a factor of almost 50,000 times. 35
        Increasing control of energy shows up in the very earliest phases of human history, in the migrations that allowed humans to settle all parts of the world by learning how to extract energy and resources from many different types of environment. Eventually, increasing control of energy allowed human populations to increase, and as they increased their interrelations became more complex. This was particularly apparent when humans first began to practice agriculture from about 10,000 years ago. This sudden increase in the ability of humans to divert energy to their own uses led to accelerated population growth, which eventually led to the appearance of the larger concentrations of humans we describe as cities. Within cities, social relations became vastly more complex than they had been in the smaller and simpler societies of the Paleolithic era. Then, in the modern era, there was another sharp acceleration in human control of energy. This was associated with what is often called the "Fossil Fuels Revolution". By some estimates, humans now control between 25% and 40% of all the energy that enters the biosphere through photosynthesis. Clearly, if one species controls this much energy, other species may feel the pinch. And indeed they do. Extinction rates of other species are currently as high as they have been during the 5 or 6 periods of most rapid extinctions during the last billion years. 36
    How complex is modern human society? Seen in this way, modern human society, the thing that most historians study, begins to look much more interesting. It begins to look like one of the most complex things in our universe. There's an interesting line of argument, linked to the physicist, Enrico Fermi, that suggests that we may be uniquely complex, even perhaps on cosmological scales. His argument was that if creating societies such as ours was easy, then there ought to be lots of these societies around, and we ought to have picked up traces of them, because some must have existed for millions of years and must have had technologies much more advanced than ours which would allow them to send signals and objects into space. At our (presumably relatively puny) level of technological power, we are already sending signals and objects into space. (The first human made object to leave the solar system, Voyage 1, crossed the border, according to some estimates, in December 2004.) So there ought to be a lot of electronic and physical junk out there. But in thirty years of looking we haven't yet detected any. To Fermi, and to many others, the absence of any clear evidence for the existence of other species capable of generating civilizations like ours suggested that we may be unique within the galaxy as a whole, and perhaps even on the scale of the universe. 37
    Back to the centre of the Universe? If these arguments are valid (and I should stress that they are rather speculative, but we know of no better arguments), this suggests that perhaps modern human society counts as the most complex thing that this universe can create! That puts humans back near the centre of the universe, where they were in Ptolemy's universe. 38


    PowerPoint Slide 21


    But complexity is not necessarily good! But this is not quite the end of this line of argument. Magnificent we may be, but we're also fragile. Complexity is not necessarily good! Chaisson's original table has a column that I removed the first time around. It estimates the life-expectancy of different entities at different levels of complexity. And the pay-off is pretty clear. As one would expect, the more complex a thing is, the harder it is to make, the rarer it is and the shorter its normal life span. Neither we as individuals, nor the astonishingly complex societies we belong to will last as long as much simpler entities such as the earth or the sun. Complexity is not necessarily good or progressive. It's just . . . complexity. 39
        I hope it is clear that these comparisons help us to see human history in rather new and rather powerful ways. They suggest that the material that historians study is close to the maximum of complexity possible, so it should be no surprise if historians have failed to come up with simplistic rules to explain human history. 40
        In summary, comparisons with the histories of other entities help us understand both what human history shares with other histories (in this case, the use of energy to build complexity), and what makes it different.  

        Finally, framing. If world history can help us get a clearer sense of what is distinctive about particular regional or national histories, can big history do the same for world history? Can it give us a clearer sense of what world history is really about? I think it can. 41
    What makes humans different? Let's go back to the argument I've just presented about the complexity of modern human society. Why is modern human society so extraordinarily complex? What makes our species so different? Why have we been able devise such complex technologies and create such complex societies? 42
    Mobilizing energy flows: Here's a possible answer. We've seen that complex things can exist only if they can tap into large flows of energy. They must organize themselves in such a way as to do this otherwise they cannot exist. So the question is: why are humans so good at mobilizing these huge energy flows? And why have they got better and better at doing so in the course of human history? All animals need energy and resources to sustain their complex structures. But why is this organism so good at the job, and apparently getting better and better at it? Somehow, it's as if we have found a new and much faster way of adapting to our environments. 43
    Three ways of adapting to the environment: Adaptation may be the key to this puzzle. All living things learn how to extract energy from their surroundings in order to survive. But over time, new species appear that have found new ways of extracting energy so they can flourish and reproduce. We can distinguish three main ways of adapting. 44
    1) The first is natural selection. Any organism that has a slight advantage in controlling energy and resources is more likely to survive than other members of its species. Its offspring are also likely to share these advantages because the genetic mechanisms based on DNA will faithfully record the advantageous changes and pass them on. And in this way, over 4 billion years, all the variety of our planet has been created. But this method is slow and wasteful. Each experiment uses up an entire life, and new ways of controlling energy appear very occasionally, through a random process of trial and error. 45
    2) But there's a second, much faster, way of adapting, by learning. Animals with brains can change their behavior within their lifetimes. This method of change is much more rapid, but unfortunately there's no equivalent of genes to transmit it to later generations. That's why learning is rather unimportant at large scales. It's not cumulative, like genetic change. Each individual has to start learning from scratch. 46
    3) What humans have done is to stumble on a third way of adapting that combines the precise storage mechanisms of genetic change with the speed of learning. I call this new mechanism "collective learning". Because of the precision and open-endedness of human language, humans can share what they learn in great detail, so that the learning of individuals gets stored in the culture of the community. Because each individual can add something to that store of knowledge, human knowledge of how to adapt can accumulate from generation to generation. This method of adapting combines the advantages of learning (its speed) and natural selection (faithful recording of successful experiments). This is by far the most powerful adaptive mechanism on the planet, and perhaps (if Fermi's argument is correct) in the galaxy. 47
    A definition of our species? If I'm right, the idea of collective learning provides a simple way of defining what makes us unique and therefore what makes history unique. Whereas change in the biological realm is shaped by natural selection, change in the human realm is shaped by collective learning. This is what makes us different. And this is what explains the distinctive features of the history discipline. Historians deal with the only species on earth that adapts using the unique mechanism of collective learning, a constant process of sharing information through social networks that extend over large areas and accumulate information from generation to generation (with occasional setbacks). 48
        I hope this suggests the power of large scales to help frame and define the central object of our enquiry as historians. 49



    PowerPoint Slide 22


        Now I'd like to return to world history with one simple question: returning after this journey to other temporal and spatial scales, what aspects of world history stand out most clearly? 50
        I think three main themes stand out. (Not entirely coincidentally, these are similar to the three central questions [Humans and other Humans, Humans and Ideas, and Humans and the Environment] used in the world history syllabus that I helped work on as part of a team organized by Ross Dunn: World History for us All. The web site for this syllabus is available at: 51

    Three linked themes for World History:

    1) Social Complexity: The first theme concerns the extreme complexity of human history and modern human society. This conclusion won't surprise a historian, but the arguments presented above may help suggest how we can put that conclusion on a firm, scholarly foundation, rather than relying on our intuition as historians. We have seen that there are objective ways of measuring complexity, and that modern societies exist at an extraordinarily high level of complexity. No wonder human history is so diverse, so varied, so unpredictable, so quirky. Of course, we need to insist that extreme complexity is not necessarily good or bad; it's just the way things are. But it is astonishing and apparently unique to our species.

    2) Intellectual Networks: Second, though, our foray into big history suggests that extreme complexity is closely linked to our intellectual and cultural history in profound ways. Collective learning, I have argued, is the mechanism that made increasing complexity possible by slowly increasing the number of ways we had at our disposal to tap into energy flows. 53
    3) Increasing Control of the Biosphere's energy and resources: The third theme concerns the energy and resource flows that were made possible by collective learning, and that allowed the build up of the extreme complexity that characterizes our species today. What this theme reminds us of is that we depend on the biosphere. That's where we get all that energy from! We are an integral part of the biosphere and every significant turning point in human history reflected changing relations with the biosphere. Societies that can mobilize more energy and resources may flourish, but societies that fail to mobilize enough may fail, a theme that is at the centre of Jared Diamond's recent bestseller, Collapse. 54
    Not a deterministic picture: I should stress that I am not offering a deterministic account of human history. The notion of complexity is a way of stressing what all historians know—that human history is unpredictable, quirky, not subject to simplistic laws of development. Individual and collective choices are real. But the argument presented here does suggest that, beneath this astonishing complexity, there are large trends, which can help us make sense of that complexity. It is my belief that world history can understand the unique details of human history only if it also keeps its eye on these deeper patterns. The core pattern is a slow but accelerating increase in complexity, associated with many about turns and retrogressions, and perhaps leading ultimately towards disaster. But, for better or worse, the pattern seems to be real and seems to link human history with larger trends in the history of the universe as a whole. 55
        If I am right that these themes really are central to human history, then what should we pick as the major turning points in that history? The following list is rudimentary, but it highlights what I would pick as the six key turning points in so far as these themes are central. It should be obvious that any list of major turning points, such as this, carries implications for the way we design syllabi in world history. 56
    Crucial Turning Points in Human History:  
    1.     Human origins & collective learning: These arguments highlight the importance of the moment at which humans first began to adapt using the new mechanism of collective learning, about 200,000 years ago. Collective Learning is what set us on the trajectory that made us the most complex thing we know. We are using the most powerful adaptive mechanisms available, a mechanism that, as far as we know, no other species uses. In this sense, collective learning defines human history and world history! This perspective suggests that one of the central themes of world history should be the study of how humans have shared information in ways that that allow them to gradually accumulate more and more powerful ways of extracting energy and resources from their environment. What factors encouraged the sharing of information? What storage methods made that storage more reliable? What factors reduced the efficiency of storage networks? What technologies encouraged exchanges over larger and larger areas? The expansion and efficiency of networks of information exchange ought perhaps to be one of the central ideas in human history. 57
    2.     The Paleolithic: The impact of collective learning is apparent not just in recent history but in the 200,000 or so years of the Paleolithic era. In the Paleolithic era, human communities found many new ways of extracting energy from different environments. Though change was slow by modern standards, increased mobilization of energy from the biosphere can be seen in human migrations to new regions (which required new energy-extracting techniques), and increasing populations. But it also shows up in other changes such as the increased capacity of humans to extract energy by using fire and improved hunting techniques that led, in some areas, to the extinction of many species of large animals or megafauna. Increasing access to energy flows begins in the Paleolithic, so this era is the foundation of world history. 58
    3.     The origins of Agriculture: Nevertheless, the appearance of agriculture does stand out as marking a sharp increase in our capacity to control energy. What humans began doing was diverting large flows of energy towards themselves. In a farmer's field, the total generation of energy from photosynthesis usually declined, as farmers cleared away many photosynthesizing organisms. But the amount of energy diverted to human uses increased, as humans preserved and tended only those organisms they could exploit. So agriculture is really about diverting more and more of the biosphere's energy towards our species. 59
    4.     Cities and States: The increasing energy flows made possible by agricultural techniques encouraged population growth, which, in turn, encouraged increasing social complexity, as societies became larger and more intertwined and began to require more complex forms of regulation. Cities and states appeared and they, in turn, stimulated collective learning because they managed huge networks of information exchange which in turn enabled them to mobilize energy flows over larger areas. 60
    5.     The Columbian exchange: Collective Learning goes global. The Columbian exchange, from the early sixteenth century, stands out because it marks a sudden increase in the scale and power of the networks of exchange between human communities. For the first time, information, ideas, and techniques, began to be exchanged on global scales. Not all historians would agree, but my own feeling is that this is the key to understanding the emergence of modern science and technology. The Columbian exchange marks a sudden expansion in the scale and power of information networks. 61
    6.     The Modern Era: In the modern era, complexity, energy flows and information flows all increased at unprecedented rates. Today, we control many thousands of times as much energy (some would say a million times as much energy) as we did in the Paleolithic era, and that is the basis of the astonishingly complex societies of today. But as we've seen, these changes come at a price. It's been estimated that we may now be controlling between 25% and 40% of all the energy that enters the biosphere through photosynthesis. The more we control, the less is available for others, which is why rates of extinction today are faster than they have been at all but five or six other eras in the last billion years. In other words, this rate of increase in the energy flows we control cannot continue without us doing profound damage to the environment from which we draw the energy and other resources on which we depend. Here, perhaps, is a hint of the fragility that is the complement to our extreme complexity. That fragility is the central theme of one of the best world history books of recent times, John McNeill's Something New Under the Sun. So, in the modern era, we see acceleration, increasing energy flows, increasing complexity and, perhaps, increasing fragility. 62
        I'd like to end by proposing this list as a series of uninvited suggestions for those thinking of possible modifications to the AP World History syllabus! How these ideas might alter the AP syllabus I leave you to decide, but one conclusion is obvious; they would encourage designers of the syllabus to try to embrace the whole of human history rather than starting a mere 8,000 years ago, when the game's already been underway for 200,000 years or more! 63


    PowerPoint Slide 23 -24



        In conclusion, I hope I have managed to persuade you of my central argument which is that big history can illuminate world history just as powerfully as world history can illuminate history at the more conventional scales of the nation state or region or area. 64


    Biographical Note: David Christian teaches Big History at San Diego State University. He is the author of Maps of Time: An Introduction to Big History (Berkeley: University of California Press, 2004).


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