This is part two of a four-part post. See also parts 1, 3 and 4.

One of the key breakthroughs that I made as I read this literature was to realize that there have been a few dominant trends in human history. These trends have so powerfully structured human societies that they must be used as a starting point for understanding human history. While names, dates and events are interesting, these trends are what really matter. And often these trends are not taught in history books.

Among the most important trends have been:

• The gradual expansion of humans from the African Savanna into virtually every ecosystem on the planet.
• The very slow increase in the rate of technological innovation, so slow up until 10,000 years ago that it was almost non-existent. But then the gradual acceleration in the rate of innovation since then, until it has reached a frantic pace today.
• The extraordinarily slow, but still discernible increase in the complexity of technology over the last 200,000 years. As with the rate of innovation, this complexity of the resulting technology has also accelerated over time.
• The very slow increase in the rate of diffusion of technologies and social organizations between cultures.
• The increase in variety and complexity of social organizations.
• The increase of the:
  • Global population size.
  • Population size of a typical community and polity.
  • Population density of a typical community and polity.
  • Proportion of communities with permanent domiciles.
• The decline in the number of societies on the planet over time. This has largely been due to societies with complex technologies and social organizations absorbing simpler societies.
• The gradual reduction in the level of violence.
• (Since 1300) The gradual replacement of forced labor with free labor.

These trends first typically originated in one small geographic region and then gradually expanded until they encompassed continental-size areas. More recently, these trends have affected almost the entire world. While these trends have defined the human experience over the last 200,000 years, they are rarely mentioned in history books except in passing.

In addition, it became clear to me that there have been a few constants in human history as well:

• Energy has always been critical to both survival and change, and the vast majority of that energy has come directly or indirectly from the sun. Food, which is the solar energy transformed into energy that humans can consume, is by far the most important energy source for humans.
• Until recently the vast majority of total man-work hours has been devoted to food. Upwards of 80% of the total man-work hours in history have been devoted to acquiring, preserving, distributing, preparing and consuming food, not to mention the building and repairing of tools necessary for this effort. This has left little time for traditional societies to do much else.
• This massive effort to acquire food has been heavily constrained by geography. Each region offers a very limited menu of natural food options, so humans have been forced to adapt their entire society to those constraints.
• Because there are only so many ways to acquire food and so much work effort has been necessary to do so, the means by which societies acquire their food has been the key determining factor in structuring human societies.
• Technological innovation has been extraordinarily concentrated in cities. While rural areas may innovate new means of food production, virtually all other innovation happens in cities.
• During any one time period, technological innovation is extraordinarily concentrated into just a few cities or nations. These cities or nations shift over time, but the concentration always remains.
• Social organizations, particularly militaries and corporations, are constantly in competition with each other for food or revenue that enables them to survive. Those organizations that are best able to use technology for their own purposes do far better in this competition. Those that fail are doomed to decline and extinction.

As I mentioned earlier, to understand these trends, I read a wide variety of books. Many of the authors proposed one dominant factor as the key driving force in human history: class struggle, climate change, agriculture, military conflict, technology, institutions, trade, biology, disease, economics, demography, geography, family structure, culture, religion, ideology, and many more. The list is dizzying in its length. Most of these authors make persuasive arguments for the importance of their favorite factor, but few of them agree.

After finishing each book, I came away excited from being able to see the world from an entirely new perspective, but also strangely unsettled because each of the authors seemed to contradict each other. Or more accurately, they seemed to ignore each other. Since most of the authors had not read books much outside their own discipline, they never really attempted to deal with the strongest claims of their rivals. I felt, however, that because we only live in one reality, there must be a way to integrate them together into one conceptual framework that helps us understand history.

One of the key problems with many of these theories, is the problem of origin. If, for example, institutions are the driving force in history, as many political scientists believe, where do institutions come from? If economics is the driving force in history, as many economists believe, where does the economy come from? Since each of these “ultimate causes” must have arisen from something else, the problem of origins tends to undermine the explanatory power of those factors, at least when we view history over the very long-term.

Another problem with many of these theories is that the authors usually focus excessively on one time period or one geographical area. Typically, the focus is on Western nations within the late decade, century or last 500 years. The authors that don’t focus on one nation or time period, usually in the very recent past. Some studies, particularly those by anthropologist focused on hunter-gatherers of today or thousands of years ago. Very few examined a wide variety of societies over that last 200,000 years.

Another problem with these theories is that they present evidence almost entirely on the national level, treating all of Britain, China, Germany and the United States as if they were homogenous entities. As any resident in any of those countries can tell you, each of these nations have important regional, ethnic and religious differences. And those difference have often been stronger in the past than they are today.

Go to part 3.