The outline below considers human experience from the standpoint of three magnitudes:
The proto-hominids underwent a succession of evolutionary changes that produced the modern human being by about 100,000 years ago. Over this long period of time, hominids began to rely more and more on learned behavior for their day-to-day survival.
The shift from instinctive to learned behavior made hominids more and more flexible. The elaboration of language may have been a key expression of this flexibility. As human mental capacity grew, though, hominids acquired a new relation to the future. Animals live in the moment and react only to stimuli that they can sense. This sensing does not extend far into the future. Humans began to imagine future needs and wants long before they could be sensed. This ability created new uncertainty as well as new flexibility. Religious beliefs met the most long-range needs for stability and certainty.
Human life by the end of the stone age was thus a paradox. We became human by becoming more reliant on learned behavior (on our minds), which made us more flexible. But we also wanted security, and we eventually felt a need for something eternal. When people settled into fixed and inflexible ways of life, they failed in the long run to achieve security. But people also needed a degree of stability in a world of change. Finding a path between the need for continuity and the need for change has been the challenge to human existence ever since. The path of human cultural evolution has been one in which the insecurity of daily life has diminished but in its place uncertainty about larger and deeper things has grown.
These four periods were not identical in degree: the Atlantic period was warmer than the Sub-Boreal and wetter than the Sub-Atlantic, which in turn was not as cool as the Boreal.
Climate change has disrupted Holocene civilization twice. The onset of Sub-Boreal conditions caused river civilizations to break down as pastoral peoples migrated into them from the grasslands. The great civilizations of the classical world emerged when environmental conditions stabilized after 1000 BC.
The northern hemispheric temperate rainfall belt shifted to the north between 200 and 1200 AD, drying out the grasslands again and causing a new wave of pastoral migrations. Since the rise of modern civilization after 1500, settled societies have been dominant. But climate is now entering a warming phase aggravated by recent human activity, and social breakdown could occur again if settled societies are unable to adapt to climate change and mitigate its effects.
Human life in the Holocene has had three cultural inflection points: the breakthrough to farming around 8000 BC, the breakthrough to civilization by 3000 BC, and the industrial revolution (c. 1800-2200 AD). Three shifts in outlook have coincided roughly with these points: a search for causality in the world, a search for lawfulness in a world of causality, and a search for control in a world of lawful causality.
Material Life. Settled farm life seems to have emerged by 8000 BC. Over the next five millennia, larger towns developed around the world with more complex divisions of labor. The resulting civilizations began to form territorial states after 3000 BC. A more global civilization has been emerging since 1800 AD that could take the form of a world state one or two centuries from today. However, many challenges will need to be overcome if this degree of unity is to be achieved and sustained.
Outlook. Early farmers believed that arbitrary supernatural beings controlled the processes of nature and could be influenced through sacrifice and other ritual activity. This archaic idea that the world had meaning, that effects had causes, was a primary conceptual breakthrough. It began the process by which human understanding began in the classical period to embrace notions of general lawfulness in nature and human life. In the modern period, humans began to believe that they could understand and control a fully lawful nature. Our future will depend on whether we can exercise this control responsibly.
Overview. More detailed generalization about the three millennia since 1000 BC is more difficult because we do not have a long enough perspective. However, it is convenient as well as conventional to divide the interval into three periods in which change can be measured in centuries. During a classical period beginning around 1000 BC, large areas of human settlement came together in great civilizations. These civilizations broke down in the first millennium AD. During a medieval period from about 500-1500 AD, the major cultural areas of the planet either recovered or developed partially new identities. In the five centuries of the modern period since 1500, the process of wider integration has resumed. Europeans dominated this process initially but a single modern global civilization may now be emerging.
The Future. Modern civilization has given people more freedom and choice in their lives, but it has also challenged at deeper and deeper levels ideas of what is immutable and intrinsic. A sense of anomie and alienation has accompanied modern civilization as a result, and whether this is a transient or chronic condition is not clear. The world was fortunate to survive the totalitarian horrors of the twentieth century, but alienated people and the causes of their alienation continue to threaten the modern world. New pressures on the natural world pose even greater danger.
The classical period was an age of expansion and integration. The medieval period was more stable and inward-looking. The modern period has been another age of expansion and integration. If global standards of living rise to a common average in about two centuries, society may again value stability more than change. The result could be a culture in which intrinsic values are less besieged by utilitarian ones. In a more settled future, the most important questions may then be whether humans make contact with intelligent beings elsewhere in our universe and with other universes or planes of existence beyond it.
A yearning to explore new frontiers and to experience new challenges will continue for some and perhaps revive as an urge by all someday. In the long run, astrophysical events will require humans to be more adventuresome if the universe as we currently understand it continues to be our home.