So far, this series has given a compressed tale of human evolution. In part one, I explored the different categories of information on evolution; in part two, I outlined the first six phases of evolutionary change from 500 ka to 25 ka (ka = thousand years ago).
But evolution did not end here.
In this essay—the last of the series—I treat the expansion of human societies after 25 ka as a new phase in evolution. For the previous two million years, human communities gradually expanded from the 40 members that were typical of primate species to 150 members for Homo sapiens. The latter were by far the largest persistent communities of large animals, putting humans at the top of the food chain. There was no clear precedent for the accelerating expansion in human social scale that took over around 25 ka. Multiplication in the size of human groups was neither a natural nor an inevitable process; it broke the deep, existing constraints of hominin social structures.
What aspects of evolutionary dynamics enabled human groups to expand from groups of 150 members to more than a million times that today?
The Seventh Phase of Evolution: The Problem of Expanding Human Scale
Laying the groundwork to explore the dynamics of biological, cultural, and social evolution, the preceding posts in this series have covered six categories of evolutionary analysis:
- Culture 1, or “social learning”
- Culture 2, or “group culture”
Since none of these categories give obvious explanations of expanding human scale, I will now dig deeper to identify specific mechanisms that may help explain the whys and hows of expanding social scales.
Five Possible Mechanisms for Scale Expansion
For each mechanism below, I provide a key question and a brief explanation for the mechanism’s influence on expanding social scales:
1. Anthropological description
The anthropological description implies that foraging groups expanded worldwide by a factor of 10 (up to 1,500 members within 10,000 years), reaching the scale at which surviving foraging groups are known today. Agricultural societies are argued to have expanded by another factor of three (30 times larger than the ancestral community). Anthropologist Harvey Whitehouse links the rituals of the early Holocene—some more complex and demanding than others—to the formation of larger-scale social groups. Such anthropological descriptions, while they are insightful in their detail, do not yet explain the later and larger social scales.
Drawing from anthropologists, I hypothesize three scales of groups that may have arisen:
- “Confederations” (at 20 ka: 500 members or three communities): Communities allied and ultimately integrated with the cold and drought of the Glacial Maximum
- “Ethnicities” (at 12 ka: 1,500 members or three confederations): Intensive food gathering of fish, grains, or animals as the climate became warm and humid
- “Societies” (at 9 ka: 5,000 members or three ethnicities): Agriculture and expanded labor; as at Çatalhöyük with 3,500–8,000 persons in the era 7500–6400 BCE
2. Genetics or epigenetics
At the time of language expansion, genetic changes might have spread worldwide via migration; at other times, genetic change would have spread more slowly. Epigenetic change is best known as development in child behavior, but developmental processes also continue for adolescents and young adults. Thus, shifts in protein interactions might have been provoked through global environment change, leading to development of adolescent and adult readiness to articulate language or to work in larger groups.
Key question: Were there inherent scales for human group size, awaiting the expansion of human population to each level?
Fractals reflect self-organizational of elements in ways that are parallel at multiple scales, thus yielding inherent group sizes. Perhaps the phenotypical scales of human life—simplified into the individual, the household, and the community—underwent subtle changes that enabled larger social groupings to become feasible and valuable.
Robin Dunbar showed that self-organization of groups among all primate species created a hierarchy of group sizes, expanding from scale to scale by factors of just over three. He then combined empirical data and fractal theory to propose “grades” or stable sizes of human groups up to 50, 150 (communities), 500, and 1,500 (tribes). Such grades might be extended, in certain circumstances, to create larger-scale grades such as those for humans after the Ice Age.
4. Phase transitions
Key question: In the same way that physical phase transitions yield sharp phase changes at crucial points—for example, water turning from ice to liquid to vapor—were there also types of social relations that changed greatly because of environmental influences, ultimately creating different overall human patterns and scales?
The physics model of phase transitions helpfully suggests that changes in individual social interactions may bring global changes in social scale. This assumes that molecules within a container have patterns of interaction with each other, which may change in response to external shifts in temperature or pressure. However, such molecules appear much more uniform than human individuals or their scales of individual, household, and community.
5. Scale-free networks
Key question: Were human communities linked to distant others, so that “hubs” of closely related communities formed and, later, expanded?
Among large networks, a “diameter” may be calculated to establish the number of links one must follow to get from one point to another point in the network. The diameter of biochemical cell networks, for example, is about three, suggesting tight connections. The diameter of the World Wide Web is about 19, while the diameter of U.S. society is estimated at six. Although global linkage is relatively easy today, we must consider whether long-distance links among networks were possible in the early Holocene era—and whether such early expansions required thousands of years before accelerating with time.
Summarizing the Possibilities
Studying the mechanisms of changing human social scale reveals intriguing links and comparisons across times from early Homo sapiens up to today. Epigenetic change—if it provokes the creation of new scales—raises the question of whether changes around the world occur at the same time. Fractals, on the other hand, are inherently about replication at multiple stages of growth.
Phase transitions show that small-scale dynamics may bring large-scale results, when accompanied by the right sort of environmental change. And the hubs of scale-free networks point toward great urban centers or earlier commercial crossroads; each hub expansion tends to bring about the next.
Whatever influence each mechanism has had, the human order has expanded over recent millennia by a factor of about a million or 12 powers of three. One may then ask: What were the results and the benefits of expanded scale? Were the benefits shared widely, or were they limited to certain parts of the population or areas of the world?
Scale Expansion in Human Context
Which of the six categories of evolutionary analysis information on evolution tell us most about the expansion in scale? To start, expanded scale is a phenotypical description, focusing on the behavioral groupings of humans rather than individual characteristics. Scale expansion surely brought many genetic changes in its wake. Can one argue the reverse and hypothesize a genetic change that launched the whole process?
Epigenetic change is a more likely causal candidate, as recurring environmental change might have brought new behaviors that facilitated group expansion for children and young adults. (Population has been defined in these posts as a concept including numbers, speciation, and migration, but one can now see that it must also include scale of groups.)
Environmental factors surely also influenced scale—for instance, as certain types of regions encouraged scale growth, or as the long warming of the early Holocene brought added resources to humans. (But did other species expand their social scales in the Holocene?)
Culture 1 (social learning), while it facilitated interaction at a local scale, seems to have functioned for 200 millennia without increasing the scale of the human order. Culture 2 (group culture, which ultimately included language development, visual arts, and accelerated invention), is associated with the initiation of scale expansion, though no detailed mechanism has yet been articulated.
The above mechanisms, arguments, and hypotheses show that there is much to be discovered when it comes to understanding the precise evolutionary processes responsible for the expanding scale of social organization. One question looms largest: Will these and future ideas ultimately reveal a clear explanation of expansion in human scale, or will they tell a tale of multi-pronged transformation?