Course Summary: “Principles of Human Ecology” by Peter Richerson et al

Title: Principles of Human Ecology
Author: Peter Richerson, Monique Mulder and Bryan Vila
Scope: 5 stars
Readability: 3 stars
My personal rating: 5 stars
See more on my book rating system.

Topic of Book

This “book” consists of the syllabi and notes for a college-level course on Human Ecology at UC Davis. Along with the Gerhard Lenki books summarized earlier, they are an excellent overview of human societies. Like Lenski’s book, they rely heavily on the concept of Society Type.

Other books by the same authors

Key Take-aways

  • Concepts and methods shared with the biological sciences are useful to understand human behavior and societies
  • Human societies are best categorized by how they produce their food.
  • The most important society types are:
    • Hunter Gatherer societies
    • Fishing societies
    • Herding societies
    • Horticultural societies
    • Agrarian societies
    • Commercial societies
    • Industrial societies

Important Quotes from Book

What is human ecology? Human ecology is an approach to the study of human behavior marked by two commitments. First, human ecologists think that humans should be studied living systems operating in complex environments… Second, human ecologists think that humans are subject to very similar ecological and evolutionary processes as any other species. Of course, humans are unique, and this fact has important consequences.

THE PRACTICAL MESSAGE: We do not yet know enough about humans to reliably control our more dangerous and destructive behaviors.

The basic rationale for human ecology is that concepts and methods shared with the biological sciences ought to be useful to understand human behavior.

The ecological perspective has been responsible for some of the greatest successes in the social sciences, and it is really the only perspective to offer a plausible scheme for understanding human behavior synthetically.

Humans are a problem for modern Darwinism mainly because of the complexities caused by culture.

Steward was one of the pioneers of the field of cultural ecology. One of the great contributions of cultural ecologists was to furnish us with a taxonomy of human cultures based on subsistence relations. We will use this taxonomy in this course. It turns out to be a great scheme to systematically organize the great mass of things we know about human behavior. Ask Steward’s first question How do they make a living? and much else falls into place.

One might go so far as to say that the main human genetic adaptation is the neural and anatomical machinery to use culturally acquired technology as an adaptive device.

A second important issue is that many cultural behaviors don’t look very adaptive.

The discovery of human diversity is the great contribution of classical anthropology, archaeology and history.

The advent of the voyages of discovery late in the 15th Century greatly increased contact with more distant societies, but appreciation of the nature of human diversity was quite poor until a more scientific approach to exploration was begun in the latter part of the 18th Century.

Only in the last decade have comparative psychologists come to have a reasonably clear picture of how much social learning takes place in animals. The general answer is clearly that many examples can be cited in birds and mammals, but certainly the capacities of culture in animals are much more modest than in humans… Imitative tasks that humans find quite easy, even our relatively big-brained primate cousins find virtually impossible!

Julian Steward’s 1955 book “Theory of Cultural Change” was important because it was the first synthesis of the discoveries of human diversity and uniqueness using ecological and evolutionary ideas… He gave us a simple, workable model of adaptation to environment via culture.

The basic method Steward advocated was to trace the effects of environment, acting through technology, as deep into a culture as the effects actually went. Recall from the first part of the lecture the key role of technology for Steward’s method.

He was reacting to two other views he considered oversimplified. The first was environmental determinism, championed by a geographer, Ellsworth Huntington.

Steward’s second procedure was to trace the effects of technology to patterns of social behavior, especially the organization of work.

Steward’s most famous example is the way the organization of hunting and gathering work varied as a function of environment in North America.

The third procedure was to trace the effects of technology and work organization as they affect other parts of culture. For example, the demography of a society, including such things as its total size and the size of individual settlements, is a function of economic productivity. The amount of resources a society can obtain depends upon the environment, the technology, and how effectively work is organized. Total size and settlement size in turn affect the economic division of labor. Large societies can support craft specialists, like weavers and potters who make tools for everyone else and trade for food. In small societies, craft specialization is curtailed; everyone has to make tools for themselves because the number of potential customers is too small to support a specialist.

Steward’s main ideas are summarized in his concept of the culture core. The culture core is those features of culture that really are illuminated by the technological window. They are those features that are related to the work of making a living in a particular environment.


Technology is the “window” through which people look at their environment. Our adaptations are mainly technological, and how we interact with any given environment depends first of all on the tools we bring to that environment.

The highly social nature of humans is unusual. Most animals are more like bears than humans–solitary and hostile. large-scale cooperation with non-relatives is especially unusual.

At a given level of technology, culture core variables should be a strong function of environment; environmental determinism should work well enough within sets of societies deploying a similar technology.

Demography is a key variable relating environment to many culture core features.

Hunter-Gatherer Societies:

The single most important consequence of hunter-gatherer technology is that it ordinarily supports very low human population densities.

Not only were the densities of most hunters and gatherers low, but typical settlement sizes are also small.

The typical hunting and gathering band must move frequently, often as frequently as every few days.

Hunting and gathering technology typically results in very simple social systems.

Knauft (1988) has recently emphasized that the murder rate is remarkably high in all the well-known politically very simple societies due to the use of self-help violence. (This category includes some tropical horticulturalists, and most contemporary hunter-gatherer groups, that are characterized by very small settlements, low population density, and strongly egalitarian social systems.)

In spite of hostile relations, trade was often moderately important to hunter-gatherers.

The culture core idea works for hunter-gatherer societies.

Horticultural Societies:

Horticultural societies have agricultural systems that are relatively unproductive per unit of human labor compared to plow agriculture, and more productive per unit land area than hunting and gathering.

Despite the relative simplicity of the technology, something like a 100 or more domesticated crops are kept, and plots are botanically complex.

In the poor soil regions of the very wet tropics human densities under horticulture are often very low. In Amazonia and lowland New Guinea, densities are well within the range for hunters and gatherers, a fraction of a person per km2

In general horticulture is capable of supporting as many or more people per unit land as under the plow, just with more human labor per unit of yield.

More typically, horticultural societies are either organized around “Bigmen” or Tribal Chiefs.

In the simpler horticultural societies, differences compared to hunters and gatherers are, to repeat, modest.

In many horticultural societies, women contribute disproportionately to subsistence activities because they are responsible for most of the gardening work… Polygyny is also common in horticultural societies for the same reason. When women are the principle wealth producers, a man may get rich by having several wives. Men seem rather parasitical in horticultural societies, because they often do relatively little subsistence work but arrogate to themselves important political and military roles.

There seems to be a strict limit to the number of people that can be organized politically under the big man system, only up to a few hundred people.

Political systems based on hereditary politicians (Chiefs) organize fairly large-scale political units. Chieftainships have a hereditary principle of political power, and, as they are elaborated, evolve into the ascriptively stratified societies so common historically.

Warfare is typically much more important under horticultural than hunter-gatherer technology… Terroristic practices such as headhunting, headshrinking, scalping, and cannibalism are commonly practiced by horticulturalists.

The ecological and humidity gradient from the Pacific across the Andes into the Amazon Basin is one of the most spectacular in the world. It provides an excellent example of how the same basic subsistence system can lead to very different outcomes in different environments by the Stewardian culture core mechanism.

The human ecological gradient was equally sharp. The wet Eastern lowlands were the home of simple horticulturalists and hunters and gatherers. The intermontane valleys and miniature Niles along the Peruvian Coast were host to sophisticated chiefdoms, citystates, and ultimately the Inca Empire.

Pastoral Societies

 Pastoral societies are those that have a disproportionate subsistence emphasis on herding domesticated livestock… The most important defining criterion perhaps is the organization of community life around the needs of the herds. Typical herding societies are “nomadic.”… Nomadism is a technological adaptation to scarce and ephemeral pasturage that has major ramifying effects on culture core features that are absent if animals are managed from a fixed home base.

Pastoral societies are theoretically important because they exhibit non-progressive evolution.

Imagine how the history of the Old World might have differed if the ratio of the grasslands favorable to pastoralism to those where the farmers could dominate had been, say, twice as great as it was.

The technology of pastoralism is largely just the animal husbandry component of the prevailing horticultural and agrarian technology, more or less thoroughly shorn of its plant cultivation component.

Thus animal specialists are often motivated to trade much of their valuable animal production for grains, crafts and manufactures, luxuries and so forth. Settled peoples often pay tribute to pastoralists to avoid raids, or pay some pastoralists to protect them from other pastoralists.

 The key to the culture core of pastoralism is the mobility made possible by herders. Quite small groups, usually a patrilineal extended family that collaborates to manage one herd, is the basic social unit. It can operate as a nearly autonomous social system with tenuous ties to other families. However, mobility means that many such units can potentially assemble in one place. Thus tribes and confederations of tribes can also arise. Historically, the scale of pastoral societies tended to fluctuate unpredictably. More often than not, pastoral societies were small and independent, with much conflict between tribal segments within ethnic groups. In the great waves of conquest in the Old World, multi-ethnic confederations arose.  The Mongols organized an imperial state on the basis of nomad conquest.

Pastoral societies are tremendously variable in terms of the details of their technology. Perhaps the most important distinctions are those based on sophistication of transport methods. The pastoralists of the Eurasian Steppe, including Indo-Europeans in the early days, Turks and Mongols later, made extensive use of wheeled transportation, as well as riding horses. The Camel nomads of the Eurasian and North African deserts rode but seldom used cartage. The late, specialized North and South American equestrian hunters were similar to the Arab Bedouin in this respect. Finally, the Eastern and Southern African cattle herding pastoralists used neither carts nor riding animals. Their toolkit and social organization is more horticultural than agrarian… Carts allowed Eurasians to carry a larger fraction of the agrarian toolkit around with them, and to assemble and supply larger collections of people in one place. without having a very complex political system.

 Pastoral societies were absent in the New World.

 The sexual division of labor is sharply marked in pastoralist societies. First of all, men are often largely responsible for herding larger stock such as cattle, whereas women engage in handicrafts, food production and processing, small-stock herding (goats, sheep) and the milking of livestock at camps. The division of labor is underlined by the grossly disproportionate emphasis on masculinity in these societies.

By discovering the fundamental tactical advantages of movement, concentration, surprise, and offensive violence, pastoralists could defend themselves from numerically and technically superior armies of states.

 The evolution of pastoral military institutions tends to snowball. In the first place, herd animals are relatively easy to rustle, and pastoralists everywhere are in the habit of stealing from each other. Rustling keeps fighting skills tuned to a high pitch. Furthermore, the pastoralists’ skills are quite suited to general banditry and raiding on the agricultural fringe.

The main deterrent to pastoral conquest of states is the relatively small size and mutual hostility of the pastoral tribes. However, as the Sioux-Cheyenne confederation at the Battle of the Little Bighorn illustrates, sometimes the tribes can unite, and the inherent power of pastoral mobility can be increased sharply, both because of less need to protect the grassland rear, and more warriors for the raid or assault. Once a few tribes unite, they are in a position to use the carrot and stick on still other tribes. The choice is: join the confederation for a great raid, or die!

In all, civilized Eurasian suffered 4 major invasions, the Indo-Europeans (ca 5,000 BP), the Hun and German invasions just mentioned, the Arabic expansion in the 7th Century, and the Mongol invasions of the 13th Century.

Agrarian Societies

As agrarian technology developed, the potential for substantial gains in per capita production arose as more sophisticated technology was put into farmers’ and artisans’ hands.  Gains in production per unit of land and per unit of human labor have somewhat different implications for culture core traits, as we have already noted.

The tragedy of agrarian societies is that this potential was not generally realized. A combination of exploitation by elites and population growth tended to erase any gains in well-being for most cultivators. This is essentially the argument of T.R. Malthus.

The defining trait of agrarian technology is the presence of plows and draft animals. No single technical principle has proven quite as important as the idea of substituting non-human power for human labor.

 Heavy plows were responsible for the medieval economic and socio-political revolution of Europe. Heavy plows were known in Roman times, but only came into widespread use in the Medieval period in Europe, where they allowed the cultivation for the first time of the heavier, wetter, inherently more productive soils common north of the Alps. Prior to the extensive use of moldboard plows, Northern European settlement was mostly confined to belts of lighter soils that could be farmed with the scratch plow. As late as 1000 AD 80% of Europe was still covered by dense forest and was only opened to the plow by a wave of pioneering that lasted until 1300 or so.

Many scholars have suggested that innovations tended to come in irregular bursts, and that long periods of near stasis were the rule.

Agrarian technology permitted urbanization of population to a greater extent than was possible under horticulture.

Under agrarian technology men’s labor becomes relatively much more important, chiefly because managing large animals is almost always, like hunting, men’s work.

 Agrarian societies are especially noted for their extremes of social stratification. The high-ranked lineages of tribal horticultural societies become (typically) a much more exalted ruling class, still typically combining religious and military institutions to justify and enforce their domination and support elaborate patterns of consumption. Slavery, serfdom, or peonage is commonly the lot of the primary producer. The emphasis in the modern West on personal liberties and freedoms (and in the Marxist countries on economic equality for that matter) was in large part a reaction to the steep and rigid stratification of agrarian societies.

 Increasing social stratification is linked to a more developed division of labor.

 The main institutional innovation of agrarian societies is the state.

 On the one hand the state is an effective institution to manage the immense redistribution required if productive farmers are to be linked to specialist producers of metal tools, cartwheels, cloth, and the like.

 On the other hand, the productive division of labor of agrarian societies is a strong temptation to the guileful priest and the greedy warrior. These two classes often combine to extract a scandalously disproportionate share of the farmers’, artisans’ and traders’ efforts.

States begin to control internal violence by enforcing a rule of law.

 One apparent consequence of the political complexity of states is that they tend to be unstable. Dynastic changes, foreign occupation, and the collapse of imperial states into smaller constituent city states, even the regression of states to the tribal scale of organization are common. Further, it is common for large states and empires to co-exist in similar environments, using similar technologies, with small city states or even tribal societies.

Commercial/Industrial Societies

By one useful definition, commercial and industrial societies are those with less than half of their population engaged directly in agricultural production…  Perhaps the most important point is that these societies, in contrast to the agrarian or horticultural type, are not dominated quantitatively or qualitatively by people with a direct interest in food acquisition.

The key initial development of commercial/industrial technology was a cheap means of seaborne transportation. The improvement of sailing ships to 100+ tons was, in hindsight at least, one of history’s most pregnant developments. All-weather, seagoing vessels that could navigate the length and breadth of the Mediterranean and carry on a trade with Northern Europe were available by about 1300.

The degree of occupational specialization increases dramatically in commercial and industrial societies.

The social structure of commercial and industrial societies is quite unique in the numerical predominance of a middle class based on achievement.

Modern middle-class child-rearing styles resemble those of hunters and gatherers more than they do those of the peoples of agrarian states. The stress is once again on relatively relaxed discipline, and on the encouragement of independence.

What Steward’s culture core concept lacks is a precise account of the mechanisms by which adaptive variations within technological types arise, and how evolutionary transformations between technological types occur. Ecological anthropologists like Steward developed a very successful descriptive scheme, but a less impressive explanatory system.

The Key to Population Thinking:

Pay attention to what individuals do in the short run. Then add up over all the individuals in the population, and imagine the same basic processes go on for many generations. Do the arithmetic and see what ought to happen.

Often the very simplest calculations give you 50-75% of the insight into causal processes that could be obtained from the full-blown theory at a small fraction of the work.

Culture as a mechanism for inheritance of acquired phenotypic variation.

Culture is socially learned information capable of affecting individual phenotypes. People acquire culture from other individuals, via teaching or imitation.

The claim advanced by Campbell and defended here is that the differences between genes and culture are very important, but that Darwinian methods are equally applicable to both because of the key similarity of transmission of information by variable individuals through time.

You’ve all heard of the “nature-nurture” debate. This debate is confused because it lumps culture—transmitted effects that are very gene-like—with direct effects of environment on behavior through individual learning and the like. It is very important not to confuse environment and culture.

Genes are a complex DNA-based inheritance system which is often associated with the concept of ‘nature.’

CULTURE is acquired via social learning or imitation from other individuals.

Environment consists of things and processes that are external to the organism or population being studied.

What culture an individual gets depends on the population in which it lives. Two individuals that have very similar genotypes, and live in the same environment, may behave quite differently if they have been socialized by different cultures.

In the short run, cultural tradition was more important than individual or group choices, decisions, and learning. But over the longer run, changes were accumulating. This is consistent with an evolutionary model of cultural transmission.

When environments change very rapidly from generation to generation, but without any overall trend, any form of information derived from the experience of parents via learning or selection is useless. In this situation, the fixed learning rule is best.

When environments change very slowly, selection on genes causes the genetically transmitted guess to track the environmental change almost perfectly, and any individual learning is disadvantageous because of the extra costs and errors caused by learning.

When environments change at moderate rates, the inheritance of acquired variation is a virtue. Cultural transmission can track environmental change faster than genetic transmission because both guided variation and selection are acting together. Human societies exhibit cooperation, coordination, and division of labor, three features that place them at striking variance with most animals

Highly social animals are rare, and basic Darwinian analysis shows why (Alexander, 1974). An animal’s conspecifics, members of its own species, are its closest competitors for food, mates, shelter, and so forth. Groups are likely to be easier for predators to spot, and group living ought to favor the spread of diseases. The theoretically most interesting problem is competition. Why should any animal help its competitors?

Animals are thus usually solitary, staying as far away from their fellows as is practically possible. In most mammals, the contact between the sexes is limited to mating, and “society” consists of the minimum coordination between adults necessary for fertilization, mothers’ contribution of resources to juveniles to the point of independence, and no division of labor at all.

Even in the case where animals do live in groups, the degree of cooperation, coordination and division of labor within groups is usually very modest. For example, in herds of grazing animals or in schools of fish, there is virtually no cooperation, or division of labor.

There is just a system of coordinating movements.

In essence, in a selfish herd animals are hiding behind each other.

When cooperation does exist, the groups are typically very small. Many birds form

mated pairs that cooperate to raise a nest of young, but bird flocks, when they exist, are selfish herds. A division of labor is even rarer, aside from those differences directly enforced by the biology of sex. Even in the case of sex, the commonest form of “division” of labor is that males contribute less or nothing to the rearing of offspring compared to females.

Why is it so hard for cooperation to evolve, if it is so successful when it does evolve?

This is a classical problem. Economists have analyzed the problem under the heading of the “public goods problem”. Game theorists have dealt with the same problem in their research into the perverse logic of the “prisoners’ dilemma game”… In all of these manifestations, the problem is that the altruistic self-sacrifice of individuals for the common good is hard to explain.

Commerce and Trade

The economic advantages of the division of labor are quite large… Yet, relatively few species have evolved a division of labor and the human expansion of the division of labor to create modern economies is a very late process. The key question is “Why is it so hard to achieve a division of labor?”

There must be some serious impediments in the way of a free evolution of a division of labor. We argue that the primary problem is one of cooperation. A division of labor generally requires that partners be able to resist taking unfair short-term advantages.


War is one of the most dramatic types of interactions between human groups. Indeed,

it is one of the most dramatic types of human behavior. It is also arguably one of the most important types of interactions in terms of its effects on the sizes and distribution of human populations and on the human evolutionary process in general. It is also one of the most characteristically human kinds of behavior. Other animals often fight, but very few of them fight in large, organized groups against other large, organized groups the way humans do.

Only humans have the requisite levels of cooperation, coordination and division of labor.

Diffusion of Innovations

Diffusion of innovations between societies is one of the most important processes in cultural evolution. The diffusion of innovations is important because it is relatively hard to invent (or develop) many kinds of useful knowledge. Complex techniques (e.g. maize farming) are combinations of many skills, and develop over a long period of time. It is usually difficult to invent all the requisite parts in the right order, foresee the advantage of nascent new technology,etc. It may also require a special environment or a historical/cultural preadaptation to make the earliest steps of an invention possible. It is usually much easier to acquire all but the simplest skills from someone else than it is to try to invent them for yourself.

Most societies have undoubtedly acquired most of their cultural repertoire by diffusion.

If you would like to learn more about human ecology, read my book From Poverty to Progress.

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