Lucas Bowman. 21st Century Anthropology: A Reference Handbook. Editor: H James Birx. Volume 2. Thousand Oaks, CA: Sage Reference, 2010.
While researching for this entry on human ecology, the author perused books and articles about ecology, biology, geography, and anthropology; human ecology uses all these disciplines, and more, toward its own end. Human ecology refuses to condense its focus into one approach; it investigates many approaches to a problem. This investigation method involves all the above mentioned disciplines. However, because its focus is so broad, no one agrees on a concrete definition of human ecology. In an attempt to reveal its definition, this article describes theories, research, and case studies in this field.
What happens when the two words composing human ecology are defined separately and then combined? A common definition for human is “a bipedal primate mammal (Homo sapiens): man” (Mish, 2004). Such a definition is easy to understand in nearly any context, but defining ecology may prove more difficult. Levine et al. collect various definitions in the introduction to their book, Human Ecology (1975). For example, German biologist Ernest Haeckel defines ecology as “the body of knowledge concerning the economy of nature—the investigation of the total relation of the animal both to its organic and inorganic environment” (Levine et al., 1975, p. 1). American ecologist Eugene Odum defines ecology as “the study of the structure and function of nature” (p. 1). These definitions are great abstractions of the word ecology; but what is the simple dictionary definition? Ecology is “a branch of science concerned with the interrelationship of organisms and their environments” (Mish, 2004). If human ecology is interpreted as literally the ecology of humans, then, logically, it is the study of relationships between humans and their environments.
Is this definition too base for science? Sargent defines human ecology as “man’s relationship to all systems of life” (1983, p. 3). Strictland and Ulijaszek, authors of Seasonality and Human Ecology (1993), define human ecology simply as “the study of interrelations that exist between individuals, populations and the ecosystems of which they are a part” (p. 1). Sociologist Robert E. Park felt human ecology was the study of processes or systems that develop to upset or align the biotic balance of equilibrium (1961, p. 29). There is a common theme among these mentioned definitions: relationships. Relationships are a large aspect of human ecology, but they do not constitute its entire scope of study.
In his article, “Human Ecology and Interactional Ecology,” James Quinn (1940) examines four views of human ecology. The first is J. W. Bews’s vision of human ecology as an all inclusive science composed of sociology, psychology, geography, biology, and anthropology; the second is H. H. Barrows’s view of human ecology as synonymous with human geography; while the third sees human ecology as solely sociological (Quinn, 1940, p. 714). Quinn rejects each of these proposals and declares his own theory as the fourth viewpoint: Human ecology borrows from sociology, biology, and geography to form separate branches of science beneath each discipline. These branches are under the name human ecology; the branch from sociology is called interactional ecology, the branch from biology is called general ecology applied to man (Quinn had not proposed a working definition for this branch), and the branch from geography is called human geography. Quinn’s theory is represented by three circles (one each for sociology, biology, and geography) situated as a triangle with each being cut in half by a fourth circle (human ecology) in the middle. The author of this entry agrees with Quinn’s diagram because it represents human ecology as its own science, borrowing some, but not all, of its principles from other sciences. However, the author feels human ecology is an opportunistic science that can borrow from all sciences (not just sociology, biology, or geography) to understand a given problem. With this additive, human ecology becomes the holistic view it is.
Indeed, human ecology uses all sciences as a working foundation to solve problems between humans and the environment; however, there is much disagreement about its origin. Hawley (1986) attributes human ecology’s beginning to sociologists. These sociologists looked to contemporary ecologists’ work on the role of floral communities within an ecosystem as being comparable to the role of groups and individual humans within a human ecosystem. Sociologists such as Park (1936, 1961) and McKenzie (1934) established the idea of “an association of species joined in a division of labor and thereby forming a distinguishable adaptive unit” (Hawley, 1934, p. 2). In Hawley’s view, the most central idea to human ecology is the adaptation process. As different flower species share labor to create their similar spatial environment, so do different human groups interact when adapting to their shared spatial environment. A common theme in all studies under the name “human ecology” is a focus on what people have done, are doing, and will do within their environment and whether these actions affect their success or failure at preserving the environment. Basically, human ecology studies the relationships between environmental and human systems.
Even though human ecology borrows from sociologists’ theory, human ecologists ask questions that span many disciplines. A human ecologist asks a series of questions any one scientist would not, such as how do people’s interactions with each other affect land use practices? In researching this question, one could find that human interrelations are influenced by success or failure of crops. Researchers would then investigate why a harvest was sufficient or insufficient. If it was insufficient, did erosion cause a strain on crop yields? What caused the erosion? If it was sufficient, did land use practices cause success? And so on. A human ecologist does not stop after the first question is answered. Casey and Schwartzberg provide an exemplary definition of human ecology as a holistic science when they describe its scope as covering relationships between human populations, the environment, technology, human organizations, and social psychology (1969, p. 3). Being holistic, human ecology absorbs sociological ideas, as well as ideas from many other disciplines, to answer questions.
In contrast to Hawley’s (1986) placement of human ecology as a category of sociology, Sutton and Anderson argue that it falls under anthropology and adheres to the scientific method (2004, p. 7). In the 1940s, anthropologist Julian Steward proposed the theory of multilinear evolution and labeled it cultural ecology. This theory placed subsistence practices at the center of cultural development but allowed cultural evolution variations within each subsistence practice. Leslie White (1949), also an anthropologist, wrote that cultural evolution was directly related to how efficient a culture was at harnessing energy. His ideas of evolution spurred further study of relations between humans and their environments and how these interactions are played out (McGee & Warms, 2004). Although human ecology has sociological and anthropological roots, its development has transcended the bounds of either field.
Moran suggests human ecology is an enveloping discipline that includes at least “anthropology, geography and sociology” (2000, p. 4). Indeed, because it is holistic, human ecology utilizes these disciplines, among others, to solve its questions. When using a holistic view, it is important to remember that parts are not greater than the whole, nor the whole greater than its parts. Steiner echoes this with his own statement about holism: “The whole would not exist without the parts; the parts would not be without the whole” (2002, p. 36). Following this quote, human ecology acts as a connection between the parts of science but does not completely adhere to a single discipline. Just as connective tissues in the body are part of neither the bones nor the muscles they connect, so human ecology is not wholly a part of any science it chooses to incorporate.
Using this myriad of definitions, human ecology materializes as the study of relationships between human adaptive systems and the adaptive systems of the environments humans inhabit.
All organisms must choose their method of survival; their choice is based on getting as much energy from the environment as possible while expending the least amount of energy possible. The Canadian ecologist Pierre Dansereau explains how these choices are made using his law of inoptimum, which reads as follows: “No species will encounter a given habitat and find the optimal conditions for its functions” (as quoted in Sargent, 1983, p. 55). This principle explains why humans change environments to suit their needs, or even why certain trees alter chemicals in the soil in their favor. However, to make these survival choices, an organism needs access to an environment. Without an environment, an organism could not exist.
Also imperative for an organism’s survival is other organisms of its own kind (Hawley, 1986, p. 5). This principle is true mainly for reproductive and ecological reasons, but in humans, it is also true sociologically. Choices are made by individuals based upon relationships with other individuals and the environment. Environments also change along with organisms they sustain, because environments and organisms act upon one another and grow together (Sargent, 1983, p. 3). Now, more than ever, humans have the ability to inflict change upon all environments across the globe through their survival choices (Hawley, 1986, p. 6).
Human survival choices have been honed over thousands of years through culture. Culture is conveyed through a system of learned symbols—intentional abstractions of an idea or an action. Using culture, humans have shifted their place within ecological communities and attained dominance over available energy in any given community or ecosystem. They achieved this dominance through learned behaviors, which enabled humans to expand upon existing knowledge. This foundation of knowledge affords humans a great advantage in survival. Each human need not rediscover concepts such as the use of fire, stone tools, or the wheel; humans are simply instructed how to use these tools and survival techniques through culture (Watson & Watson, 1972; White, 1949). Culture is simultaneously an adapter of environments and an element of the environment.
Hawley names two kinds of environmental elements: biophysical elements, including “land features, climate, soil characteristics, plant and animal life, mineral and other naturally occurring materials”; and ecumenical elements, including “ecosystems or cultures possessed by peoples in adjacent areas and beyond, to which access is provided by the existing facilities for transportation and communication” (1986, p. 14). (Note: Hawley uses ecumenic to avoid the confusion that might be created by the connotations of the words economic and social. But the author feels that ecumenic actually creates more confusion due to its modern religious connotation. As Hawley’s use of ecumenic is intended to combine social and economic, the term socioeconomic will replace Hawley’s ecumenic in this entry.) For an example of biophysical and socioeconomic elements working together, Hawley (1986) cites Spencer’s research with inland Alaskan Eskimo depopulation. Traditionally, inland Eskimos traded caribou hides with coastal Eskimos for whale blubber and other supplies that were unattainable inland. When Europeans arrived, coastal Eskimos ceased most trade with inland Eskimos, because Europeans had more attractive trade goods than inland Eskimos. This change in Eskimo life forced inland Eskimos to move toward coastal areas, because they could no longer support themselves without coastal trade. This move is an example of how socioeconomic elements forced inland Eskimos to modify their adaptation systems to biophysical elements.
Both classes of environmental elements have constant and variable conditions. Constant conditions comprise the initial adaptive challenge such as mountains, rivers, flora, and fauna of an environment, but even these constant conditions can be changed by humans. Variable conditions occur after initial adaptation; they deal with time or duration. Unpredictable or irregular events, such as natural disasters, swarms of insects, appearances of new human groups, invasive warfare, and other cultural diffusions are examples of variable conditions existing over time.
To recapitulate, there can be constant biophysical conditions, such as a nearby mineral deposit, and there can be variable biophysical conditions, such as natural disasters. There can also be constant socioeconomic conditions, such as permanent settlements, and variable socioeconomic conditions, such as warfare. The combination of these two elements and their present conditions form a culture’s environment and shape its adaptive strategies.
Parts of North America’s environment have been shaped by the people who lived there. Native Americans lived for thousands of years in North America before European contact. Black, Abrams, and Ruffner (2006) conducted a study in northern Pennsylvania, examining exactly which kinds of trees composed forests, a constant biophysical condition, in different areas. They found that forests in areas of low Native American activity were populated mostly with beech, hemlock, and maple, whereas forests in areas of high Native American activity mostly consisted of oak, beech, hemlock, chestnut, pine, and maple. Their study showed Native American activity paralleled the growth of stands of oak, hickory, and chestnut. Black walnut occurred only near village sites, and its presence had the highest correlation with Native American influence. As several Native American land practices could have transformed northern hardwood forests to oak-hickory-chestnut forests, the group believes Native Americans shaped tree composition within forests through their land practices.
By clearing forests near villages for agriculture, Native Americans encouraged early-succession edge species. Oak and hickory thrive in open fields and clearings, because they are less shade tolerant than other species. Also, Native Americans’ collection of firewood and building material would have increased the chance that oak and hickory would survive, because the Native Americans thinned the forest near villages. They may have been girdling trees competing with the desired species of oak, hickory, and chestnut. These desired species are adapted to survive fire. These fire adaptations include “thick corky bark, a tenacious ability to resprout following top kills due to high root/shoot ratio… and resistance to rot” (Black, Abrams, & Ruffner, 2006, p. 1272). Native American fire practices encouraged “primary forest efficiency” by reducing forest litter to allow easier mobility, increased acorn quality and quantity for winter and spring subsistence, and increased deer herd sizes in certain managed areas. Dendrochronology suggests tree disturbances sharply declined after European contact. During the Late Woodland period and the Historic period, Native Americans were an important source of disturbance for forests.
This case study is an example of constant socioeconomic elements shaping constant biophysical elements. Without Native American land practices, oak and hickory would not have been as populous in the forest as they were. Native Americans certainly influenced where these species grew using constant socioeconomic tactics.
The Earth in Space
Earth’s biophysical environment begins with its mass in space. The earth’s mass determines its gravitational attraction, while the tilt and revolution of earth determines how it receives radiation from the sun. The distance to the sun determines the intensity of radiation received from the sun. Radiation levels are controlled by the solar constant as well as the angle at which the radiation is received. Gravity limits the weight of organisms, because energy is used against the force of gravity; accordingly, gravity limits an organism’s size, because it must support its weight against gravity. Gravity also limits circulatory systems and, in effect, limits organism height. Earth’s gravity retains gases that compose its atmosphere, although lighter gases such as hydrogen and helium can escape (Levine et al., 1975).
Our present atmosphere was created from volcanic eruptions expelling gases from inside the earth’s mantle. These gases consisted mostly of water vapor and nitrogen with lesser amounts of other gases. Water vapors were trapped by gravity, condensed, and fell back to the earth, forming the oceans. The first plants were aquatic and grew near volcanoes in warm pools. Protected from the sun’s radiation by the oceans, aquatic plants received light filtered through water. As oxygen released by plants entered the atmosphere, it oxidized iron and other minerals. When there were no more minerals to use the newly released oxygen, it filled the atmosphere. Due to the sun’s radiation, the initial oxygen transformed into ozone, which absorbed the sun’s deadly rays. As the atmosphere continued to fill with oxygen, less of the ocean was pounded by radiation, and life could expand its borders. About this time, free oxygen respiration systems developed. Oxygen continued to fill the atmosphere, displacing more and more radiation from the surface of the earth, and allowed life to move onto land around 420 million years ago. Such movement onto land was not by animals, but by plants. Plants moved from the waters onto the shores and then further inland (Levine et al., 1975).
Earth has the temperature and climate it has because our atmosphere selectively absorbs radiation of specific wavelengths. Weather is created through air and water molecule movement powered by the sun’s radiation. Weather is a real-time experience, whereas climate is an abstraction that represents a region’s average weather over time. Topography and distribution of land and water can affect climate in various ways (Levine et al., 1975). By creating rain shadows, topography can form areas of lower precipitation. Rain shadows occur when water-laden clouds lose their moisture before rising over mountains. On the mountains’ leeward side, it is dry, because little moisture can travel over the mountains. Large water bodies heat and cool more slowly than land bodies, and this can affect where and how quickly moisture is absorbed into the atmosphere. Vegetation can also have an impact on weather, such as cooling the air, causing precipitation.
Without soil, there could be no vegetation. Soils are formed by water, chemicals, wind, and living organisms on bedrock (parent rock). Bedrock controls basic soil composition (Levine et al., 1975). For example, sandy soils usually occur over sandstone; chalky soils occur over chalk; clay soils over shale; and rich organic soils over peat. Soils of the same character can spread across different rock types, and so, when forming soils, climate and vegetation can be just as important as rock type. Soil is a mixture of organic and inorganic components (sand, silt, and clay). The mixtures of these inorganic materials control soil texture and its ability to retain moisture and nutrients. Organic matter changes the physiochemical properties of inorganic materials and is food for microorganisms as well as plants. Molecular space between solid soil particles is filled with either gas or liquid. Liquid is a complex solution and is the medium by which nutrients move to microorganisms and plants. Gas in soil is essentially air. Air is normally saturated with water vapor and can contain much larger amounts of carbon dioxide than air in the atmosphere. When soil is waterlogged, it can no longer exchange gases with the atmosphere or aerobic life forms (Levine et al., 1975).
All of these above factors govern the earth’s dimension and environment, and they form the land humans live on. Land is not all the same due to topography and climate. Humans prefer land with good soil, a water source, and an agreeable climate. Not all the land on earth is suitable for human habitation under these specifications. Estimates report almost 30% of the land surface is potentially arable; 20% is nonarable mountains; 20% is desert or steppe; 20% is under snow, ice, or permafrost; and 10% lies on soils or regions inadequate for cultivation (Ehrlich, Ehrlich, & Holden, 1973). From the favorable environments of Africa where the human species was born, humans spread to inhabit nearly all the arable lands (Liu, Prugnolle, Manica, & Balloux, 2006). Culture enables humans to adapt to these biophysical elements within the environment and ensures human survival.
Besides being able to bring change and adapt, humans create. Just as we have created the tangible idea of culture, we create other things we cannot see. Steiner (2002) quotes the Chinese American geographer Yi-Fu Tuan as follows:
Humans not only submit and adapt [to change]; they transform in accordance with a preconceived plan. That is, before transforming, they do something extraordinary, namely, “see” what is not there. Seeing what is not there lies at the foundation for all human culture. (p. 35)
The preconceived plan Tuan remarks about is a system. Botkin and Keller define a system “as any part of the universe that can be isolated for purposes of observation and study” (as quoted in Steiner, 2002, p. 21). Ecosystems, then, are systems of ecology. Humans are part of ecosystems, because they interact with and within ecology. Culture is a system, and it is the method humans use to transmit ideas and adapt to environments. Culture directs adaptation to any given environment. For example, this explains why, in the same type of environment, humans will utilize different housing styles.
Just as humans will use different housing types for the same environment, there are different ideas of adaptive systems. Unfortunately, some popular ideas of systems conceptualize them as linear, going from point A to point B. Environmentalist Paul Hawken suggests “[changing] linear systems into cyclic systems,” because this “is the way of the world around us” (as quoted in Steiner, 2002, p. 35). Certainly, most systems in nature are cyclic (e.g., water, carbon, and nitrogen cycles); however, not all human systems are cyclic. The sheer abundance of the American frontier shaped American culture toward consuming resources with the belief they were inexhaustible. Cities grew at unprecedented rates while resources were consumed wastefully, and soon foreign resources were sought to continue the trend (Chen, Coa, & Liu, 2007). The American frontier idea is a linear system that provides end results quickly but in an unsustainable way; that is, linear systems have a beginning and an end; they will end when they have used up all available resources. Energy is expended in linear systems. An easy example of a linear system is the path of most Western products.
Products are manufactured, used, then dumped into the ground and never used again; there is a beginning and an end. In cyclic systems, there is no beginning or end, and nearly the same amount of energy sustains the cycle, as long as conditions permit. When Western products are used in a cyclic system, they are recycled instead of being dumped. Now the product is manufactured, used, and then recycled into the beginnings of another product, which will be manufactured, used, and recycled into the beginnings of another product. In the linear system, energy spent burying discarded products could have been channeled into converting discarded products into raw materials to make new products; instead, energy is used to bury old products, and more energy is needed to produce raw materials for new products. So, a linear system requires fresh input to start it each time; cyclic systems harness initial inputs to continue indefinitely. Cultures exhibit these same system characteristics.
There are many types of systems within a culture. These systems are manifested within a culture’s technology, sociology, and ideology. Technology is usually a physical system, meaning it is a tangible system. Forts, weapons, irrigators, shovels, and the wheel are all manifestations of a technological system. Sociological systems are also tangible and mainly affect social organization at individual and collective levels. Individual, family, and political organization are displays of sociological systems. Ideological systems are intangible systems that affect both technological and sociological systems. These ideologies are contained within myths, beliefs, and knowledge (White, 1949).
In other words, technological and sociological systems are physical representations of the ideological systems held by any particular culture. Each system has influence over the other two systems, and the interaction of these three systems allows cultures to evolve. These systems are very interesting, because they shape tangible representations of people. Kinship organization displays a system’s tangibility and intangibility best. Due to certain ideals held by particular cultures, kinships are arranged differently. Indeed, kinship relationships to mothers and fathers are arranged differently across the world, because people live and think differently. Therefore, intangible ideas shape tangible kinship ties (and vice versa for that matter). But before any system—human or not—can begin, it needs a push; a source of energy.
All energy originates from the sun; consequently, all organisms are governed by thermodynamics. Thermodynamics is the study of how energy converts from heat to mechanical motion. The first law of thermodynamics states energy is neither created nor destroyed; it only passes through different entities (Ehrlich et al., 1973). At the same time, earth’s forces are always moving toward equilibrium by way of depleting all energy, or radiation, from its matter (Watson & Watson, 1972). The second law of thermodynamics states that in each energy transfer there is a loss of usable energy. This law is true for our consumption of foods as well as plants’ conversion of sunlight into energy. During photosynthesis, only 1% or less of sunlight is transferred into usable energy by plants (Ehrlich et al., 1973). The trophic pyramid reflects this energy loss during transfers; its bottom is larger than its top. If energy was not lost during transfers, the trophic pyramid would instead be a trophic square; all initial energy entered into the bottom would be passed to the upper trophic levels. Indeed, energy is always in motion and moving toward being released or dissipated. Humans are one of many organisms trying to capture energy.
Anthropologist Leslie White succinctly states, “All life is a struggle for free energy” (1949, p. 367). Indeed, life contradicts the rest of the cosmos, because it seeks to collect escaping energy. Life attempts to retain as much energy in each transfer as possible. As time passes, humans have become more adept at collecting free energy. White argues human culture evolves with its increasing efficiency to collect energy. He outlines a formula devising this rate of cultural evolution. This formula is based on the amount of harnessed energy per capita or the increase of efficiency in capturing this energy. Indeed, cultural achievements were greatest near periods of markedly increased energy yields, such as during the Agricultural and Industrial Revolutions (White, 1949). Cultures evolved by harvesting energy from their environments, but to do this, humans also derive energy from outside the trophic pyramid.
Energy for human technology comes from natural resources, but its extraction and use is related to time, economics, and scale of demand (Levine et al., 1975). For example, coal mining was scarce before the 19th century because there was little demand for coal. As the Industrial Revolution gained momentum, the demand for coal rose and became an influential part of the economy. During the initial period of increased demand, coal mining technology was crude, and so, extraction and transportation was slow. As the demand for coal grew, it became an even bigger driving force of the economy. As advances in technology increased over time, more coal was made available faster. As time continued and technology gave access to cheaper and more efficient fuels, coal became less and less in demand. Nowadays, some coal is extracted by mountaintop removal, which is more efficient than coal mining was: It employs fewer workers, requires less time, and gains access to smaller coal seams. This example exemplifies how time, economics, and demand influence the extraction of natural resources. However, this extraction technique comes at an environmental cost. Erosion, flooding, and loss of wildlife habitat occur from these extraction techniques. Pollution is another environmental cost.
Pollution is everywhere in the environment. Some of it occurs naturally, such as air pollution from lightning-caused forest fires and volcanic eruptions, while some of it is produced by humans, such as noise pollution from human activities and air pollution from automobiles. There are two types of pollutants: qualitative and quantitative. Qualitative pollutants are synthetic substances introduced by humans, such as DDT, PCBs, industrial chemicals, and herbicides. These substances are usually not biodegradable, and they remain in the environment for decades. Qualitative pollutants do not lose potency during energy transfers and grow more concentrated within organisms as they travel up the trophic pyramid. For example, there are 10,000 aquatic plants supporting 1,000 salmon and 100 eagles in a trophic pyramid. If each aquatic plant has 1 part DDT and each salmon eats 10 aquatic plants, then each salmon has 10 parts of DDT in it. When eagles eat 10 salmon each, each eagle has 100 parts of DDT in it. So, 10,000 parts of DDT become concentrated in 100 eagles.
Quantitative pollutants occur naturally, but they become pollutants as their amounts within the environment are increased by humans. Nitrogen in fertilizers and carbon emitted from combustible engines are quantitative pollutants, because they add to natural levels of nitrogen and carbon already in the environment (Ehrlich et al., 1973). Heat is a quantitative pollutant that humans have drastically increased within the environment. It is the main pollutant from every extraction, conversion, and use of human energy sources (Ehrlich et al., 1973). However, the effect of some pollution is diluted throughout an ecosystem by species diversity.
Ecosystems stay healthy through organism diversity. The more species in an ecosystem, the better, because these inhabitants help disperse energy throughout the ecosystem. If an ecosystem loses one species, another species will fill the resulting empty niche and continue the flow of energy (Ehrlich et al., 1973). This energy flow allows food webs to evolve, and food webs allow environmental change, because energy and nutrients can follow diverse courses before returning back to the environment; subsequently, the course of energy can be different each time (Sargent, 1983). A stable ecosystem grows through complex species diversity, which allows energy different avenues through which to flow. When energy cannot follow different paths, it has the possibility to be cut off. Humans drastically change ecosystems’ species composition, replacing complex stable ecosystems with simple unstable ecosystems through modern agriculture (Ehrlich et al., 1973). However, Meso-American maize agriculture is seen as a stable ecological system, because farmers plant a wide range of maize, such as modern hybrid maize and traditional strains; their focus on maintaining a healthy environment is evident in their culture.
Brush and Perales (2007) conducted a study about what maize type certain ethnic groups chose to plant, where they planted it, and why they planted it. Their research was collected within the state of Chiapas in southern Mexico across different environments and social groups. Brush and Perales found maize diversity was not randomly distributed but rather was a function of biophysical factors, such as altitude and maize species, and socioeconomic factors, such as whether the farmers were mestizo or indigenous and what the economics of their community were. Because mestizo and indigenous people are different in language, ethnolinguistic communities shape the maize landscape, and altitude shapes where ethnolinguistic groups reside. Most indigenous people choose to live at altitudes higher than 1,400 meters above sea level, while mestizos favor lower altitudes, because they evolved from European and indigenous people. Europeans interested in better crop yields favored the lower, flatter areas for cultivation, leaving indigenous groups to higher and more mountainous fields.
But even with these cultural preferences, both ethnicities are found at all elevations. This dispersion affects where particular maize species are grown. Higher than 1,400 meters, maize is grown in a very natural way in small patches among other crops using little commercial input; this method yields less than 1,500 kilograms per hectare of maize. This high-altitude strategy is mostly for subsistence. Conversely, in altitudes below 1,400 meters, and increasingly below 900 meters, maize is grown commercially using large single-crop fields with commercial inputs; this method yields more than 2,000 kilograms per hectare.
At all altitudes, mestizo farmers are geared more toward commercial agriculture than indigenous farmers. At lower altitudes, there is more maize diversity, because farmers must grow nontraditional crops for commercial export while also growing traditional crops. White grain maize is favored by low-altitude farmers for its commercial value. Traditional maize strains are found at all altitudes, while modern strains are only at lower altitudes. Both mestizo and indigenous people plant a variety of maize throughout all altitude levels, although mestizo farmers will try to change their maize seeds and promote gene flow between traditional and modern maize strains.
Maize color is the utmost classifying factor for all farmers. White maize appears only in lower altitudes, while yellow maize is dominant for both mestizo and indigenous farmers. Indigenous farmers favor other maize colors rather than white and yellow, possibly because minor maize colors are associated with indigenous rituals throughout Mexico. Since most commercial growers are mestizo and farm at lower altitudes, they plant white maize, because their buyers prefer white maize. Farmers at lower elevations import modern seed from outside sources, while farmers at higher elevations restock seed banks from the community. Mestizo growers employ a more linear system of energy (it cannot support itself), whereas indigenous farmers obtain their seed directly from their last crop (a circular system).
Between the two farmer groups, Brush and Perales (2007) found three possible differences in maize management: environmental factors, socioeconomic factors, and cultural knowledge. They found mestizo and indigenous farmers live in different ecological niches across each altitude range, and their management choices are inspired by the environment, but not determined by it. Because similar strains of maize are found across all elevations on both mestizo and indigenous farms, the environments in which the two types of farmers farm cannot be very different from one another. This argument suggests environmental differences are minor within a particular altitude range and not the main reason influencing different avenues of maize production within a particular elevation.
Socioeconomic factors such as education, farm size, and access to credit may restrict indigenous farmers from entering the commercial market in areas where both ethnic groups live in lower altitudes. But, this does not explain why farmers at higher altitudes grow maize only for subsistence. Cultural differences are not very significant either, but they provide the best explanation for the contrast in maize management: Indigenous people acquire seeds from within the community, which supports local knowledge and social networks, whereas mestizo farmers do not. Indigenous culture is geared toward crop diversity and a more stable ecosystem, while lower-elevation mestizos are geared toward homogenous commercial crops. These planting practices are mostly a result of cultural attitudes and choices simultaneously affecting and being affected by socioeconomic as well as environmental factors. Indeed, this study aims to clarify relationships between humans and their environment.
All these explanations influence one another. Environmental constraints influence socioeconomics, which, in turn, influence cultural attitudes. These cultural attitudes represent adaptive strategies toward the environment, which is in turn being shaped by cultural attitudes. Understanding these relationships is a key step in human ecology.
Whether humans realize it or not, they affect the earth with nearly every action they perform. Human action can either be directed toward preserving earth’s systems or destroying them. As much as humans want to believe it, “a long history of growth does not imply a long future” (Ehrlich et al., 1973, p. 10). There are several factors that will ultimately affect whether the earth collapses or continues as an appropriate environment for humans. A major factor is overpopulation.
Momentum is the gathering speed behind population growth. Momentum is propelled by the number of females in a population at child-bearing age combined with the number of females who have yet to reach child-bearing age, because both female groups have the potential to increase population growth for another generation. Momentum fosters economic growth and technological advancements, intensifying production of natural resources; this exerts more pressure upon resources.
The delay between cause and effect adds pressure to environments too. Time between an occurrence and its effects may mislead some into believing there was no injury or the problem was solved, postponing necessary action needed to correct problems (Ehrlich et al., 1973). When dealing with population growth, understanding momentum and time lag are crucial.
However, the world’s overpopulation problem is not just one problem; therefore, it requires more than one solution. Humans need to reduce consumption, reduce and improve technological impacts on the environment, and slow or stop population growth (Ehrlich et al., 1973). Just as population can grow exponentially, so can population problems. The larger a population, the more quickly it will grow and develop more problems. Following this trend, humans’ ability to address increasing problems diminishes, because there are more people to be governed by less responsive governors. The most feasible options are lost to humans the longer they wait. Time lag can delay notice of a problem, and the time it takes to fix a problem grows longer with increased population growth (Ehrlich et al., 1973).
Population growth is mostly controlled by birth and death rates. Birth rates are expressed as babies born per 1,000 people per year. To calculate birth rate, the total number of births for the year is divided by the estimated population at the midpoint of that year. For example, the birth rate for Argentina in 2007 was 19 births per 1,000 people. Death rates are calculated the same way as birth rates except without midpoint growth estimation. In 2007, Argentina’s death rate was 8 deaths per 1,000 people (Population Reference Bureau, 2009). Natural population growth is calculated using the difference between birth and death rates divided by the total population and recorded as per hundred (Ehrlich et al., 1973). Therefore, Argentina’s natural growth rate was 1.1% for 2007. The actual population growth rate accounts for immigration and emigration.
Before modern times, population growth was mainly controlled by death rates. Where population increases occurred throughout history, it is because of lower death rates, not increased birth rates. The first big drop in death rates was during the Agricultural Revolution, and this was also the first demographic transition. During this time, people turned their attention from food gathering toward food cultivation, and this made more food available to everyone year round. This change in food production freed people from gathering food, because enough food to feed an entire village could be grown by fewer people. The newly acquired leisure time was directed toward bettering every aspect of human life, which further lowered death rates (Ehrlich et al., 1973). As technology bettered life through industry, agriculture, medicine, sanitation, and transportation, the death rate dropped even further and allowed populations to grow. As long as the environment would allow it, most people on earth had high birth rates and low death rates; however, during the Industrial Revolution, birth and death rates in Western Europe began to decline. This decline was caused by a production shift from agriculture to industry and caused another demographic transition.
In agrarian societies, families encouraged high birth rates, because more children meant more people to help with necessary chores. Hence, children in an agrarian culture are seen as an economic benefit and asset. As industry shifted focus away from agriculture, the need and want for larger families declined, because children in an industrial society are an economic liability. They must be fed, clothed, educated, and kept healthy; these necessities demand large incomes. Children are also consumers and decrease family mobility, which is valued in an industrial society. Children make it harder to gain capital, because they do not usually contribute to income but take away from it. Further hindering birth rates in industrial societies, women and men marry later in life; accordingly, women lose many of their prime reproductive years before marriage, and this further decreases birth rates (Ehrlich et al., 1973).
A third major demographic change occurred after World War II, when major decreases of death rates appeared in underdeveloped countries (UDCs). Death rate decrease in UDCs was caused primarily by better health measures; medicine, drugs, and education about sanitation moved from developed to underdeveloped countries. With better medical knowledge and supplies, UDCs’ death rate decline is in large part due to control of infectious diseases such as malaria, yellow fever, smallpox, and cholera. The death rate decreased most for small children and young adults. Although these health benefits produced a major change in UDCs, this change did not occur within UDCs; it was a function of outside factors, and socioeconomics did not encourage lower birth rates at the same time the death rate dropped. Indeed, these UDCs were not industrialized, so they did not have the same cultural or economic pressures to drop their birth rates. Due to the last major demographic trend, UDCs have a larger base of dependents to support, and this fosters more growth, which further undermines their economic situation (Ehrlich et al., 1973). Zambia is an example of a UDC trying to modernize its socioeconomics using industrial tactics across a large population.
In the late 1950s, the colonial government of Zambia, with the help of the World Bank, built the Kariba Dam on the Middle Zambezi River, and relocated entire Gwembe Tonga villages from their traditional areas. Cliggett, Colson, Hay, Scudder, and Unruh (2007) utilized ethnographic data collected over a span of 50 years with modern satellite imagery to formulate opinions about land cover and the Gwembe people’s land use patterns. Over time, the Gwembe people utilized the environment in the most opportunistic way possible.
In southern Zambia, where the dam is located, farmers are no longer willing to invest in seed or fertilizers, because they know there is high risk of losing their crops. The dam produced this uncertainty. In the 1980s and early 1990s, drought reduced water levels in the reservoir behind the dam, and irrigation became unfeasible, leaving some farmers without water for crops. Conversely, when the lake shrank, fertile land was exposed along the shores for farming. Switching their focus to these newly exposed shore fields, farmers were able to let other fields lie fallow that had been worked constantly since the dam was built.
In the late 1990s and early 2000s, rainfall brought floods and quickly raised the water level of the reservoir. Farmers lost crops, cattle, and farm equipment. Below the dam, fields along the river banks were flooded when floodgates were opened on short notice or no notice at all. These shore fields provide a great resource, but uncertainty makes farming them a high risk operation. Because humans have cleared land for fields, firewood, and building materials, vegetation cover has decreased, allowing flash floods to cause erosion.
War has also brought misery to farmers indirectly. In the 1950s, new roads were built, and credit facilities set up soon after for “seeds, fertilizers and agricultural equipment” (Cliggett et al., 2007, p. 23). The roads allowed farmers to transport their crops to market and receive foreign inputs in the form of fertilizers and pesticides, which produced more crops. However, war in Rhodesia spilled into Zambia and created problems for rural communities. Landmines were strewn across the land, roads were destroyed, and a new structural adjustment curtailed rural economies. Buyers no longer found picking up crops from farms profitable due to deteriorated roads. The poor road conditions also meant inputs were delivered late, if at all. Prices of crops swelled or dropped because of competition with foreign relief grain, and government policies for credit vanished. Some farmers have switched to growing marijuana, because it is profitable, drought resistant, transportable, and requires few inputs. Otherwise, due to production and market uncertainties, farmers invest as minimally as possible in agriculture.
As birth rates are high in the Gwembe region, the arable land available per person is dwindling. People resort to other ventures to generate more income, such as mining, fishing, producing tourist knickknacks, or resettling their entire village where they can farm more profitably. Population pressures increase when prime arable land is given to Europeans or non-Zambians for plantations, crocodile farms, and game ranches for tourists. Whenever there is available land, people will try to make it work until the next opportunity comes along. Fundamentalist Christian churches could bring livelihood changes, because the old Gwembe cult of witchcraft is beginning to be seen as a source of misfortune. These spiritual shifts may alter how people “identify family, mobilize labor, and choose to make a living” (Cliggett et al., 2007, p. 26).
The latest subsistence trend has been to uproot completely, and move to where land is available. Most Gwembe people move to lands near the Kafue National Park because there are benefits of “higher rainfall, better fields, better crops, abundant wood and lots of wild game” (Cliggett et al., 2007, p. 26). These rewards offset the costs imposed by lack of infrastructure, isolation, inadequate water supplies, and threats from wild animals. Overall, mobility has been a primary Gwembe strategy to deal with “environment change, population growth and socio-political dynamics” (Cliggett et al., 2007, p. 27). The only certainty Gwembe people have is uncertainty.
Zambia’s Gwembe Tonga encountered changes in their environmental elements. As the Kariba Dam was not an initial adaptation challenge, the dam is a variable biophysical condition caused by a variable socioeconomic condition: Politics changed to allow the dam. Change in these two environmental conditions initiated changes in other conditions. The dam affected constant biophysical conditions, such as land availability and field access, while also affecting constant socioeconomic conditions of the Gwembe, such as their traditional method of subsistence and social integration.
As seen in Zambia’s example, humans must adapt new sustainable resource management strategies or face collapse. To achieve sustainability, there must be agreement with respect to major goals and how these goals are defined (Sargent, 1983). Developing new technology, easing population pressures, and changing antiquated ideas about humankind’s relationship to the earth are essential goals. However, the balance of sustainability mostly deals with population numbers; if the population gets too large, something must change to accommodate the increase.
Along with increasing their populations, humans have given increased mobility, through advanced technology, to nearly every other organism on the earth: plant, animal, insect, and disease. These organisms hitch a ride on human means of transportation (Park, 1961). As humans continue to impact ecological systems, the connection between these systems and their own well-being is apparent.
An easy step toward achieving sustainability is implementing global recycling. On average, recycling consumes less energy than processing raw materials and saves energy while emitting less pollution; yet, few countries have moved toward encouraging recycling in their economies. Earth’s natural systems sometimes mirror effects produced by humans. For example, the earth’s climate has periodic temperature shifts, making it hard to assess humans’ impact on global temperatures through greenhouse gases. Rapid climatic shifts experienced in modern times are not unlike shifts that occurred naturally between glacial periods, and such shifts make data on human impacts hard to identify (Chen et al., 2007). Even with continued research, only time may reveal humans’ impact with respect to warming the earth.
Human ecology is a science aimed toward the future. Not only does it aim to solve current problems, it seeks to implement new sustainable strategies to balance human systems within environmental systems. If human adaptive strategies continue to lack an emphasis on sustainability, humans may allow looming crises to swell into a global catastrophe. The most pressing of these crises for humans is overpopulation. Due to time lag and momentum, humans will not know they have exceeded the earth’s carrying capacity until it is too late. Humans must address overpopulation immediately to quell growing numbers.
Ehrlich et al. (1973) ask some significant questions about humanity’s future on earth: How long will it take the earth to return to equilibrium after humans exert their final pressure on the carrying capacity? And how many of these pressures on the earth can be alleviated through technology? Indeed, technology paved the way for human comforts and expansion. Will technology continue to alleviate population pressure, allowing the idea of business as usual to continue? Or will change occur within the human mind to stimulate action toward sustainability?
The answers lie in utilizing both approaches, not just one or the other; this tactic has worked splendidly when it has been employed by humans. With it, humans have expanded their environment so much there are no more environments on earth to conquer. Clearly, the human future depends on answering these pressing ecological questions. Human ecology will help ask and answer questions for the future and facilitate strategies to solve ecological problems between humans and their environment, and it will do so through its holistic nature. Human ecology, along with other sciences, can solve life-threatening problems by providing sustainable solutions; only then will humans be an enduring presence on the earth.