Born Expecting the Pleistocene
by Mark Seely
Not our natural habitat
The mismatch hypothesis
Our bodies including our brains—and thus our behavioral predispositions—have evolved in response to very specific environmental and social conditions. Many of those environmental and social conditions no longer exist for most of us. Our physiology and our psychology, all of our instincts and in-born social tendencies, are based on life in small semi-nomadic tribal groups of rarely more than 50 people. There is a dramatic mismatch between life in a crowded, frenetic, technology-based global civilization and the kind of life our biology and our psychology expects .
And we suffer serious negative consequences of this mismatch. A clear example can be seen in the obesity epidemic that has swept through developed nations in recent decades: our bodies evolved to meet energy demands in circumstances where the presence of food was less predictable and periods of abundance more variable. Because of this, we have a preference for calorie-dense food, we have a tendency to eat far more than we need, and our bodies are quick to hoard extra calories in the form of body fat.
This approach works quite well during a Pleistocene ice age, but it is maladaptive in our present food-saturated society—and so we have an obesity epidemic because of the mismatch between the current situation and our evolution-derived behavioral propensities with respect to food. Studies on Australian aborigines conducted in the 1980s, evaluating the health effects of the transition from traditional hunter-gatherer lifestyle to urban living, found clear evidence of the health advantages associated with a lifestyle consistent with our biological design . More recent research on the increasingly popular Paleo-diet  has since confirmed wide-ranging health benefits associated with selecting food from a pre-agriculture menu, including cancer resistance, reduction in the prevalence of autoimmune disease, and improved mental health.
 Ornstein, R. & Ehrlich, P. (1989). New World, New Mind. New York: Simon & Schuster.
 O’Dea, K., Spargo, R., & Akerman, K. (1980). The effect of transition from traditional to urban life-style on the insulin secretory response in Australian Aborigines. Diabetes Care, 3(1), 31-37; O’Dea, K., White, N., & Sinclair, A. (1988). An investigation of nutrition-relatedrisk factors in an isolated Aboriginal community in northern Australia: advantagesof a traditionally-orientated life-style. The Medical Journal of Australia, 148 (4), 177-80.
 E.g., Frassetto, L. A., Schloetter, M., Mietus-Snyder, M., Morris, R. C., & Sebastian, A. (2009). Metabolic and physiological improvements from consuming a Paleolithic, hunter-gatherer type diet. European Journal of Clinical Nutrition, 63, 947=955.
The mechanisms of cultural evolution can be seen in the changing patterns of foraging behavior in response to changes in food availability and changes in population density. Archaeological analyses suggest that there is a predictable pattern of dietary choice that emerges from the interaction among population density, relative abundance of preferred food sources, and factors that relate to the search and handling of various foods.  In general, diets become more varied, or broaden, as population increases and the preferred food becomes more difficult to obtain. When a preferred food source is abundant, the calories in the diet may consist largely of that one particular food. But as the food source becomes more difficult to obtain, less preferable foods will be included and the diet will broaden. Such dietary changes imply changes in patterns of behavior within the community—changes of culture.
Behavior ecologists and anthropologists have partitioned the foraging process into two components with respect to the cost-benefit analysis associated with dietary decisions:
search and handling.  The search component of the cost-benefit ledger refers to the amount of work per calorie payoff (and other benefits such as the potential for enhanced social standing) associated with a food item’s abundance, distance, terrain, proximity of another group’s territory, water sources, etc. The handling component refers to the work per calorie payoff associated with getting the food into a state (location, form, etc.) in which it can be consumed. Search and handling considerations can be largely independent of each other. The residential permanence involved with the incorporation of agriculture reduces the search consideration greatly, and makes handling the primary consideration. Global industrial food economies change entirely the nature of both search and handling: handling in industrial society—from the perspective of the individual and the individual’s decision processes—is reduced largely to considerations of speed and convenience. The search component has been re-appropriated and refocused by corporate marketing, and reduced to something called shopping.
Domestication, hands down the most dramatic and far-reaching example of cultural evolution, emerges originally as a response to scarcity that is tied to a lack of mobility and an increase in population density. Domestication is a way of further broadening the diet when other local sources of food are already being maximally exploited. Initial experimentation with animal domestication “occurred in situations where forager diets were already quite broad and where the principle goal of domestication was the production of milk, an exercise that made otherwise unusable plants or plant parts available for human consumption. . . .”  The transition to life-ways based even partially on domestication has some counter-intuitive technological ramifications as well.
This leads to a further point about efficiency. It is often said that the adoption of more expensive subsistence technology marks an improvement in this aspect of food procurement: better tools make the process more efficient. This is true in the sense that such technology often enables its users to extract more nutrients per unit weight of resource processed or area of land harvested. If, on the other hand, the key criterion is the cost/benefit ratio, the rate of nutrient gained relative to the effort needed to acquire it, then the use of more expensive tools will often be associated with declines in subsistence efficiency. Increased investment in handling associated with the use of high-cost projectile weapons, in plant foods that require extensive tech-related processing, and in more intensive agriculture all illustrate this point. 
In modern times, thanks to the advent of—and supportive propaganda associated with—factory industrial agriculture, farming is coupled with ideas of plentitude and caloric abundance. However, in the absence of fossil energy and petroleum-based chemical fortification, farming is expensive in terms of the calories produced as a function of the amount of work involved. For example, “farmers grinding corn with hand-held stone tools can earn no more than about 1800 kcal per hour of total effort devoted to farming, and this from the least expensive cultivation technique.”  A successful fishing or bison hunting expedition is orders of magnitude more efficient in terms of the ratio of calories expended to calories obtained.
 Bird & O’Connell [Bird, D. W., & O’Connell, J. F. (2006). Behavioral ecology and archaeology. Journal of Archaeological Research, 14, 143-188]
 Ibid, p. 152.
 Ibid, p. 153.
 Ibid, p. 151, italics in original.
The birth of the machine
The domestication frame
The Neolithic marks the beginnings of large scale domestication, what is typically referred to as the agricultural revolution. It was not really a revolution in that it occurred over an extended period of time (several thousand years) and in a mosaic piecemeal fashion, both in terms of the adoption of specific agrarian practices and in terms of specific groups of people who practiced them. Foraging lifestyles continue today, and represented the dominant lifestyle on the planet until relatively recently. The agricultural revolution was a true revolution, however, in terms of its consequences for the humans who adopted domestication-based life-ways, and for the rest of the natural world. The transition from nomadic and seminomadic hunting and gathering to sedentary agriculture is the most significant chapter in the chronicle of the human species. But it is clearly not a story of unmitigated success. Jared Diamond, who acknowledges somewhat the self-negating double-edge of technological “progress,” has called domestication the biggest mistake humans ever made.
That transition from hunting and gathering to agriculture is generally considered a decisive step in our progress, when we at last acquired the stable food supply and leisure time prerequisite to the great accomplishments of modern civilization. In fact, careful examination of that transition suggests another conclusion: for most people the transition brought infectious disease, malnutrition, and a shorter lifespan. For human society in general it worsened the relative lot of women and introduced class-based inequality. More than any other milestone along the path from chimpanzeehood to humanity, agriculture inextricably combines causes of our rise and our fall. 
The agricultural revolution had profoundly negative consequences for human physical,
psychological, and social well being, as well as a wide-ranging negative impact on the planet.
For humans, malnutrition and the emergence of infectious disease are the most salient physiological results of an agrarian lifestyle. A large variety of foodstuffs and the inclusion of a substantial amount of meat make malnutrition an unlikely problem for hunter gatherers, even during times of relative food scarcity. Once the diet is based on a few select mono-cropped grains supplemented by milk and meat from nutritionally-inferior domesticated animals, the stage is set for nutritional deficit. As a result, humans are not as tall or broad in stature today as they were 25,000 years ago; and the mean age of death is lower today as well.  In addition, both the sedentism and population density associated with agriculture create the preconditions for degenerative and infectious disease. “Among the human diseases directly attributable to our sedentary lives in villages and cities are heart and vascular disorders, diabetes, stroke, emphysema,
hypertension, and cirrhoses [sic.] of the liver, which together cause 75 percent of the deaths in the industrial nations.”  The diet and activity level of a foraging lifestyle serve as a potent prophylactic against all of these common modern-day afflictions. Nomadic hunter-gatherers are by no means immune to parasitic infection and disease. But the spread of disease is greatly limited by low population density and by a regular change of habitation which reduced exposure to accumulated wastes. Both hunter-gatherers and agriculturalists are susceptible to zoonotic diseases carried by animals, but domestication reduces an animal’s natural immunity to disease and infection, creates crowded conditions that support the spread of disease among animal populations, and increases the opportunity for transmission to humans. In addition, permanent dwellings provide a niche for a new kind of disease-carrying animal specialized for symbiotic parasitic cohabitation with humans, the rat being among the most infamous.
Plagues and epidemic outbreaks were not a problem in the Pleistocene.
There is a significant psychological dimension to the agricultural revolution as well.
A foraging hunter-gatherer lifestyle frames natural systems in terms of symbiosis and interrelationship. Understanding subtle connections among plants, animals, geography,
and seasonal climate change is an important requisite of survival. Human agents are intimately bound to these natural systems and contemplate themselves in terms of these systems, drawing easy analogy between themselves and the natural communities around them, using animals, plants, and other natural phenomena as metaphor. The manipulative focus of domestication frames natural systems in antagonistic terms of control and resistance. “Agriculture removed the means by which men [sic.] could contemplate themselves in any other than terms of themselves (or machines). It reflected back upon nature an image of human conflict and competition . . . .”  The domestication frame changed our perceived relationship with the natural world,
and lies at the heart of our modern-day environmental woes. According to Paul Shepard,
with animal domestication we lost contact with an essential component of our human nature, the “otherness within,” that part of ourselves that grounds us to the rest of nature:
The transformation of animals through domestication was the first step in remaking them into subordinate images of ourselves—altering them to fit human modes and purposes. Our perception of not only ourselves but also of the whole of animal life was subverted, for we mistook the purpose of those few domesticates as the purpose of all. Plants never had for us the same heightened symbolic representation of purpose itself. Once we had turned animals into the means of power among ourselves and over the rest of nature, their uses made possible the economy of husbandry that would, with the addition of the agrarian impulse, produce those motives and designs on the earth contrary to respecting it. Animals would become “The Others.” Purposes of their own were not allowable, not even comprehensible. 
Domestication had a profound impact on human psychological development. Development—both physiological and psychological—is organized around a series of stages and punctuated by critical periods, windows of time in which the development and functional integration of specific systems are dependent upon external input of a designated type and quality. If the necessary environmental input for a given system is absent or of a sufficiently reduced quality, the system does not mature appropriately. This can have a snowball effect because the future development of other systems is almost always critically dependent on the successful maturation of previously developed systems. The change in focus toward the natural world along with the emergence of a new kind of social order interfered with epigenetic programs that evolved to anticipate the environmental input associated with a foraging lifestyle. The result was arrested development and a culture-wide immaturity:
Politically, agriculture required a society composed of members with the acumen of children. Empirically, it set about amputating and replacing certain signals and experiences central to early epigenesis. Agriculture not only infantilized animals by domestication, but exploited the infantile human traits of normal individual neoteny. The obedience demanded by the organization necessary for anything larger than the earliest village life, associated with the rise of a military caste, is essentially juvenile and submissive . . . . 
 Diamond (1992), p. 139. [Diamond, J. (1992). The Third Chimpanzee. New York: HarperCollins.]
 Shepard (1998) [Shepard, P. (1998). Coming Home to the Pleistocene. Washington, D.C.: Island Press]
 Ibid, p. 99.
 Shepard (1982), p. 114. [Shepard, P. (1982). Nature and Madness. Athens Georgia: University of Georgia Press]
 Shepard (1998), p. 128.
 Shepard (1982), pp. 113-114.