Nutrition and Diet. Health

Human beings require forty to fifty nutrients to survive and are remarkably omnivorous in design and capable of occupying—and obtaining necessary nutrients from—a wide range of ecological niches. Human design, however, begins with a series of largely irreversible limitations related to primate ancestry in rain forest environments.

Having evolved in an environment with abundant vitamin C, humans are incapable of synthesizing their own. Because human ancestors evolved in an environment rich in steady sources of water, humans are severely limited in their ability to imbibe or store water. Having evolved in an environment relatively poor in sources of sodium, humans crave and store salt.

In addition, for most of human evolution, human ancestors inhabited environments and adopted diets relatively lacking free sugars, although typically rich and varied in other nutrients. Calories, rather than other nutrient needs, were limiting factors in the diet. As a result of both sensory perception (craving) and what was once real need, human dietary choices and food-getting strategies have largely been driven by the search for calories. At the same time human bodies crave and monitor their intake of few other resources, making nutrient quality of food a secondary concern.

The need to obtain sufficient calories for ever- increasing populations from ever-diminishing exploitable areas resulted in the need for human beings to colonize habitats that were less and less favorable, including colder and drier regions and secondary niches among richer environments. Eventually, however, that strategy ran up against increasing circumscription by natural barriers and the competition of other populations.

Population growth combined with circumscription (complicated by natural and cultural modification of existing environments) resulted in a long series of steps in which people increasingly modified their environment to provide increased calories in limited space, often at the expense of other nutrients.

Even before the evolution of modern human beings, refuse and fecal dumps surrounding habitations tended to bring favored plant (and animal) species into proximity of proto-human groups. The smallest and simplest human groups used fire to open landscapes for new growth of preferred vegetable foods and an increase in animal prey populations. Fires started by people may have been responsible for far- reaching conversion of once more-forested environments to open savanna.

Human hunters may also have been responsible in whole or in part (along with post Pleistocene epoch climate changes) for eliminating large game that had theretofore provided major contributions to human diets. Hunter-gatherers are also known to have undertaken a series of less-drastic environmental modifications, such as reseeding exploited resources, fertilizing and protecting them from competition (i.e., weeding), and even irrigating specific locations on a small scale.

The process of economic evolution has been described as the "intensification" of resource exploitation: increasing investment in preparation and modification of natural environments to permit more food to be gathered and ultimately grown on each unit of land but resulting also in the ultimate use of foods that are less and less desirable, a decline in food variety, and therefore a decline in the availability of other nutrients. The intensification took two forms, largely in sequence.

Broad-Spectrum Revolution. First, early hunter-gatherers, relying on large game (for perhaps 40 percent of their diets) and select vegetable resources, gradually broadened the spectrum of resources that they were willing to eat (the so-called broad-spectrum revolution); people ate a variety of more-plentiful but low-priority food that was harder to get and less desirable in terms of the concentration and variety of nutrients it offered. This broadening spectrum of exploitation probably added little to dietary quality because the foods were often of lower quality than those they replaced; and it probably resulted in a decline in the reliability of resources because resources once reserved for emergencies became staples instead.

Second, people increasingly focused on the intensive exploitation, ultimate domestication (farming), and storage of resources, typically cereals and root crops selected for their abilities to provide the most calories per unit of land, not for their palatability or their quality as foods. Farmed foods are commonly of lower quality than foraged ones, and storage itself tends to reduce the availability of vitamins.

Farming techniques involve concentration of one species in a particular region, the increased modification of land to support the increased density of the particular crop, the dispersal of efficiently produced crops to new regions, and the displacement of indigenous wild plants. Farming and associated storage and sedentism (a settled lifestyle) are often thought to increase the reliability of food supplies through human control.

However, increased concentration of individual species, the extension of those species beyond their normal ranges, and the necessity of remaining sedentary through the growth, harvest, and storage cycle, even in the event of poor harvests, may actually have made food supplies less reliable.

The sequence, although increasing efficiency in terms of calories produced per unit of land, seems to have resulted in the declining efficiency of labor (calories produced per hour of work). Estimates of relative efficiency come from an area of study called "optimal foraging theory" (OFT). OFT argues that resources can be ranked in terms of caloric production per unit of labor.

OFT also argues that hunter-gatherers should and generally do follow the sequence of ranking, taking high-ranked resources (i.e., calorie efficient in terms of labor) before taking those of lower rank and turning to the latter only as high-rank resources are depleted. (For a variety of reasons, individual groups may not always follow these rankings; but it is quite clear that on average changing worldwide patterns of human consumption in the last twenty thousand or more years conform to the predictions quite nicely.) People are seeing a sequence of declining labor efficiency through time.

Large game (according to many studies in different parts of the world) is by far the most efficiently exploited wild resource as long as it is available. Small game, fish (unless caught with large nets or weirs), shellfish, and nuts associated with a broadening spectrum of resource use are of lower rank. Small-seeded plants such as grasses (including the ancestors of the major modern staples such as wheat and barley) are among the lowest-ranked—least labor-efficient—resources. Moreover, domestication adds little if any efficiency to their exploitation.

Large-game hunting generally appears to have been more efficient than most prehistoric modes of farming. The implication is that the farming of such crops resulted not from the invention of farming techniques but from the declining availability of preferred resources.

The history of agriculture can, to a large extent, be visualized as an interaction between population density, technology, and increased intensity of farming, including the use of marginal lands, the increasing frequency of cropping on land already farmed, and the accumulation of new tools and techniques.

In its most extensive forms (slash and burn), agriculture involves a ratio of as many as twenty-five or more years of fallow for each year of crop harvest (a 25-30:1 ratio), and therefore works only where population densities are low. The crop is produced largely by burning forest and planting in the ashes. The extended fallow period provides for significant regrowth of secondary if not primary forest before trees are burned again and seeds planted with no further fertilization, the only necessary tool being a digging stick.

A smaller fallow crop ratio, for example, 10-15:1, supporting somewhat larger populations, permits natural recycling to produce only brush that provides less ash when burned, presents more difficult clearing problems, and requires hoeing and supplementary fertilization. A third type of farming involving ratios of only 3-4:1 permits only grasses to regrow, so that burning provides little fertilizer and does little to clear dense grass roots.

Plowing and additional fertilizing become necessary. More-intensive systems associated with high population densities involve cropping three years in four (a 1:3 ratio), requiring extensive tilling or plowing and significant fertilizing. Multicropping (planting several crops per year without fallow) typically relies on irrigation water to support and fertilize plants.