Ecologists joke that they spend most of their time thinking about food and sex. They must know how organisms feed and reproduce in order to understand the web of relationships within an environment. Habitat, an organism's "address," and niche, its "profession," are fundamental ecological concepts. Paul Colinvaux, professor of zoology at Ohio State University, claims that human history can be interpreted and future events predicted using the ecological theory of niche-space and population pressure. History has been constantly reinterpreted and rewritten, and Colinvaux's novel explanation may not be accepted by all, but it makes for a provocative and highly readable book.

Human "breeding strategy" has not changed since the Ice Age, says Colinvaux, and every couple seeks the optimum number of children for its situation. The result is ever-increasing numbers, relieved only by new technology-created niche-space (irrigation, for example, enabling a desert to produce crops) or by emigration or war. All populations tend to expand to the limit of the resources available, and human populations have been kept stationary only by cultural devices such as rigid taboos. Even hope will raise the numbers of children chosen.

"The new hope may reflect some simple influx of new resources, such as the fruits of conquest or green-revolution food, or it may rest on no more than learning that improvements are possible in theory. A feeling of well-being makes the numbers rise," writes the author.

The resulting population pressure Leads, he says, to "a predictable series of events which include trade, colonialism, class repression and aggressive war. Since our own numbers will continue to grow, it is inevitable that our own future holds variants on these themes."

Colinvaux supports his theory with vivid acounts of historic trends and crucial battles. Alexander united the Greeks and conquered much of Asia because the Greeks were crowded in their already-eroded land. Similar pressures motivated the Romans and Carthaginians, and also pushed desert warriors under the banner of militant Islam across Asia and North Africa into Spain. He compares the horse-archers of Genghis Khan to "human lemmings" and examines the mix of environmental stimuli that caused cycles of nomad invasions ("Armed emigration from an overcrowded habitat") into Eastern Europe -- Scythians, Sarmatians, Huns, Magyars, Mongols. He similarly examines the "rebellion in America" and the "Manifest Destiny" to conquer a continent, prompted by the realization that "the way of life, the niche, found to be so satisfactory for England was not so appropriate to Englishmen in America. . . . Why be master and man when there was room for everybody to be master?" Today, he sees parallels between the United States and late Imperial Rome: "Spreading bureaucracy, restraint on individual freedom to do as you please, welfare and cheap intertainment for people who must live in large cities, inflation, and wage and price controls." Finally, in colorful capsule histories, he examines the modern wars of Sweden, France, Germany, Japan and England, as each in turn sought to widen its sphere (what Hitler called the German need for "living space") and maintain its niche in the face of the pressure of a burgeoning population.

Colinvaux dismisses conventional wisdom about current population trends, though he supplies no data. "It is essential to realize that people of poor countries have their large families from choice. . . . Providing the poor with birth-control devices will not result in fewer children." "There is no evidence that making people wealthy will halt population growth." Nor is the current growth due to the medical advances ("death control before birth control"). Finally, he rejects the argument that the rate of human growth may be starting to inflect or level off.

Colinvaux boldly follows his theory where it heads, and speculates about "The Shape of Things to Come." The ecological hypothesis predicts, therefore, that there can be no war of aggression which involves a clear attack by either the United States or the Soviet Union on the other," since both countries have sufficient niche-space and internal opportunities for their people. He sees Western prosperity built on the "slaves" of fossil fuel, but "present (1980) prices are still absurdly low by the norms 10 years from now. Oil, and then coal, will soon be so expensive that nuclear reactors will seem economical to run." U.S. farming, built on the use of chemical fertilizers, will also be affected, and "cheap food too has gone forever." He envisages nuclear weapons employed by island powers "forced by niche and breeding strategy to that same sequence of success; liberty, rising numbers again. This is a progress that leads to the need to fight; indeed, to attack." He sees an eventual erosion of freedom, at least in America: "Liberty, in the Jeffersonian sense, cannot survive a continual packing-in of people." But he imagines a future time when the resources in land permit "more real liberty . . . in the Soviet Union than there is in the West." He sees continual armed conflict in Africa and Latin America, makes a comparison between Idi Amin and Peter the Great, says India and China "have real need" of nuclear weapons, and speculates on which have the better chance for survival -- missiles launched from the MX race-track.

Pretty far afield from biology, but nonetheless a stimulating hypothesis from a lively mind.