Modification of environments and diversification of human societies

 Homo sapiens spread from the African continent and progressively colonized all terrestrial environments. Every human society gradually transformed these environments for its own benefit by adapting their techniques for expliting natural resources.

The impact of Paleolithic hunter-gatherers

The activities of Paleolithic societies had little impact ou plants and animals because human populations were so sparse and relied ou primitive stone tools. Nontheless, these groups undoubtedly contributed to the extinction of certain wild game, such as the mammoth and the European wooly rhinoceros, slow-reproducting species that had been weakened by changed ecological conditions due to climatic variations. Small, isolated populations of endemic mammals, including the hippopotamus and dwarf elephant on the islands in the eastern Mediterranean, met similar fates. Early man prized these animals not only for their meat, but also for their hides, bones, horns, and antlers which provided the raw materials for clothing and tools.

Hunting scene of a Wolly rhino

The effect of fire

Fire, used by early man to flush game from its hiding places, had a freater environmental impact than hunting. This burning encouraged plant species that were resistant to fire and aided the development of savvanas and prairies. The burn technique also may have been used to enhance regrowth of certain edible plantas or to attract grazing animals by regenerating dry prairies, a method used by ranchers today.

Nonetheless, the large quantities of wood coals found in certain prehistoric geological strata remain difficult to interpret. Were the fires that produced them provoked naturally by lighting, or set by man? And in the latter case, were hunters, shepherds, or farmers responsible?

The growth of farming economies

With the appearance of farming 12.000 years ago, the impact of human societies on the environment changed radically since farming involves replacing natural vegetation with plants seeded or bedded by man.

In some cases, the first farming practices preceded the domestication of plants and animals. This was true in the Near East where agriculture was invented by populations that had been sedentary for 2.000 years. Elsewhere, domestication of plants and animals did not necessarily mean the transformation to a farm economy. In Peru, for example, certain nomadic groups continued to live by hunting and gathering even though they farmed a few plants and had domesticated animals.

The hunter-gatherer societies were not all composed of small itinerant groups. Some moved only within a defined territory, while others established permanent homes. Still others had begun to diversfy socially and established hierarchical societies; this was true of the coastal Indians in the American northwest, famous for their "potlathc" art and rituals, who stored acorns in silos and conserved salmon by smoking them.

Generally speaking, the hunter-gatherers were not the societies we imagine, wandering perpetually in search of some pittance and always on the verge os starvation. On the contrary, they had a wealth of natural resources available in their very rich environments, which were then gradually occupied by farming peoples.

The impact of farm practices

The first forms of agriculture had limited impact on the environment. But there can be absolutely no doubt early farming launched a process of environmental change.

Initially, seeds were sacttered directly on the ground, with little soil preparation, particularly in the wooded steppes of the Near East and regions where plant cover was not abundant. But gradually, specialized tools and irrigation techinques were developed.

The fist farmers selected plots that were easy to work, land that could be made fertile through irrigation or which was naturally fertile due to flloding, as in the Nile Valley.

In forested regions, the land had to be cleared withs axes (first made os stone) and fire for planting. This agriculture is often called "itinerant" because these farmers had to abandon their fields regularly and clear others. This is because, after a year or two, the wood ash no longer had any fertilizing effect, and menawhile weeds and natural vegetation invaded and regained control.

But changing fields did not necessarily mean that these farmers moved their homes. After a certain time, the original vegetation flourished again on the abandoned field and it could be recleared. The organic matter produced when the field was left fallow served to regenerate the soil. According to prehistorians, this technique was practiced by the first European farmers, and it is still used today in tropical forests.

However, as populations grew so did their need for additional territory. They were thus forced to clear their old fields before the forest was able to fegenerate itself. Certain species of trees became rare and others simply disappeared. Eventually, only those species belonging to the secondary vegetation, particularly those known as "pioneer" species which require sunlinght to sprout, survived.

Confronted with the need to produce crops regularly, farmers invented techniques making it possible to cultivate the same plots over and over again. Weeding and use of organic fertilizers, often supllied by animal waste, became common practices.

Resource management in early societies.

Each society was thus obliged to organize the agricultural use of its land, to provide for crop rotation and protection of useful tree species. When land was cleared, certain trees were merely pruned. Animal breeders also had to select pasture land where their grazing herds would not damage crops.

Numerous societies utilized live hedges to enclose herds and protect useful tree species. Elsewhere, protection measured led to the development of areas dominated by a single species, such as the karité or palm oil "parks" in Africa. In temperate climes where needs for firewood grew very rapidly, forestry was "rationalized". Oaks, for example, were conserved and the wood reserved for building because the acorns served as food for pigs.

The shaping of contemporary landscapes.

Over time, man's influence spread to increasingly greater areas. This led to a radical transformation of the vegetational cover, which was dominated by cultivated domestic species and self-propagating plants, both adventitious species on farmland and ruderal species around dwellings.

Most contemporary landascapes are influenced in this way by man, and the structure of plant populations is entirely dependant on human activities.

Herds play an important role in this transformation, particularly because they crush and selectively consume new shoots. Overgrazing can have dramatic consequences, because without vegetational cover, the bare soil erodes rapidly, particularly in hilly regions with heavy, seasonal rains.

Development of inhabited areas

Areas reserved for homes increase with the population; population growth in turn increases the needs for natural plant and animal resources. Certain animal species can only are attracted to and subsist on farmlands. Man either relies on this phenomenon to increase his source of wild game, or has to combat the invasion of destructive animals.

In regions of growing population density, certain techniques are used to increase the amount of arable land: in mountainous areas, terraces are built to control water run-off and limit erosion; syampy regions are drained; dry areas are irrigated, etc.

Man eliminates and creates environments that are favorable to certain species, or to certain varieties within a species, as it suits him. In his own territory, he maintains biological diversity if it furnishes things he needs. But elsewhere, in regions far from his own habitat, he does not hesitate to destroy this diversity, exploiting the resources for his own profit, despite the fact other human beings may depend on them.

Storks in a garbage can

Prof. Claudine Friedberg

National Museum of Natural History