INTRODUCTION

During the past 20,000 years the most striking change in the lifestyle of humans was the transition from the hunter-gatherer culture to the introduction of agriculture and animal husbandry associated with stable settlement in the Neolithic. With sufficient food resources, the human population, which had been scattered, started to grow. Larger urban communities were formed, which was the starting point of culture and technology.

Humans have evolved with bacterial communities (microecological systems) as colonizers (skin, mucosa, gastrointestinal tract) and as conditional pathogens. For true pathogens the more dense human communities became of particular interest, especially for specialization in the human hosts (McKeown, 1988).

The so-called technical revolution that began at the end of the 19th century created a need for energy as a permanent concern. Because of continuing urbanization and the growing human population in the Third World, sustainability of food supply remains an important issue.

When, 200 years ago, a more productive agriculture began that was based on the then-young agricultural sciences, the principle of enduring means of production long endured, especially with regard to recycling of energy. These principles began to fade with the invention of mineral fertilizers, followed by mechanization and energy-consuming (wasting) means of production that were more independent of seasons. By the middle of the last century this had led to a high degree of mechanization of agriculture, where animals and plants were regarded more as “work pieces” than as living beings.