[On human longevity--1. external influences]

Human life-span is controlled by many factors, both internal (genomic) and external. In this paper only impact of external conditions is to be discussed. External factors are very variable, sometimes difficult to ascertain, but their control is relatively easier to address than the internal ones. The effect of human activities on human lifespan can be positive or negative. Experimental results have shown that one of the ways leading to prolongation of life-span is caloric restriction (CR). There are, of course, many other factors, not only of nurture character, inflicting on quality and length of human life. Some of them are human products including stress with different levels of inherited ability to resist it, but also possibility to improve individual capacity to control its effect due to hormesis. Prolongation of life expectancy--ageing of the population has become an economic burden in many countries, especially for social and health services.