THe Human Population
...(Wright 2005). Epidemiological transition is a pattern of change in morality factors. We can consider it as the shift from infectious and deficiency diseases to chronic noncommunicable diseases (Wahdan 1996). The epidemiological transition was thought to be a unidirectional process, beginning when infectious diseases were predominant and ending when noncommunicable diseases dominated the causes of death. It is now evident that this transition is more complex and dynamic where health and disease evolve in diverse ways. It is rather a continuous transformation process with some diseases disappearing and other re-emerging (Wahdan 1996). Environmental resistances in an epidemiological transition are many. Biological factors such as adaptive microorganisms and certain practices of modern medicine have played a key role. Such environmental factors like environmental pollutants and over crowding have provided the need for change. Cultural and behavioral factors include changes in lifestyle and over-all decreased moral values (Wahdan 1996). Demographic changes encompass changes of both mortality and fertility. In essence, deaths and births which are represented in thousands as crude birth rates (CBR) and crude death rates (CDR) in order to compare countries regardless of their total size (Wright 2005). The demographic transition is presented as occurring in four phases. PHASE I is the stability resulting from a high crude birth rate (CBR) being offset by a equally high crude death rate (CDR). PHASE II is marked by the declining CDR. This is considered to be the epidemiologic transition. CBR remains high and population growth takes place. PHASE III is marked by a declining CBR due to a decline in fertility rate. Population growth remains constant. PHASE IV is the modern stability is achieved by a continuing low CDR, but an equally low CBR. A stable population only occurs when the CDR and the CBR are equal (Wright 2005). Results tend to concentrate on mortality as they are the best indicators to measure and are random. However, overall mortality does not tell everything about health, so results should also reflect both mortality and morbidity (rate of incidence) (Wahdan 1996). Developed countries have completed the demographic transition in which they have competed Phase IV. However, developing countries are still in Phases II and III (Wright 2005). ...