How do populations change over time - Essay Example

Rapid growth in the human population became visible in the year 1810 when the population doubled in a span of a hundred years. Paul Ehrlich a demographer says the world’s population is likely to double to fourteen billion but other demographers say there is a high likelihood that it will not. Population dynamics explains how the world population has been changing over time and how it continues to change; it is not just a matter of numbers. Fertility, mortality and migration are the three big factors that influence demography, and they explain how a region’s population changes over time due to births, deaths and the movement in and out of the place by people.

For example, to calculate the expected population of a certain country in 20 years time: one needs to know the population as at the current year, plus the births in the 20 year period less the deaths in the same period. Add this to the number of people who move into that country less the number of people who move out of the same country at that given period of 20 years (Manza, Haney and Arum 541). These sounds very simple to calculate, but it is important to note that understanding the dynamics of how fertility, mortality and migration affect the population is the key. . In short, demographers observed that in cases where pretransition is characterized by high fertility, the fertility decreases in posttransition.

It has therefore been observed that a country cannot go back to the high fertility rates in pretransition once it has achieved post transition. These are the characteristics of first demographic transition (Manza, Haney and Arum 541). This serves to explain why the demographers did not agree with Ehrlich about the population growth that was expected. There was a population soar in the 20th century due to decline in mortality rate that had not yet been followed by a decline in fertility. This meant that the population expanded very fast and alarmed many demographers as a decline in fertility had not been experienced yet.

It is now being observed that fertility is on the decline in most regions and this explains why the population might never double to 14 billion. Although the developed countries are experiencing a higher decline in fertility s compared to the developing countries, it still is a notable decline in fertility. A good case study example is Sudan whereby there is a very high populace of youths and a low population of old aged people, and it being a poor nation, poverty influences mortality at different ages.

Although mortality has significantly reduced in the nation, child mortality is still very high despite the fact that fertility is still high. Out of the many babies born, many also die and those that survive and graduate to early childhood may still die, therefore, the population of the young is very high, but the old are few, meaning that the life expectancy of Sudan is