The world population reached 7 billion in 2012, which is 6 billion more than in 1800. This remarkable population growth is the result of several factors like advances in the medical, technological and public health systems resulting in the control and treatment of communicable diseases, the control of pandemics, the end of large-scale wars, improvements in living conditions and the revolutions in the field of agriculture. Because of all these factors, there has been a considerable improvement in the life expectancy of human beings. There is also an alarming reduction in fertility rates. The combination of declining fertility rate and augmented life expectancies has led to a change in the demographics of the population with the strata of old...