Populations may be defined in different ways, and changes from one definition to another over time hinder assessments of population growth. There are three types of changes happening in population. The first one is the change in population density, which means more and more people are living in urban areas. The second change is found in population distribution because migration patterns have changed. Regional differences are due to differences both in natural growth (births minus deaths) and in migration patterns. The third one is the change in aging structure as women have less children, which leads to serious aging problem. The structure of the population by gender reveals some possible bias in age reporting. Comparison of male and female temporary migrants by age reveals that it is not uncommon for temporary migrants to be predominately female in the younger age groups. There will be as many old people as young people on this planet.