Migration:

Migration, for humans, is the movement of individuals from one place to another and from one population to another. Populations in their home regions have rates of birth, death and resulting population growth or decline. Migrants leave one home population and are expected to arrive in another. While in transit they form distinct migratory populations with their own rates of birth and death, and their own directions. These principles are explained in more detail in the Basic Model.


Population Pyramids:

The simulation of human migration is expressed graphically in population pyramids, and is also portrayed in mathematical equations that are similar to the population pyramids. Here are some introductory points:

Population pyramids show the size, age and sex distribution of populations. They show a census of the population at a moment in time. Females are shown on the left, males are shown on the right, children are shown at the bottom, and old people are shown at the top. In these pyramids, populations are shown in five-year groups: from birth through 4 years, ages 5 to 9, 10 to 14, etc.

Periods of analysis - the processes of birth, death, and migration are analyzed over periods of 5 years. At the end of each 5-year period, we can look at the populations and see the results of these processes.

Births - infants are added at the bottom of the pyramid.

Deaths - people are removed at all levels of the pyramid, especially at the bottom and top.

Migration - people are removed at all levels of some populations (especially young adults), and added into other populations.

Expectation of life at birth (same as average age at death) - reflected in the proportion of old to young persons. It is very close to the average age of persons living.


The Basic Model:

These three simulations of major human migrations are based on a single underlying logic. For Atlantic slave trade, Oriental slave trade, and European migration, parallel processes of movement took place. While the logic of each simulation is explained separately, you may wish to consult this general statement. Summary of the Basic Model