And,this constant movement of population also affects the humanitarian workers as it makes the planning and the delivery of aid much more difficult because we cannot predict where the people are going or if they are coming back."

VOA: standard.2009.06.21

More specifically, imagine the simplest case of a population of a constant size - say a million (the approximate size of the Holy Land at the time of Jesus).

BBC: Family trees: Tracing the world's ancestor

Mr White said over the past 10 years there had been a constant movement of population from the "Donegal side of the Foyle" to the east bank and other parts of Northern Ireland.

BBC: News - Fears over Protestant exodus from Derry west bank

Israel, like the United States, has struggled to find a way to secure its borders and its population while dealing with a constant stream of immigrants from neighboring countries and, increasingly, the African continent.

FORBES: Israel Forcibly Injected African Immigrants with Birth Control, Report Claims