according to wiki.......
Human migration
denotes any movement by humans from one locality to another, sometimes over long distances or in large groups.
Migration (resulting in population isolation) is one of the four evolutionary forces (along with natural selection, genetic drift, and mutation). The discipline of Population genetics is the study of the distribution of and change in gene variation (allele) frequencies under such influences.
The movement of populations in modern times has continued under the form of both voluntary migration within one's region, country, or beyond, and involuntary migration (which includes the slave trade, trafficking in human beings and ethnic cleansing). People who migrate are called migrants, or, more specifically, emigrants, immigrants or settlers, depending on historical setting, circumstances and perspective.
The pressures of human migrations, whether as outright conquest or by slow cultural infiltration and resettlement, have affected the grand epochs in history (e.g. the Decline of the Roman Empire); under the form of colonization, migration has transformed the world (e.g. the prehistoric and historic settlements of Australia and the Americas). Population genetics studied in traditionally settled modern populations have opened a window into the historical patterns of migrations, a technique pioneered by Luigi Luca Cavalli-Sforza.
mtDNA-based chart of large human migrations.
Forced migration (see population transfer) has been a means of social control under authoritarian regimes, yet free initiative migration is a powerful factor in social adjustment (e.g. the growth of urban populations).
In December 2003 The Global Commission on International Migration (GCIM) was launched with the support of Kofi Annan and several countries, with an independent 19-member Commission, threefold mandate and a finite life-span, ending December 2005. Its report, based on regional consultation meetings with stakeholders and scientific reports from leading international migration experts, was published and presented to UN Secretary-General Kofi Annan on 5 October 2005.
