Human migration

"Human migration" denotes any movement by humans from one locality to another (migration), often over long distances or in large groups. Humans are known to have migrated extensively throughout history and prehistory.
Migration and population isolation is one of the four evolutionary forces (along with natural selection, genetic drift, and mutation). The study of the distribution of and change in allele (gene variations) frequencies under such influences is the discipline of Population genetics.

Different types of migration include:
*Daily human commuting.
*Seasonal human migration is mainly related to agriculture.
*Permanent migration, for the purposes of permanent or long-term stays.
*Local
*Regional
*Rural to Urban, more common in developing countries as industrialization takes effect
*Urban to Rural, more common in developed countries due to a higher cost of urban living
*International

Human migration has taken place at all times and in the greatest variety of circumstances. It has been tribal, national, class and individual. Its causes have been climatic, political, economic, religious, or mere love of adventure. Its causes and results are fundamental for the study of ethnology, of political and social history, and of political economy.


Pre-modern migrations

Historical migration of human populations begins with the movement of Homo erectus out of Africa across Eurasia about a million years ago. Homo sapiens appears to have colonised all of Africa about 150 millennia ago, moved out of Africa some 80 millennia ago, and spread across Eurasia and to Australia before 40 millennia ago. Migration to the Americas took place about 20 to 15 millennia ago, and by 2 millennia ago, most of the Pacific Islands were colonised. Later population movements notably include the Neolithic revolution, Indo-European expansion, and the Early Medieval Great Migrations including Turkic expansion. The Age of Exploration and European Colonialism led to an accelerated pace of migration since Early Modern times.


Modern migrations

Industrialization
While the pace of migration had accelerated since the 18th century already (including the involuntary slave trade), it would increase further in the 19th century. Manning distinguishes three major types of migration: labour migration, refugee migrations and lastly: urbanization. Millions of agricultural workers left the countryside and moved to the cities causing unprecedented levels of urbanization. This phenomenon began in Britain in the late 18th century and spread around the world and continues to this day in many areas.
Industrialization encouraged migration wherever it appeared. The increasingly global economy globalised the labour market. Atlantic slave trade diminished sharply after 1820, which gave rise to self-bound contract labour migration from Europe and Asia to plantations. Also overpopulation, open agricultural frontiers and rising industrial centres attracked voluntary, encouraged and sometimes coerced migration. Moreover, migration was significantly eased by improved transportation techniques.
Between 1846 and 1940 mass migrations occurred world wide. The size and speed of transnational migratory movements were unprecedented. Some 55 millions of migrants moved from Europe to America, and an additional 2,5 million moved from Asia to America. Of this transatlantic migrations, 65% went to the United States. Other major receiving countries were Argentina, Canada, Brazil and Cuba. (see also Immigration to the United States, Italian diaspora, Irish diaspora etc.)
During this same period similar large numbers of people migrated over large distances within Asia. Southeastern Asia received 50 million migrants, mainly from India and south China. North Asia, that be Manchuria, Siberia, Central Asia and Japan together, received another 50 million. A movement that started in the 1890's with migrants from China, Russia and Korea, and was especially large due to coerced migration from the Soviet Union and Japan in the 1930s. Less is known about exact numbers of the migrations from and within Africa in this period, but Africa experienced a small nett immigration between 1850 and 1950, from a variety of originins.
Transnational labour migration reached a peak of three million migrants per year in the early twentieth century. Italy, Norway, Ireland and the Quongdong region of China were regions with especially high emigration rates during these years. This large migration flows influenced the process of nation state formation in many ways. Immigration restrictions have been developed, as well as diaspora cultures and myths that reflect the importance of migration to the foundation of certain nations, like the American melting pot. The transnational labour migration fell to a lower level from 1930s to the 1960s and then rebounded.
The twentieth century experienced also an increase in migratory flows caused by war and politics. Muslims moved from the Balkan to Turkey, while Christians moved the other way, during the collapse of the Ottoman Empire. 400.000 Jews moved to Palestine in the early twentieth century. The Russian Revolution of 1917 caused some 3 million Russians, Poles and Germans to migrate out of the Soviet Union. World War II and decolonization also caused migrations, see below.

World War II
The Jewish diaspora across Europe, the Mediterranean and the Middle East formed from voluntary migrations, enslavement, threats of enslavement and pogroms. After the Nazis brought the Holocaust upon Jewish people in the 1940s, there was increased migration to the British Mandate of Palestine, which became the modern day state of Israel as a result of the 1947 UN Partition Plan.
Provisions of the Potsdam Agreement from 1945 signed by victorious Western Allies and the Soviet Union led to one of the largest European migrations, and definitely the largest in the 20th century. It involved the migration and resettlement of close to or over 20 million people. The largest affected group were 16.5 million Germans expelled from Eastern Europe westwards. The second largest group were Poles, millions of whom were expelled westwards from eastern Kresy region and resettled in the so-called Recovered Territories (see Allies decide Polish border in the article on the Oder-Neisse line). Hundreds of thousands of Ukrainians and some Belorussians were in the meantime expelled eastwards, from Poland to the Soviet Union. Finally, many of the several hundred thousand Jews remaining in the Eastern Europe after the Holocaust migrated outside Europe to Israel.

Migrations and climate cycles
The modern field of climate history suggests that the successive waves of Eurasian nomadic movement throughout history have had their origins in climatic cycles, which have expanded or contracted pastureland in Central Asia, especially Mongolia and the Altai. People were displaced from their home ground by other tribes trying to find land that could be grazed by essential flocks, each group pushing the next further to the south and west, into the highlands of Anatolia, the plains of Hungary, into Mesopotamia or southwards, into the rich pastures of China.

Types of migrations
*The cyclic movement which involves commuting, a seasonal movement, and nomadism.
*The periodic movement which consists of migrant labor, military services, and pastoral farming Transhumance.
*The migratory movement that moves from the eastern part of the United States to the western part. It also moves from China to southeast Asia, from Europe to North America, and from South America to the middle part of the Americas.
*Internal migration

Ravenstein's 'laws of migration'
Certain laws of social science have been proposed to describe human migration. The following was a standard list after Ravenstein's proposals during the time frame of 1834 to 1913. The laws are as follows:
Most migrants only go a short distance at one time.
Long distance migrations are for those who come from large cities.
Most migration is from rural areas to urban areas.
Most international migrants consist of young males between the ages of 20 and 45.
Most migrations proceed in step-by-step processes.
Each migration flow produces at least one counterflow.
Females remain more migratory than the males within their country.
Migration increases in volume as industries develop and transportation improves.
The economy is a major factor in migration.

Causes of migrations
Causes of migrations have modified over hundreds of years. Some cases are constant, some of them do not carry the same importance as years ago (for example: in 18th and 19th centuries labor migration did not have the same character like today).
In general we can divide factors causing migrations into two groups of factors: Push and pull factors. In general:
*Push Factors are economic, political, cultural, and environmentally based.
*Pull Factors are economic, political, cultural, and environmentally based.
*Barriers/Obstacles which is an example of Nigeria in the 1970s and 1980s.
*Some certain factors are both push and pull like education, industry etc.

Effects of migration
Migration like any other process shapes many fields of life, having both advantages and disadvantages. Effects of migrations are:
*changes in population distribution
*mixing of different cultures and races (what often leads to negative social behaviors – tensions in society between majorities and minorities, followed often by local struggles and racism and racial discrimination. Also criminality growth can be caused.
*demographic consequences: since migration is selective of particular age groups, migrants are mostly young and in productive age. It can cause a demographic crisis – population ageing, what in turn can be followed by economic problems (shrinking group of economically active population has to finance extending group of inactive population).
*economic results, which are of the greatest importance for the development of the countries.