CSIS | Center for Strategic and International Studies
According to CSIS expert Mark Quarterman, director of the Program on Crisis, Conflict, and Cooperation (C3), there are many reasons why someone would migrate from his or her home to a new place. Taken together, most of these reasons can be grouped into two broad categories—pull factors and push factors.
Pull factors are conditions that attract people to a new area. Opportunity, a sense that somewhere else might offer more economic or social prospects for oneself or one’s family, is undoubtedly an aspect that pulls people to other places. Sometimes people move within a country. Examples in the United States include the settling of the West or the migration of African Americans from the south to the north. Most countries, as their economies industrialize, experience large scale migrations from rural areas to cities.
Push factors are conditions that drive people away from their homes. These negative factors include scarcity such as famine; a lack of employment opportunities; and oppression or armed conflict. Examples abound, from the large-scale Irish emigration in the mid-19th century caused by the potato famine to the economic collapse of farming in parts of the Midwest United States during the Great Depression that caused large numbers of farm families to move west. Likewise, the Holocaust forced Jewish families to flee Europe in the 1930s and 1940s. More recently, many Haitians have been prompted by a combination of economic, political, and natural factors to leave their island country on rickety ships to seek better lives in the United States.
There is no way to know exactly why humans migrated thousands of years ago. It's possible that at one point, there was too much population for an area's vegetation and other systems to support and violence erupted, causing some humans to move on. Harsh weather also contributed to migration, as flooding and drought caused problems in populated areas. War, politics and economics often caused tension among civilizations and increased competition forced people into newer areas. Cold weather may have lowered sea levels and opened up bridges that offered new paths across seas. As humans began developing more sophisticated tools, they may have been more confident or driven to explore.
One fact now is certain: Through scientific analysis of mitochondrial DNA, it's clear that every human alive today is -- very distantly -- related to one woman who lived in African 200,000 years ago [source: Smithsonian]. At some point, probably about 80,000 years ago, some of the humans began migrating. Initially, people followed the coastlines of Africa, which were abundant in resources. They began to migrate to the Middle East, southern Asia and Australia. About 40,000 years ago, humans migrated into Europe, and eventually crossed an icy bridge between Europe and North America known as "Beringia." Their path took them down the west coast of North America, although scientists debate about when this actually occurred -- more than 30,000 years ago or more recently. Finally, humans forged into South America and spread east into what is currently the United States and Canada.
This migration pattern also is supported by mitochondrial DNA evidence. A new discipline called genetic anthropology combines physical evidence with DNA to study the history of our ancient migration [source: Human Genome]. The Genographic Project is a multi-year effort to gather data on people around the world and note common DNA across geographic distances [source: Genographic]. Researchers believe this will help people better understand our genetic roots and human migration. To date, the project has begun mapping the beginning of human civilization and the migration out of Africa by era, beginning with 200,000 B.C. and ending with 10,000 B.C. The atlas shows humans reaching North America between 30,000 and 20,000 years ago.
An African migrant at the CETI, Short Stay Immigrant Center, in the Spanish Enclave of Melilla, Spain (Marco Di Lauro/Getty Images)
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