Human Migration

Migration Patterns of Early Ancestors

Once Common Ancestor from Africa

Human migration is the movement by people from one place to another with the intentions of settling temporarily or permanently in the new location. The movement is typically over long distances and from one country to another, but internal migration is also possible. Migration may be individuals, family units or in large groups.

Nomadic movements are normally not regarded as migrations as there is no intention to settle in the new place and because the movement is generally seasonal. Only a few nomadic peoples have retained this form of lifestyle in modern times. Also, the temporary movement of people for the purpose of travel, tourism, pilgrimages, or the commute is not regarded as migration, in the absence of an intention to live and settle in other places.

When humans first ventured out of Africa, they left genetic footprints still visible today. By mapping the appearance and frequency of genetic markers in modern peoples, we create a picture of when and where ancient humans moved around the world. These great migrations eventually led the descendants of a small group of Africans to occupy even the farthest reaches of the Earth.

Our species is an African one: Africa is where we first evolved, and where we have spent the majority of our time on Earth. The earliest fossils of recognizably modern Homo sapiens appear in the fossil record at Omo Kibish in Ethiopia. Although earlier fossils may be found over the coming years, this is our best understanding of when and approximately where we originated.

According to the genetic and paleontological record, we only started to leave Africa between 60,000 and 70,000 years ago. What set this in motion is uncertain, but we think it has something to do with major climatic shifts that were happening around that time—a sudden cooling in the Earth’s climate driven by the onset of one of the worst parts of the last Ice Age. This cold snap would have made life difficult for our African ancestors, and the genetic evidence points to a sharp reduction in population size around this time. In fact, the human population likely dropped to fewer than 10,000. We were holding on by a thread.

Once the climate started to improve, we came back from this near-extinction event. The population expanded, and some intrepid explorers ventured beyond Africa. The earliest people to colonize the Eurasian landmass likely did so across the Bab-al-Mandab Strait separating present-day Yemen from Djibouti. These early beachcombers expanded rapidly along the coast to India, and reached Southeast Asia and Australia. The first great foray of our species beyond Africa had led us all the way across the globe.

Slightly later, a second group appears to have set out on an inland trek, leaving behind the certainties of life in the tropics to head out into the Middle East and southern Central Asia. From these base camps, they were poised to colonize the northern latitudes of Asia, Europe, and beyond.

A small group of these Asian hunters headed into the face of the storm, entering the East Asian Arctic during the Last Glacial Maximum. At this time the great ice sheets covering the far north had literally sucked up much of the Earth’s moisture in their vast expanses of white wasteland, dropping sea levels by more than 300 feet. This exposed a land bridge that connected the Old World to the New, joining Asia to the Americas. In crossing it, the hunters had made the final great leap of the human journey. They had penetrated the land south of the ice, and within 1,000 years they had made it all the way to the tip of South America. Some may have even made the journey by sea.

The story doesn’t end there, of course. The rise of agriculture and the population explosion it created—has left a dramatic impact on the human gene pool. The rise of empires, the astounding oceangoing voyages of the Polynesians, even the extraordinary increase in global migration over the past 500 years could all leave traces in our DNA. There are many human journey questions waiting to be asked and answered.

Types of Migration

Internal Migration: Moving to a new home within a state, country, or continent.

External Migration: Moving to a new home in a different state, country, or continent.

Emigration: Leaving one country to move to another (e.g., the Pilgrims emigrated from England).

Immigration: Moving into a new country (e.g., the Pilgrims immigrated to America).

Population Transfer: When a government forces a large group of people out of a region, usually based on ethnicity or religion. This is also known as an involuntary or forced migration.

Impelled Migration (also called "reluctant" or "imposed" migration): Individuals are not forced out of their country, but leave because of unfavorable situations such as warfare, political problems, or religious persecution.

Step Migration: A series of shorter, less extreme migrations from a person's place of origin to final destination—such as moving from a farm, to a village, to a town, and finally to a city.

Chain Migration: A series of migrations within a family or defined group of people. A chain migration often begins with one family member who sends money to bring other family members to the new location. Chain migration results in migration fields—the clustering of people from a specific region into certain neighborhoods or small towns.

Return Migration: The voluntary movements of immigrants back to their place of origin. This is also known as circular migration.

Seasonal Migration: The process of moving for a period of time in response to labor or climate conditions (e.g., farm workers following crop harvests or working in cities off-season; "snowbirds" moving to the southern and southwestern United States during winter).

Early Human Migration

No historical record exists that tracks the migratory patterns of the earliest humans. Scientists piece together the story of human migration by examining the tools, art and burial sites they left behind and by tracing genetic patterns. They accomplish this by looking atmitochondrial DNA (mtDNA), which is passed from a mother to her offspring without being blended with the genetic code of the father. We can look at the mtDNA of two people who lived thousands of miles and years apart, and if their mtDNA genetic code is the same, we know they were ancestor and descendant [source: PBS NOVA].

Examining mtDNA is useful for another reason -- it accumulates mutations relatively quickly. Scientists can see how many mutations are present and roughly determine how old that genetic line is. By comparing the number of mtDNA mutations found in people from different locations, we can tell where humans arrived first. The more mutations, the longer humans have lived in that area. All of the mtDNA found in certain parts of Africa has more mutations than any other mtDNA in the world. This evidence strongly supports the Out of Africa theory. However, even with these clues, much about early human migration is uncertain.

Early Migration Routes

When humans first left Africa, they followed the coasts, where resources were abundant. The first wave moved across the Middle East, into southern Asia, and eventually all the way down to Australia [source:National Geographic]. This occurred roughly between 90,000 and 30,000 years ago [source: Haywood]. Additional waves of migration followed. Between 40,000 and 12,000 years ago, humans moved north into Europe. However, their range was limited by an ice sheet that extended into the northern part of continental Europe.

The icy conditions at the time also helped expand early humanity's territory. A massive sheet of ice, combined with lower sea levels, formed a bridge between Siberia and Alaska that we call Beringia. The first humans crossed over 30,000 years ago, moving down the west coast of North America [source:National Geographic]. Other sources suggest a more recent North American migration, starting about 15,000 years ago [source: Haywood]. New evidence seems to keep pushing the date of first North American habitation further and further back. Humans eventually spread into South America and pushed east into what is now the eastern United States and Canada. This theory of North America's settlement is supported by mtDNA evidence and a similarity in the dental structures of Siberian and North American populations of the era.

There have long been competing theories that early humans crossed the Atlantic Ocean, either from Africa to South America or the Caribbean, or from Europe to Greenland to North America. While it may have been possible to make such a trip using available seafaring technology, it is unlikely that a large-scale migration occurred in such a way.

The initial spread of humanity across the Earth was driven primarily by food and climate. Nomadic tribes of up to a few dozen people likely followed the migration patterns of the herd animals they hunted. Climate change opened new areas for hunting, even as technology such as mastery of fire and meat preserving allowed humans to live in less-than-ideal conditions. The human ability to adapt to new circumstances not only gave early humans an advantage over Homo erectus, it also facilitated global expansion.

CONTINENTAL DRIFT?

The movement of tectonic plates means that land masses that are now thousands of miles apart were once linked as one huge supercontinent, called Pangea. This had a huge influence on animal migrations, as scientists have found fossil remains of identical creatures in distant, unconnected places. Some Scientist however feel that Human migration was not affected. Why? They consider that humanity is too new. They suggest that according to evolution by the time the first humans appeared, the continents were already pretty much in their present-day positions. However, if the theory that humans are far older than believed by some scientist this could be a valuable theory indeed.

Expanding Earth theory (Growing Earth theory)

Another theory for human migration to the new continent involves a new theoriey called the Expanding Earth theory (Growing Earth theory) and an Exchanging Earth with the rest of the solar system and universe?

The Expanding Earth theory is an interesting idea especially with the stunning visual ‘evidence’ – The Earths continents also appear to fit perfectly together on a smaller planet, to form a ‘supercontinent’ that would be the Earths surface.

The Growing Earth or Expanding Earth theory suggests that instead of the supercontinents theory, the planet has expanded from its original supercontinent that was the whole Earths surface. Over the centuries there have been a lot of theories about a hollow earth and an expanding Earth and how or what processes could cause a planet to grow. The video above is by Neal Adams who reignited the expanding Earth debate.

Neil Adams has his own unique ideas about the mechanics of how the planet could have grown. They are not necessarily what others who are interested in exploring the idea of the possibility of the planets having expanded at some time in the past. It is worth mentioning at this point that an event like this could be a good explanation for a sudden flood on earth. If the Earth's core held pressurized water which was contined by its surface land then a sudden break in its core at the platetechtonics releasing the waters and causing the land mass to move as Earth expands would certainly fit into the Genesis account of a "Great Flood". It would certainly have been something that God would have known and for the creatures in that area been devastating. We will later present more evidence that support the theory of a "Great Flood", but we though it would be worth mentioning it at this point as well for your consideration.

EXCHANGING EARTH

But how or what would trigger, cause, energise an Expanding Earth? What processes or mechanism could help with a Growing Earth? Could the energy and perhaps if extra mass is needed, come from what seems to be planet Earth receiving and exchanging energy and molecules/matter with our Sun and perhaps in a circuit with our solar system? With the other solar system bodies such as planets, moons, active asteroids and comets part of a plasma circuit and solar system engine?

There are certainly plenty of theories to fill the imagination. As a learniner and would be Scientist your job is to explore all the theories, examines all the evidence and draw your own conclusions. While no one can guarentee that there isn't some form of bias (prejudice in favor of or against one thing, person, or group compared with another, usually in a way considered to be unfair.) in the theories presented it is the indiviauls responsiblity to always seek for truth. Remember we suggest that you always examine everything, test everything, and never stop asking the questions.

THE COASTAL ROUTE

The migration from Siberia to North America might not have been made over an ice/land bridge called the Bering Straight. Another theory suggests the settlers used a sea route that hugged the coasts and islands along the way.

They stopped at the small pockets of land that weren't covered in ice, eventually getting far enough south that the land was free of ice altogether [source: National Geographic]. Migrating from out of Africa and over the continent of Asia these settlers eventually made their way into the new land unknowing that they had discovered an unknown continent.

Why People Migrate

What drove those first humans to leave Africa? That's best explained by examining the forces that continue to drive humans to migrate even today.

A population of humans living in a given area faces certain pressures. Those pressures depend on the size of the population, the resources available and the community's ability to exploit those resources.

Food - The most basic population pressure, and the one that likely drove the earliest migrations out of Africa, is food. An area of land can only support a certain population with the food produced there. Modern agricultural techniques and technologies can vastly increase food output, but in the African forests and savannas of 100,000 years ago, humans subsisted by hunting and gathering. If the population grew too large, there wouldn't be enough meat or fruit to feed everyone. A portion of the population could simply move a few miles away to find new hunting grounds. Humans may only have moved a few dozen miles per generation, but over tens of thousands of years, this slow but inexorable migration spread humans throughout Europeand Asia.

Space - You can only pack so many humans into a given space. Improvements in medical and sanitation technology make the exact limit enormously variable, and often far higher than the food limit mentioned above, but at some point the population becomes too large for the area. This can lead to outbreaks of violence or the spread of virulent diseases. A general decline in living conditions leads some people to move elsewhere.

Weather and climate - In the short term, weather events can drive a population out of one area. Flooding and severe storms can cause this. Long-term migration patterns have been shaped by climate change. A drought that turns a once-fertile area into a desert will drive the population to find a new home. Changes in sea level can reveal large stretches of coastal land. Massive sections of frozen ocean that occurred during the most recent ice age gave humans access to parts of the world they might not otherwise have reached [source:INSTAAR].

Other Reasons to Migrate

War and politics - One could argue that almost every conflict in human history can be traced to population pressure, which means that war and political oppression might just be symptoms ofpopulation pressure. It was oppression that drove English Puritans to settle in North America after first fleeing England for Holland. Today, an estimated two million refugees have fled their home country of Iraq as a result of the war, dispersing themselves throughout the Middle East; another two million have been displaced from their homes within Iraq [source: Human Rights Watch].

Economics - In terms of population pressure, money is a stand-in for food. Ever since the Industrial Revolution, few people grow and harvest the food they eat. We purchase it instead. Now, instead of moving to where the food is, people move to where the money is. These migrations can be slow shifts, such as the decline of population in the northeastern U.S. as the steel industry declined. They can also happen quickly. A major new factory built in a town can draw thousands of workers, plus thousands more who will earn money selling food, clothing and entertainment to the workers.

This illustrates the fact that economic migrations don't follow the same patterns as food migrations. Where food is concerned, higher populations make it harder for everyone to get enough food. Conversely, economies thrive on saturated population levels. More people equals more money.

The human spirit -This form of population pressure can't really be measured, but it shouldn't be taken lightly. Humans have an innate desire to explore and colonize new territories. Even when not driven by hunger, politics or economics, humans migrate.

Technology and Migration

The Agricultural Revolution

Every human group survived as hunter-gatherers for thousands of years. About 10,000 years ago, humans first developed farming technology. This technology didn't develop at one location and then slowly spread throughout the world -- it appeared independently in many different places. Agriculture was successful because it could support greater populations with less land.

The end of the Ice Age improved climate conditions in many regions, making farming more lucrative. While many societies maintained a hunter-gatherer existence even into modern times, the success of agriculture effectively ended the widespread constant human migrations that were part of the nomadic hunter lifestyle worldwide. Humans still migrated after the development of farming, but it was no longer the central aspect of their lives.

The migration that did occur was still driven by the same basic reasons -- climate and food. Instead of migrating to follow animal herds, people would migrate to areas of better soil. Without modern farming techniques, early farmers could use up all the nutrients in the soil within a generation or two, forcing migration to unfarmed land. Climate shifts could cause droughts or floods that forced migrations as well.

Migrations tend to follow paths where resources are easy to come by. Coasts and rivers, which provide fish and fertile land, are almost always settled first. Humans didn't push inland or into less hospitable areas until population pressures forced them to.

Agriculture had an enormous effect on humanity. It formed the basis for all modern human civilization. The end of constant migration and the ability to support larger populations lead to the creation of cities, states, governments, organized religions, monetary systems and militaries. None of these would be possible with a nomadic population.

The Industrial Revolution

The thousands of years which followed the development of agriculture were certainly not migration-free, but the next event that wrought massive changes on the nature of migration was the Industrial Revolution. During the 17th and 18th centuries, the Industrial Revolution mechanized the production of goods and food. It also lead to the ongoing urbanization of the world. Prior to the Industrial Revolution, communities remained relatively small, with decentralized economic centers that served each town. For example, a town might have a mill that processed grain from a few nearby farms and a few small manufacturing facilities run by local craftsmen. Industrialization saw the dawn of factories, massive manufacturing centers that offered hundreds or thousands of jobs. People migrated from rural or semi-rural areas to cities to take advantage of these plentiful jobs.

Expansion Out of the Old World

Homo sapiens began migrating into the lower latitudes of East Asia. Along the way, some of them interbred with archaic humans, including both Neandertals and Denisovans. Genetic markers from these archaic human populations are found in the gene pool of some Southern Chinese, New Guinean, and other Micronesian Island populations today. Homo sapiens from Southeast Asia travelled to Australia, because it was not connected to Southeast Asia by land. It is probable that these first Australian Aborigines arrived by simple boats or rafts.

Modern humans reached the Japanese Islands somewhat earlier and then Homo sapiens big game hunters moved into Northeastern Siberia. Some of them migrated into North America via the Bering Plain, or Beringia. Some Homo sapiens may have reached the Americas a bit earlier than this, but the evidence is still considered questionable by most paleoanthropologists. The Bering Plain intercontinental land connection is theorized to have appeared between Siberia and Alaska as a result of sea levels dropping up to 450 feet (137 m.) during the final major cold period of the last ice age.

A consequence of human migrations into new regions of the world has been the extinction of many animal species indigenous to those areas. Human hunters in the New World apparently had played a part in the extermination of 135 species of mammals, including 3/4 of the larger ones (mammoths, mastodons, giant sloths, etc.). Most of these extinctions apparently occurred within a few hundred years. It is likely that the rapidly changing climate at the end of the last ice age was a contributing factor. However, the addition of human hunters with spears to the existing top predators (mostly saber-toothed cats, lions, and dire-wolves) very likely disrupted the equilibrium between large herbivores and their predators. As a consequence there was a major ecosystem disruption resulting in the rapid decline of both non-human carnivores and their prey. Humans were very likely the trigger that set off this "trophic cascade". Unlike most other major predators, people survived by switching their food quest to smaller animals and plants.

Following the arrival of aboriginal people in Australia and Polynesians in New Zealand there were similar dramatic animal extinctions. In both of these cases humans apparentlywere directly responsible for wiping out easily hunted species. Large vulnerable marsupials were the main victims in Australia. Shortly following the arrival of humans, approximately 90% of the marsupial species larger than a domesticated cat had become extinct there. In New Zealand, it was mostly large flightless birds that were driven to extinction by human hunters following their arrival in the 10th-13th centuries A.D.

It is sobering to realize that the rate of animal and plant extinction has once again accelerated dramatically. During the last century and a half, the explosion in our global human population and our rapid technological development has allowed us to move into and over-exploit most areas of our planet including the oceans. That exploitation has usually involved cutting down forests, changing the courses of rivers, pushing wild animals and plants out of farm and urban areas, polluting wetlands with pesticides and other man-made chemicals, and industrial-scale hunting of large land animals, whales, and fish. During the early 19th century, there were at least 40,000,000 bison roaming the Great Plains of North America. By the end of that century, there were only a few hundred remaining. They had been hunted to near extinction with guns. The same fate came to the African elephant and rhinoceros during the 20th century. Likewise, commercial fishermen have depleted one species of fish after another during the last half century. Governments have had to step in to try to stem the tide of these human population effects on other species. However, they have been only marginally successful. The World Conservation Union conservatively estimates that 7,266 animal species and 8,323 plant and lichen species are now at risk of extinction primarily due to human caused habitat degradation. The endangered list includes 1/3 of all amphibian species, nearly 1/2 of the turtles and tortoises, 1/4 of the mammals, 1/5 of the sharks and rays, and 1/8 of the birds. This list does not include the many millions of species that are still unknown to science. It is likely that most of them will become extinct before they can be described and studied.

People Today

Are we genetically different from our Homo sapiens ancestors who lived years ago? The answer is almost certainly yes. In fact, it is very likely that the rate of evolution for our species has continuously accelerated since the end of the last ice age. This is mostly due to the fact that our human population has explosively grown and moved into new kinds of environments, including cities, where we have been subject to new natural selection pressures. For instance, our larger and denser populations have made it far easier for contagious diseases, such as tuberculosis, small pox, the plague, and influenza to rapidly spread through communities and wreak havoc. This has exerted strong selection for individuals who were fortunate to have immune systems that allowed them to survive. There also has been a marked change in diet for most people since the end of the last ice age. It is now less varied and predominantly vegetarian around the globe with a heavy dependence on foods made from cereal grains. It is likely that the human species has been able to adapt to these and other new environmental pressures because it has acquired a steadily greater genetic diversity. A larger population naturally has more mutations adding variation to its gene pool simply because there are more people. This happens even if the mutation rate per person remains the same. However, the mutation rate may have actually increased because we have been exposed to new kinds of man-made environmental pollution that can cause additional mutations.

It is likely that the human species has been able to adapt to these and other new environmental pressures because it has acquired a steadily greater genetic diversity. A larger population naturally has more mutations adding variation to its gene pool simply because there are more people. This happens even if the mutation rate per person remains the same. However, the mutation rate may have actually increased because we have been exposed to new kinds of man-made environmental pollution that can cause additional mutations.

It is not clear what all of the consequences of the environmental and behavioral changes for humans have been. However, it does appear that the average human body size has become somewhat shorter over the last 10,000 years, and we have acquired widespread immunity to the more severe effects of some diseases such as measles and influenza.