# The Global Impact of Human Migration

## Peopling of the World


### Learning Outcomes

By the end of this section, you will be able to:
1. Describe the early migration patterns of the genus Homo.
2. Distinguish the primary controversies in the peopling of America theories.
3. Identify major pre-Clovis sites in the United States.

### Early Hominin Migrations

Human species were migratory from the beginning, moving as small populations of gatherers and hunters within eastern and southern Africa. By following game and the availability of seasonal vegetation from place to place, these small groups of nomads learned about their landscape, interacted with each other, and met their subsistence needs. Their daily needs came through interaction with a changing environment. With the emergence of  around 1.89 million years BP (before the present), hominins expanded their territories and began to exhibit increasing control over their environment and an ability to adapt, evidenced by the development of new subsistence systems, including cultivation, pastoralism, and agriculture, and an upsurge in migration within Africa and, eventually, into Asia and Europe. This expansion into new geographical regions was a hallmark of the later human species.
There are several theories on possible migratory sequences within and beyond the African continent. One possibility is that by 1.75 million years ago, Homo ergaster had begun migrating out of Africa, moving northward into Eurasia. Another theory argues that an earlier hominin species, either australopithecine or an early as-yet-unknown species of the genus Homo, migrated out of Africa around 2 million years ago, eventually evolving into the population of Dmanisi hominins who were settled in eastern Europe by 1.85 million years ago, possibly representing another link between H. erectus and H. ergaster. Although settlement dates are currently being retested and reexamined for precision (Matsu’ura et al. 2020), it is known that between 1.3 and 1.6 million years ago, H. erectus settled on Java, an island that is now part of Indonesia. They likely traveled there by a land route, as seas were lower during the Pleistocene Ice Age (approximately 2.588 million–11,700 years ago), allowing for more passage through interior coastal routes. (For more on early human migrations, see The Genus Homo .)
Regardless of the specific time frame and migration pattern, it is well established that there was gene flow between various hominin populations, which indicates that there were migration and exchange. With the migration of these early hominin populations, cultural practices and improvements in toolmaking spread as well. Wherever humans traveled, they carried with them their traditions, intermingling and reproducing both physically and culturally.

### Controversies Surrounding the Peopling of the Americas

Current evidence points to the emergence of the genus Homo in Africa. From these beginnings, human populations began moving toward the global north, east, and south in migratory waves. Motivations for these migrations included animal movements, overcrowding and resource scarcity, and, likely, curiosity and adventure. The movement into the Western Hemisphere, into North and South America, occurred significantly later than migrations into Europe and Asia; how much later is a question of enormous controversy today. How did the first peoples make their way to the Americas? When did they first arrive, and how did they migrate within these vast continents? The available evidence is inconclusive, leaving us with one of the biggest enigmas in human evolution. While there is some debate on whether earlier human species migrated into the Americas, the evidence we have today points to members of the species  being the earliest humans to do so. At this point, there is no evidence of any earlier hominin species in either North or South America. The Western Hemisphere was wholly settled by migrants coming from other continents.
There are many theories regarding the first human migration into the Western Hemisphere. Because of changing global climate conditions and the retreat of glaciers toward the end of the Pleistocene epoch, new lands opened to migrating animals and the humans who were likely hunting them (Wooller et al. 2018). As always, because of limited and ambiguous artifact and fossil findings, the primary pieces of evidence are open to multiple interpretations. Upon examining the range of theories, two primary arguments are apparent. Both of these arguments are backed by supporting evidence, and both rely on migratory patterns of H. sapiens in the Americas that have been definitively established. While both migration theories are valid, the question that remains open to argument is which came first, coastal or interior migration?
1. The , also called the Bering Strait theory, is the best-known and most accepted theory for the first human migration into the Americas. The foundation of this theory is the Beringia “land bridge,” which connected northeast Siberia and what is now Alaska when sea levels were lower due to glacial ice formation on the continents. This theory proposes that the earliest human habitants of the Americas crossed this marshy land on foot, most likely beginning around 15,000 years ago based on artifacts and dating sequences. The Beringia land bridge was alternately exposed and submerged multiple times over the earth’s history. According to the interior route theory, the earliest humans crossed this marshy land in pursuit of migratory herds of mammals and then proceeded to filter southward, splitting into multiple groups, some of which penetrated into the interior of North America as they continued to move east and south.
      
2. The  is also based on the migration of a northeastern Siberian population into the Western Hemisphere, but by boat rather than on foot. This theory, sometimes called the kelp highway hypothesis, proposes that the earliest migratory populations followed the continental coastline southward, subsisting on kelp, fish, shellfish, birds, and sea mammals. Research by archaeologist Jon Erlandson (Erlandson et al. 2007; Ocean Wise 2017) suggests that migrants may have followed these food sources all along the continental shelf, a shallow sea area near the shore. Some believe that they eventually reached as far south as Chile, in South America, before breaking into groups and penetrating the interior lands.
Each theory presents its own probabilities and problems in relation to dating sequences and artifacts, and there were possibly multiple early routes for the peopling the Americas. Scientific research does agree on some known facts, however. Genetic sequencing shows continuity between the earliest Americans and populations in northeastern Siberia that indicates the earliest inhabitants of the Americas arrived no more than 25,000 years ago, making the Americas the most recent continental habitation (outside of Antarctica). Humans were already inhabiting Australia by the time other humans first arrived in the Americas.
Archaeological sites in the Americas present fascinating evidence of early human migrations, with the dating sequences continually being retested and revised. Based on some of the early archaeological evidence, scientists had believed that the first American inhabitants were part of what is known as the Clovis culture, identified with a leaf-shaped projectile point used in hunting. As excavations have continued, though, there is growing indication of an extensive pre-Clovis culture, evidenced by a pre-Clovis technology based on gathering, hunting, and fishing, with dates extending back further than 13,200 years before present. Pre-Clovis projectile points are smaller, less standardized, and less worked (flaked), indicating a less advanced tool production. Many pre-Clovis sites are located below the Clovis period occupation. As archaeologists have continued excavations, the dates for earliest occupation continue to be pushed backward.
Why so much debate about the settling of the Americas? There are various reasons for the difficulties in establishing settlement dates. The Bering land bridge was periodically exposed and submerged under water during periods of glacial growth and retreat. Using core samples obtained by drilling down into the shallow sea floor, archaeologists have found evidence of large mammals and even fluted points (hunting tools) in and around the Aleutian Islands, through which the land bridge would have crossed. Establishing and cross-checking dates, though, has been difficult because most evidence is now submerged. This is a challenge also for the coastal route theory, as coastlines have receded since the end of the Pleistocene, and encampments would have likely been small, possibly temporary sites. Many sites are likely now submerged offshore (Gruhn 2020).
Among the best-known pre-Clovis sites are the following:
1. , Chile. This is one of the most studied pre-Clovis sites. An extensive array of artifacts has been found at Monte Verde, including hearths, wooden and stone tools, animal bones, and even human footprints. The dates assigned to these artifacts, as early as 16,000 BP, put this site within the range of pre-Clovis dates seen in North America.
2. , Texas. This pre-Clovis site has a dating sequence of 13,500 to 15,500 BP. A wide range of pre-Clovis tools have been found here, including partially flaked tools, blades, and scrapers.
3. , Virginia. A well-document Clovis site has been identified at Cactus Hill, but below this level of artifacts, there is evidence of pre-Clovis projectile points. Although controversial, these points have possible dating sequences of 18,000–22,000 BP.
Based on this new evidence, scientists now agree that the Americas were first settled by a pre-Clovis population. How they arrived, when they arrived, what movements they made, and in what order they made them are major archaeological questions today. What we can conclude is that human populations continued to migrate after peopling the Americas.