From Asia to America: Genetics reveals new details of humanity's longest migration

One of the largest studies of populations traditionally ignored by genetics provides new details this Thursday about the longest human migration: from Asia to the southern tip of the Americas. There, in Tierra del Fuego, Chile, the Kawésqar, descendants of the humans who traveled the furthest from the original continent of all humans, Africa, still live. The new study warns that the four major native groups of South America have suffered a population decline of up to 80% in the last 10,000 years.

The new data are the result of the Genome Asia 100K Consortium, led by Nanyang Technological University in Singapore, which is focused on sequencing up to 100,000 genomes from groups underrepresented in large studies of this type. Researchers read the entire genomes of more than 1,500 people from 139 ethnic groups in Asia and the Americas. The results are published today in Science , the leading journal of global science.

Researchers have not been able to identify the Asian group from which all Native Americans descend. This is because once the first humans reached North America, American Indians migrated back to Siberia across the Bering Strait, where they interbred again with the Inuit and other natives of this region, blurring the original genetic profile. These interbreedings spanned millennia, from 5,000 years ago to just 700 years ago, the study reveals. In any case, the analysis shows that the Inuit and other present-day peoples living in the Far East of Russia remain the most closely related to all Native Americans. The separation between these two lineages occurred between 27,000 and 19,000 years ago.

The study shows that the populations of North and South America separated between 17,500 and 14,600 years ago. Shortly thereafter, between 14,000 and 10,000 years ago, the four major native lineages of South America emerged: the Andeans who occupied the highlands along the Andes; those who settled in the dry plains of the Chaco—parts of Brazil, Argentina, Bolivia, and Paraguay; the Amazonians who inhabited the jungles; and the Patagonians, who reached the southern tip of the continent. These groups suffered the consequences of geographic and genetic isolation. The topography itself contributed, as it seems that the Isthmus of Panama prevented return trips, which would have increased genetic diversity.

The four groups have experienced population declines of nearly 49% among Andeans and Chacoans, 60% among Amazonians, and 80% among Patagonians like the Kawésqar, who are "on the brink of extinction," the study warns, along with their language. The genetics of the four groups show a genetic diversity as poor as that of the Andaman natives, who have lived for centuries on remote islands in the Indian Ocean.

Despite everything, these people managed to survive for 13 millennia, even when the arrival of European conquerors decimated the populations, primarily due to imported pathogens. The current descendants of these populations continue to have less genetic diversity, including those related to immunity, which makes them more vulnerable to new infectious agents, explains Elena Gusareva , the study's first author. “Our analysis highlights the deep connection between the environment and the human genome throughout history. As people adapted to diverse and often extreme environments—such as high altitudes or cold climates—their genomes evolved accordingly. However, with rapid climate change underway, these adaptations could become incompatible with new conditions, potentially leading to future health challenges for these populations,” she reasons in an email.

Genetic variants have also been identified that promote adverse effects of some drugs, as well as beneficial adaptations, such as a better metabolism for survival in frigid climates and an adaptation to oxygen scarcity that Andean people possess, which is different from that of inhabitants of the Himalayan mountain range.

A second study published this Thursday in the same journal analyzes the genome of 2,700 Brazilians and concludes that this is one of the most genetically diverse countries on the planet, thanks to its history. After the arrival of Europeans in the 16th century, the country experienced one of the largest known human movements, with the settlement of some five million European colonists and at least five million African slaves, in a country where there were already more than 10 million natives who spoke a set of 1,000 indigenous languages. The study confirms that in past centuries, interbreeding predominated between European men, the colonists, with African or American women, probably subjugated. This pattern has changed, and current couples are much more diverse, although the genetic marks of centuries of colonization and slavery are still present.

Nearly nine million genetic variants, completely new to science, have been discovered. Some of these may have significant implications for global health, as they are linked to increased fertility, metabolism, and the immune system. In addition, more than 35,000 mutations originating in Native Africans and Americans have been detected and may be linked to various diseases.

A third study focuses on the extinction of American megafauna—giant sloths, mastodons, saber-toothed cats , etc.—around 10,000 years ago. This disaster may have affected many Native American communities that lived by hunting. Wild horses also disappeared at this time, and did not return to America until they were reintroduced by Europeans. The study analyzed nearly 70 genomes extracted from wild horse fossils dating back between 50,000 and 13,000 years. The results confirm a constant genetic exchange between animals brought from Eurasia to America and vice versa. Animal fossils found in Europe show their kinship with Americans, including specimens from the Iberian Peninsula . This healthy exchange ended when the Bering Strait Ice Bridge disappeared, and wild horses became extinct in America. The research, which aims to combine Western science with the knowledge of native communities, was led by Ivette Caballo Corredor Collin , a researcher at the University of Toulouse (France) and an Oglala Lakota Indian.