On the Peruvian side of Lake Titicaca, a peculiar sort of man-made assemblage captures the attention—the villages of the Uros people, constructed out of straw from the totora reeds that grow in those waters. The villages form floating islands with houses and moored boats called balsas—all made of straw. “The Uros use the reeds for everything, and even eat certain parts of them,” says geneticist Fabrício Santos of the Federal University of Minas Gerais (UFMG). He heads the South American Genographic Project, part of an international consortium that uses genetics to tell the story of the migration patterns used by humans since the time of their origin in Africa. In his studies of the Uros, Santos has come to an important conclusion. “From a genealogical standpoint, they have an ancestral signature that is very distinct from that of other Andean ethnic groups.” This means that the inhabitants of the floating villages—as well as the Bolivian Uros, who live on smaller lakes and do not build reed islands—are descendents of the people who were probably the first inhabitants of the Andean Plateau.
That conclusion, published in September 2013 in the journal PloS One, refutes suspicions that the people who attract tourists on the floating islands are descendents of the Aymara, dressed as Uros in order to attract visitors and profit from tourism. Doubts that these people were original Uros arose years ago, when an anthropological study revealed that the last speaker of Uruquilla, the original language of the Uros, died in the 1950s. Separated by more than 400 kilometers, the present-day communities of the Uros—those living on Lake Titicaca in Peru and on Lakes Poopó and Coipasa in Bolivia—generally speak Aymara and Spanish. “Since they are descendents of fisherman and gatherers—probably the first inhabitants of the Andean Plateau—the Uros never established large cities. They stayed in isolated groups, always living next to the water,” Santos says.
Sampling conducted by the Genographic Project in order to trace human ancestry helps unravel the origins of different ethnic groups. Before collecting the genetic material, the researchers use questionnaires to ensure that all participants are volunteers whose parents and grandparents belong to the same community and speak the traditional indigenous language. “Sometimes we find 200 people wanting to participate in the study, but they are all from the same family,” Santos says. “Since we are looking for representatives of different families, we ask that only one person from each family participate.” That strategy reduces the probability of sample bias and expands the genealogical information available from each community. The UFMG group worked in partnership with the group led by Ricardo Fujita of the Universidad San Martín de Porres in Peru, and the one headed by Susana Revollo of the Universidad Mayor de San Andrés in Bolivia. The findings were reviewed by members of the worldwide Genographic Project prior to publication.
The study analyzed DNA from 388 Uros individuals from the Andean Plateau, an arid region situated at an average altitude of 3,750 meters, between the western and eastern ranges of the Andes mountains. The sampling included populations along the Peruvian shores of Lake Titicaca, where about 2,000 people live, and near the Bolivian lakes that are home to about 2,600 Uros. The data on Y- chromosome and mitochondrial genetic variations enabled the researchers to reconstruct the paternal and maternal lineages, respectively, and revealed a great deal of heterogeneity among the different Uros groups.
SANDOVAL ET AL., PLOS ONE 2013Those findings were actually expected. The communities of Peruvian and Bolivian Uros are genetically isolated—there is no intermarriage among members of different communities—and today they are separated by a large geographic distance. Even so, the researchers were able to observe that these communities have origins that are distinct from those of other ethnic groups. “The Uros populations are generally more differentiated from the Quechuas and Aymaras than from the Arawaks, who speak Amazonian languages and live at the foot of the Andes,” Santos notes.
As for the date of colonization of the plateau, no inference could be drawn from the genetic data, but they are compatible with historical and archeological indications that the Uros arrived in the region before the other populations living there today, such as the Quechuas and the Aymaras, descendants of the Incas. “Archeologists estimate that the colonization of Lake Titicaca by non-farmers, such as the Uros of the past, took place around 3,700 years ago,” Santos says. From a genetic standpoint, the analyses show a population expansion signature only for the farming groups, who scattered their plantings of corn and potatoes around the Andes about 3,000 years ago. The fishermen stayed put in small, thinly populated groups.
The conclusions were well-received by the subject communities, to whom the researchers presented their results in May 2013 before publishing the scientific article. The first author of the article is José Sandoval, a Peruvian Aymara. To clarify the significance of the genetic findings for his hosts, Santos pointed out that, “Genetics provides just one piece of information on the ancestry of the Uros. The community can use this information as it sees fit in support of its well-documented cultural identity.” In Santos’ opinion, a community’s way of life is the most important determinant of its cultural identity, and in the case of the Uros, part of that identity has finally been recognized. In early 2013 the Peruvian government declared the customs of the Uros to be a national cultural asset, in light of their use of ancestral practices in the use of totora reeds. “Genetics can reveal significant data from a people’s unknown past,” Santos says. “With the help of science, we need to reconstruct the history of the native peoples of the Americas and present it to society.”
SANDOVAL, J.R. et al. The genetic history of indigenous populations of the Peruvian and Bolivian Altiplano: the legacy of the Uros. PloS One. V. 8, No. 9, e73006. Sept. 2013.