Understanding the peopling of the Americas remains an important and challenging question. Here, we present 14C
dates, and morphological, isotopic and genomic sequence data from two
human skulls from the state of Minas Gerais, Brazil, part of one of the
indigenous groups known as ‘Botocudos’. We find that their genomic
ancestry is Polynesian, with no detectable Native American component.
Radiocarbon analysis of the skulls shows that the individuals had died
prior to the beginning of the 19th century. Our findings could either
represent genomic evidence of Polynesians reaching South America during
their Pacific expansion, or European-mediated transport.
Main Text
A
recent study of skeletal remains from Brazil belonging to the
indigenous Botocudo peoples found that two male individuals presented a
combination of mitochondrial DNA (mtDNA) variants common in present day
Oceanian populations [
].
Although it was argued that these genetic traits were likely to be
derived from runaway slaves brought to Brazil by Europeans, no
direct-dating or genomic analyses were used to support this conclusion.
The Botocudos, named after the wooden disks (‘botoques’) in their lower
lips and ear lobes, were an indigenous group with presumably Native
American origins occupying the coast and the interior of Eastern-Central
Brazil until the late 18th century, when most were
exterminated by European colonists after decades of violence. The
population size and origin of the Botocudos remain unclear, but they are
likely to have comprised several tribes who spoke a common Macro-Jê
language at the time of European contact [
].
We conducted a variety of genomic, morphological and isotopic analyses
of skeletal remains attributed to the Botocudos of Brazil.
We confined our analyses to four Botocudo individuals (Bot13, Bot15, Bot17 and Bot65; Supplemental information)
after careful review of all available records at the Museu Nacional in
Rio de Janeiro, Brazil, including an extensive archival study that
pointed to the four crania being bona fide Botocudo, a designation which is also corroborated by the labels on the skulls (Figure 1A).
Figure 1Radiocarbon and genetic evidence for Polynesian ancestry among Botocudos.
We
performed an initial DNA screening by shotgun sequencing the four
individuals, finding that only Bot15 and Bot17 yielded a endogenous
human DNA content higher than 1% (5.6% and 12.5%, respectively), thus
allowing for whole genome sequencing (Supplemental information).
In total, we obtained genetic data from the following experiments:
mtDNA capture for Bot15; single nucleotide polymorphism (SNP) capture
for 6,000 ancestry informative markers (AIMs) for Bot15; and whole
genome shotgun sequencing for Bot15 and Bot17 (to an average genomic
depth of 1.2X and 1.5X, respectively). We found features in the data
characteristic of ancient DNA (Supplemental information).
All the genetic data point towards two individuals with Polynesian
ancestry and no detectable Native American ancestry. For example, when
conducting a classical multidimensional scaling (MDS) analysis on
identity-by-state (IBS) distance-of-genotype data of worldwide
populations, including the Botocudo whole genome data, we found that the
ancient genomes fall within the Polynesian populations (Figure 1C).
Moreover, clustering analyses suggest that Bot15 and Bot17 have no
detectable Native American ancestry and share the same components as the
Polynesian population. When assuming seven ancestral populations (K
= 7), the Polynesians form their own cluster and more than 99.9% of the
genomes of Bot15 and Bot17 were assigned to this Polynesian cluster (Figure 1D).
Accelerator
mass spectrometry (AMS) radiocarbon dating of five teeth from the four
Botocudo individuals was carried out in two independent laboratories.
When calibrating the 14C dates with the Southern Hemisphere curve [
],
the 95% highest posterior density regions (HPD) were 1452–1510 AD and
1579–1620 AD for Bot15 (bimodal distribution), and 1419–1477AD for
Bot17. While there is a general lack of baseline isotope data for the
relevant areas and from archaeological remains, the combined evidence
from the δ13C, δ15N and δ34S values
when compared to Brazilian fauna and flora, as well as archaeological
and modern human bone samples, suggests that a marine reservoir effect
cannot be fully excluded (Supplemental information). The 95% HPDs of the marine corrected dates are 1479–1708 AD and 1730–1804 AD for Bot15, and 1496–1842 AD for Bot17 (Figure 1B).
More work on foodwebs and carbon cycling in the Minas Gerais area is
needed to determine if a marine reservoir correction for the 14C
dates is indeed required; hence, the marine-corrected age estimates
presented must be considered highly conservative. Strontium analysis and
craniometry results are detailed in the Supplemental information.
Several
scenarios have been previously proposed that are of potential relevance
for explaining our result that two Botocudo individuals have Polynesian
ancestry for both the mitochondrial and nuclear genomes [
],
the Madagascar–Brazil slave trade, voyaging on European ships either as
crew, passengers, or stowaways, and Polynesian voyaging. Regardless,
the scenario must necessarily invoke a certain number of Polynesian
migrants — presumably more than two, as we detected Polynesian ancestry
in two out of 35 Botocudo individuals in the Museu Nacional collection. A
detailed investigation of these possibilities can be found in the Supplemental information. The 1862–1864 AD Peru–Polynesia slave trade can be excluded, given that the 14C
calibrated dates for the skulls predate the beginning of this trade.
The Madagascar–Brazil slave trade is of relevance, as Madagascar is
known to have been peopled by Southeast Asians [
].
However, we can further exclude this hypothesis as recent genomic data
have demonstrated that the Malagasy ancestors admixed with African
populations prior to the slave trade [
], and no such ancestry is detected in our Botocudo sample (Supplemental information). Furthermore, Madagascar was peopled by Southeast Asian and not Polynesian populations.
While
Fernão de Magalhães (Magellan) first spotted some seemingly uninhabited
Polynesian islands in 1521 AD, the lack of precise navigational
techniques [
],
as well as war between European nations, meant that many of those
islands were not visited by Europeans again for at least another 200
years. Therefore, trade involving Euroamerican ships in the Pacific only
began after 1760 AD [
]. By 1760 AD, Bot15 and Bot17 were already deceased with a probability of 0.92 and 0.81, respectively (Supplemental information),
making this scenario unlikely. Although improbable also because it
would involve both individuals making it to the interior of Brazil, we
cannot exclude this scenario.
Polynesian
ancestors originated from East Asia and on their migration eastwards
interacted with and admixed with local New Guineans before colonizing
the Pacific. In recent years, evidence has continued to accumulate in
favor of a Polynesian and South American contact [
]).
It has been established that the Polynesian Pacific expansion from
Southeast Asia covered distances of thousands of kilometers, reaching
New Zealand, Hawaii and Easter Island — an area approximately the size
of North America — between ca. 1200 and 1300 AD [
].
It is hard to explain how the first possible genomic evidence of such
Polynesian contact with South America would be found in Brazil rather
than on the west coast of South America, yet we cannot exclude this
scenario either.
Whether brought by
Europeans or the result of the Polynesian expansion, the fact remains
that some Brazilian Botocudos carried distinctive Polynesian genetic
signatures. We hope that further sampling will provide a more definitive
answer to this intriguing finding.
Acknowledgments
We
would like to thank the laboratory technicians at the Danish National
High-throughput DNA Sequencing Centre for technical assistance; Martin
Kircher, Thorfinn Sand Korneliussen, Johannes Krause, David Reich, Erik
Thorsby for helpful discussion; Toomas Kivisild, Jinchuan Xing, Andreas
Wollstein, David Reich for early access and/or assistance with their
data. GeoGenetics members were supported by the Lundbeck Foundation, the
Danish National Research Foundation (DNRF94) and the European Union
(FP7/2007-2013/317184 and 319209). A.S.M. was supported by a fellowship
from the Swiss National Science Foundation (PBSKP3_143529); M.D. by the
US National Science Foundation (grant DBI-1103639); P.L.J. by the
National Institutes of Health (grant K99 GM104158); V.F.G. by a
Strategic Training for Advanced Genetic Epidemiology (STAGE) fellowship,
University of Toronto.
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