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Peopling time, spatial occupation and demography of Late
PleistoceneeHolocene human population from Patagonia
S. Ivan Perez
a
,
b
,
*
, María B
arbara Postillone
b
,
c
, Diego Rindel
b
,
d
, Diego Gobbo
b
,
e
,
Paula N. Gonzalez
a
,
b
, Valeria Bernal
a
,
b
a
Divisi
on Antropología, Facultad de Ciencias Naturales y Museo (UNLP), 122 and 60, La Plata, Argentina
b
Consejo Nacional de Investigaciones Científicas y T
ecnicas (CONICET), Argentina
c
Departamento de Ciencias Naturales y Antropol
ogicas, Centro de Estudios Biom
edicos, Biotecnol
ogicos, Ambientales y de Diagn
ostico (CEBBAD),
Universidad Maim
onides, Hidalgo 775, Ciudad Aut
onoma de Buenos Aires, Argentina
d
Instituto Nacional de Antropología y Pensamiento Latinoamericano (INAPL), 3 de Febrero 1378, Ciudad Aut
onoma de Buenos Aires, Argentina
e
Divisi
on Arqueología, Facultad de Ciencias Naturales y Museo (UNLP). Paseo del Bosque S/N, La Plata, Argentina
article info
Article history:
Available online 10 June 2016
Keywords:
Radiocarbon dates
Molecular data
Spatial and temporal statistics
Bayesian estimation
Hunter-gatherers
abstract
The settlement of Patagonia has been the subject of extensive research, although key questions about the
timing of arrival of the first humans and the subsequent patterns of dispersal and demographic changes
within the region remain largely unresolved. In this study we evaluated the most probable date for the
initial peopling of Patagonia and explored the temporal and spatial changes in population size along Late
PleistoceneeHolocene by using robust statistical methods for the analysis of radiocarbon dates and
molecular data. We suggest that the first humans probably arrived to Patagonia around 17,000
e14,000 years BP, a few thousands of years earlier than generally stated. Within the region, the pop-
ulations experienced a sustained and slow growth until the transition PleistoceneeHolocene, when the
population size started to increase, with a remarkable acceleration after 7000e5000 years BP and
reaching its maximum at 1000 years BP. The spatial occupation was not homogeneous across the region
though, changing from a more intense continental occupation to a coastal occupation in the Late Ho-
locene. This pattern of peopling and population expansion, obtained here on the basis of a rigorous and
comprehensive quantitative approach, will allow the future evaluation of formal models about the
ecological and cultural processes that drove the evolution of the human populations from Patagonia.
©2016 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction
Patagonia was the last continental region of the world to be
colonized by modern humans. The archaeological evidence most
widely accepted suggests that they spread into the region from the
Northwest of South America by around 14,000 years ago, probably
following the Pacific coast and reaching southern Patagonia ca.
13,000 years ago (Miotti and Salemme, 2003; Steele and Politis,
2009; Prates et al., 2013). There is increasing genetic data, from
modern and ancient mtDNA and Y chromosome, supporting that
the early populations that inhabited the region descended from
Asian groups. This evidence also points out that early populations
probably gave rise to Late Holocene and historic populations, sug-
gesting a local biological evolution of Patagonian groups (Moraga
et al., 2000; Garcıa-Bour et al., 2004; Goebel et al., 2008; Perego
et al., 2010; Bodner et al., 2012; de Saint Pierre et al., 2012a). The
spatial pattern of early human occupations in Patagonia seemed to
have occurred almost simultaneously along the Atlantic and Pacific
coasts, while the Andean foothills were colonized much later
(Borrero, 1994e1995; Miotti and Salemme, 2003; Prates et al.,
2013). Previous studies also postulate that human populations
were small and stable along Late Pleistocene and Early Holocene,
and that an increase in the occupation density only occurred during
the Late Holocene, particularly during the last 1000 to 500 years BP
(Martínez et al., 2013; Barberena et al., 2015; Zubimendi et al.,
2015). It has also been postulated that in some areas of Patagonia
population density decreased during the Middle Holocene
*Corresponding author. Divisi
on Antropología, Facultad de Ciencias Naturales y
Museo (UNLP), 122 and 60, La Plata, Argentina.
E-mail addresses: ivanperezmorea@gmail.com (S.I. Perez), mbpostillone@gmail.
com (M.B. Postillone), drindelarqueo@yahoo.com (D. Rindel), dgobbo@fcnym.unlp.
edu.ar (D. Gobbo), paulan.gonza@gmail.com (P.N. Gonzalez), bernal.valeria@gmail.
com (V. Bernal).
Contents lists available at ScienceDirect
Quaternary International
journal homepage: www.elsevier.com/locate/quaint
http://dx.doi.org/10.1016/j.quaint.2016.05.004
1040-6182/©2016 Elsevier Ltd and INQUA. All rights reserved.
Quaternary International 425 (2016) 214e223
(Barrientos and Perez, 2005; Neme and Gil, 2008; Salemme and
Miotti, 2008). In spite of these apparent agreements, the timing
and process of peopling as well as demographic changes in Pata-
gonia have been the focus of intense debate for the last decades
(Kelly, 2003; Goebel et al., 2008; Salemme and Miotti, 2008;
Dillehay, 2009; Steele and Politis, 2009; M
endez et al., 2015).
In order to address these issues, significant effort has been
devoted to obtain extensive databases of radiocarbon dates, while
the conceptual and methodological approaches to analyze them
have received less attention. In this sense, the pattern of dates is
usually taken as a direct evidence of the initial peopling and de-
mographic dynamic of the Patagonian populations. However, these
assumptions are at least arguable. First, it has long been accepted
that the archaeological record is incomplete and longtime gaps may
exist between the oldest known archaeological evidence and the
initial peopling (Marshall, 1990; Saltr
e et al., 2015; Villavicencio
et al., 2015). Therefore, the earliest dated site cannot be assumed
as the evidence of the first peopling in a given region. Additionally,
it is widely recognized that the taphonomic processes, sample size
and sampling strategies of radiocarbon dates can generate biases in
the estimations of the spatial occupation and demographic dy-
namics of hunter-gatherer groups (Williams, 2012; Timpson et al.,
2015; Torfing, 2015). Given that these conceptual and methodo-
logical problems have not been taken into account in previous
studies, the temporal and spatial processes of Patagonian peopling
are far from being well described and understood.
In this study, we estimate the most probable time for the earliest
peopling of Patagonia and explore the temporal changes in popula-
tion size along Late PleistoceneeHolocene by using robust statistical
methods for the analysisof radiocarbon dates. Wealso investigate the
temporal changesin the spatial occupation and population densityof
the region. In addition, we obtained independent estimations of the
earliest peopling and posterior demographic changes using molec-
ular data. Here we study the peopling time, spatial occupation (or
geographic distribution) and demography together because they are
part of the same process of colonization and posterior population
dynamic in a region (Drummond et al., 2005; Avise, 2009; Lemey
et al., 2009). To investigate the time and temporal dynamic of
peopling we assembled a comprehensive dataset of radiocarbon
dates of archaeological sites from thesouthern cone of South America
and analyzed them by means of time series and stratigraphic statis-
tics (Marshall, 1990; Surovell and Brantingham, 2007; Williams,
2012; Shennan et al., 2013; Saltr
eetal.,2015). The spatial occupa-
tion of the region was explored using the distribution of the fre-
quency of radiocarbon dates employing spatial statistical analyses
(Legendre and Legendre, 1998). The molecular-based estimations of
the earliest time of Patagonian peopling and the posterior de-
mographic changes were performed using modern and ancient
mtDNA data and Bayesian methods (Drummond et al., 2005; Ho and
Shapiro, 2011; Perez et al., 2016).
2. Material and methods
2.1. Radiocarbon and molecular data
We assembled a dataset of 1785 radiocarbon dates from
different bioarchaeological and archaeological sites from South
Buenos Aires and Mendoza to Tierra del Fuego (between 36 and 55
degree of South Latitude; Fig. 1;Table A.1;Borrero and Franco,
2000; Gil, 2006; Salemme and Miotti, 2008; Tessone and Belardi,
2010; Boschín and Andrade, 2011; Morello et al., 2012; Fern
andez
et al., 2013; Martínez et al., 2013; Prates et al., 2013; San Rom
an,
2013; Gil et al., 2014; Pallo and Ozan, 2014; Barberena et al.,
2015; Ber
on, 2015; Campbell and Quiroz, 2015; García Guraieb
et al., 2015; Martínez et al., 2015; Zubimendi et al., 2015; Perez
et al., 2016). Sites from neighbor areas such as Southern Cuyo and
South Pampa were also included because they have been previously
discussed together with Patagonian sites in studies that address the
peopling of this region. The final dataset was generated after
eliminating dates of the same site that overlapped in the informed
standard deviation, including in the dataset the dates with the
narrower standard deviation. In this way, we avoid possible biases
related to the intensity of excavation in the same archaeological site
or the quantity of economic resources invested for investigating
specific periods of greatest interest (e.g. the early peopling of the
region). All dates were calibrated using the Calib 7.0 software and
the SHCal13 Southern Hemisphere Calibration Curve (Stuiver et al.,
2014).
Modern and ancient human mitochondrial DNA (mtDNA) se-
quences were downloaded of the GenBank database and of previ-
ous publications (Table A.2;Ginther et al., 1993; Moraga et al.,
2000; Garcıa-Bour et al., 2004; Perego et al., 2009; Bobillo et al.,
2010; Moraga et al., 2010; Catelli et al., 2011; Bodner et al., 2012;
de Saint Pierre et al., 2012a, 2012b; de la Fuente et al., 2015). We
analyzed sequences from descendants of aboriginal populations
carrying mtDNA variants (haplotypes) with high frequencies and/or
mainly restricted to populations from the extreme south of South
Fig. 1. Distribution of studied archaeological sites (red points), current coastline (black
line) and the estimated coastlines at 11,500 Cal BP (green line) and 17,000 Cal BP (blue
line). The coastlines are drawn following Prates and collaborators (2013). (For inter-
pretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
S.I. Perez et al. / Quaternary International 425 (2016) 214e223 215
America. The 295 studied sequences comprise 1016 base pair (bp)
corresponding to the mtDNA control region (rCRS positions
approximately between 16,024 and 576) and were aligned with
MAFFT v7.012b, using the default setting (Katoh and Standley,
2013). Sequences from cosmopolitan populations and haplotypes
with high frequency outside Patagonia were not included in the
analyses.
2.2. Radiocarbon based analyses
2.2.1. Time of the earliest peopling
If the initial peopling of Patagonia was by very small and highly
mobile groups of hunter-gatherers, it is likely that their archaeo-
logical record would be sparse and the chances of being discovered
very low (Borrero, 1989e1990, 2009). With an incomplete archae-
ological record, the oldest radiocarbon date in a region is typically
posterior to the actual time of the first arrival of human groups into
the region. In that case, the estimation of the timing of initial
peopling should incorporate the uncertainties imposed by the
characteristics of the formation process of the archaeological re-
cord. This can be achieved by adding confidence intervals to the end
of the range of strata with evidence of occupation. Here, we applied
the frequentist method of Confidence Intervals on Stratigraphic
Range implemented in PAST 3.09 (Hammer et al., 2001; Hammer
and Harper, 2006), based in the methods proposed by Strauss and
Sadler (1989) and Marshall (1990). To estimate the confidence in-
tervals for the temporal depth of the archaeological record in a
given area this method takes into account the dates of the first and
last occupied strata, and the total number of strata with evidence of
occupation. The method assumes that the deposition of archaeo-
logical remains follows a random (Poisson) distribution, where the
earliest events have a lower probability of deposition (Hammer and
Harper, 2006). The earliest evidence of occupation was established
alternatively in 13,000 and 14,000 years, using the most robust and
conservative evidence of radiocarbon dates for the southern cone of
South America (Steele and Politis, 2009). The estimation of the
stratigraphic sequence of Patagonia was based on caves with well-
established sequences and reliable radiocarbon dates (e.g. Piedra
Museo, Fell, CCP7 caves; Emperaire et al., 1963; Miotti, 1996; de
Nigris, 2004; Marchionni, 2013). These sites have between 10 and
20 strata; therefore, the estimations were made using a range of
strata values to assess the effect of the number of strata used on the
estimations of the confidence intervals.
The methods of Strauss and Sadler (1989) and Marshall (1990)
have been criticized because they do not incorporate the un-
certainties associated with the radiometric dates and assume that
the likelihood of finding evidence of occupation is the same along
the true range. However, it is well known that this probability in-
creases as the region is occupied and varies in relation to changing
taphonomic conditions (Villavicencio et al., 2015). To formally
incorporate these factors in our estimations, we also infer the time
of the initial peopling of Patagonia employing one method imple-
mented by Saltr
e and collaborators (2015) provides a 95% confi-
dence band around the estimated time of peopling. This method,
called Gaussian-resampled inverse-weighted method (GRIWM),
deals with non-random deposition of archaeological remains by
progressively up-weighting the gap sizes the closer they are to the
time of the initial peopling (Bradshaw et al., 2012). This estimation
was then compared to the results obtained with the methods of
Strauss and Sadler (1989) and Marshall (1997) implemented by
Saltr
e et al. (2015). These estimations were obtained in the R soft-
ware (R Development Core Team., 2015). We used as input the
twenty two earliest dates (>13,000 Cal BP) for the archaeological
sites Arroyo Seco 2, Pilauco, Cerro Tres Tetas, Cueva Lago Sofıa1,
Monte Verde Component II, Tres Arroyos, Cueva del Medio,
Chinchihuapi, Los Toldos, and Piedra Museo AEP-1 (Table A.1).
Alternatively, we employed fifteen less controversial radiocarbon
dates between 11,900 and 11,000 C14 BP (13,700 and 12,900 Cal BP;
Steele and Politis, 2009) from the following sites: Tres Arroyos,
Cueva del Medio, Pilauco, Cerro La China-Sitio 2, Cerro Tres Tetas,
Arroyo Seco 2, Cueva Lago Sofıa 1, Monte Verde Component II.
2.2.2. Spatial distribution of radiocarbon dates
The spatial distribution and density of calibrated dates along
time was explored using geographic distribution maps. The sites
were geo-referenced using the Gauss Krueger projection
(Argentina), Sash 3 Datum: WGS84. We divided the dataset in pe-
riods of 2000 years and superimposed a grid of 100 100kmof
size on the maps of distribution of radiocarbon dates (Fig. 1 and
Fig. A.1). To select the size of the cells we considered that they were
not too large, resulting in excessive loss of localized information, or
too small to generate artificial spatial discontinuities in the distri-
bution of sites. The frequency of sites by period was recorded for
each cell and then plotted against the mean geographical position
of the cells. To obtain a continuous distribution of frequency values
across the entire region, we estimated the frequency of dates for
each pixel on a map of Patagonia by interpolating the observations
available in neighbor areas of the mean position of each cell using
the inverse distance-weighting approach (Legendre, 1993;
Legendre and Legendre, 1998). We set the ‘search circle’around
each pixel using a maximum of 12 neighbor cells and a minimum of
nine neighbor cells to be included in each interpolation value. For
each pixel, an estimated value (ỳ) was assigned by using the
weighted mean of the neighbor observations within the search
circle; ỳ¼Pw
i
y
i
, where y
i
is an observed value in the circle and w
i
is the inverse of the distance between the observed value and the
frequency to be estimated. This interpolation plot method gener-
ates a more robust and smooth estimation of site distribution and
has been widely applied in ecology (Legendre, 1993). The method
assumes that the estimated frequency for the pixels is likely to
resemble the frequencies of the cells of the same local area, and that
the differences in the frequency of sites among cells are in an in-
verse proportion to the distance between them.
For each period, we also estimated the distribution of distances
from each site to the sea coast dpast and present coastlinedas
Euclidean distances considering a variable search radius. All the
analyses were performed in the Quantum GIS v2.8.5 software (QGIS
Development Team, 2015).
2.2.3. Temporal distribution of radiocarbon dates
To explore the pattern of temporal changes in the occupation of
Patagonia we employed time distribution graphs (Surovell and
Brantingham, 2007; Williams, 2012; Shennan et al., 2013). Specif-
ically, the calibrated dates were graphed using histograms to
generate curves of densities of occupation throughout time, which
indirectly allowed us to explore temporal changes in human
demography. The radiocarbon dates were ‘data binned’into 400
year intervals to reduce the effect of sampling bias. We considered
the impact of type of archeological site, a taphonomic factor that
might have an effect on the density curves of radiocarbon dates, by
estimating the temporal distribution of open air, rockshelter and
cave sites. We also corrected the number of dates at each time in-
terval tby dividing the observed number of dates in each interval
by the empirically derived expectations suggested by Surovell et al.
(2009; S2009), where the expected nt ¼5.726442 10
6
(t þ2176.4)
1.3925309
. The distribution of temporal frequencies of
radiocarbon dates was smoothed by the common and simple n-
point centered moving average, with a nvalue of five (Hammer and
Harper, 2006).
S.I. Perez et al. / Quaternary International 425 (2016) 214e223216
Finally, to test if the trend observed in the distribution of
radiocarbon dates was positive and significant we applied the
non-parametric ManneKendall test (Gilbert, 1987). The S statistic
was calculated by summing over all pairs of values,
S¼P
n1
i¼1
P
n
j¼iþ1
sgn ðxj xiÞ. The sign of the S value is informative
of the sign of the trend. The significance of S was established using
the Z statistic. The statistical analyses were performed in PAST v.
3.09 (Hammer et al., 2001) and R software 3.0.3 (R Development
Core Team., 2015).
2.3. Molecular-based analyses
2.3.1. Time of coalescence and demographic inference
The molecular sequences were used to estimate the time of
coalescence of haplotype mtDNA lineages and demographic tra-
jectories of human populations from Patagonia employing Bayesian
methods (Drummond et al., 2005, 2006). We estimated genealog-
ical trees with time of divergence by haplotypes using the method
developed by Drummond et al. (2006). We employed a relaxed
molecular clock model, which allows substitution rates to vary
across lineages according to an uncorrelated lognormal distribution
(Drummond et al., 2006), and set the tree priors as a Yule Process.
The Bayesian Skyline Plot method (BSP; Drummond et al., 2005)
was used to estimate changes in population size along Late Pleis-
tocene and Holocene. This method uses the coalescent theory to
relate the shape of a molecular genealogy to the demographic dy-
namic of the populations in the past (Drummond et al., 2005; Ho
and Shapiro, 2011).
We generated the genealogical tree and the Skyline Plot using
the Bayesian approach implemented in BEAST 1.6.1 (Drummond
and Rambaut, 2007), which uses a Markov chain Monte Carlo
(MCMC) sampling procedure to estimate the genealogy, coales-
cence time and the population size das well as its credibility
intervalsdthrough time from the molecular sequences
(Drummond et al., 2005, 2006). The MCMC simulations were set in
50, 000, 000 generations and a sample frequency of 5000 (Rambaut
and Drummond, 2007). The BSP analyses and genealogical esti-
mations were performed assuming a HKY model of mtDNA
sequence evolution and rates of substitutions by site by year of
2.4E-7 and 3.02E-7 (s/s/y; Santos et al., 2005; Endicott and Ho,
2008; de Saint Pierre et al., 2012a, 2012b; Perez et al., 2016). We
employed Tracer v1.5 (Rambaut and Drummond, 2007) to evaluate
convergence in the MCMC simulations and to generate the BSP plot.
The genealogies were explored with the software FigTree v.1.4.
3. Results
3.1. Time of the earliest peopling
Based on radiocarbon dates and Confidence Intervals on Strati-
graphic Range analyses, we suggest that the most probable time
(i.e. the 95% confidence interval) for the earlier peopling of Pata-
gonia was between 16,000 and 13,000 years ago or between 18,000
and 14,000 years ago, considering a minimum age of either 13,000
or 14,000 Cal BP, respectively, and 14 or 16 strata (Fig. 2). The most
ancient value increase or decrease according to the amount of
archaeological strata considered in the analysis (Fig. 2). The results
obtained with the Saltr
e et al. (2015) approach also suggest an
initial peopling between 18,000 and 14,000 Cal BP (Table 1). This
time exceeds the previous evidence based on the first occurrence of
archaeologically well-supported dates, around 14,000 and
13,000 years ago (Steele and Politis, 2009; Prates et al., 2013).
Cal BP
First date: 14,000 cal BP
13,000
14,000
15,000
16,000
17,000
18,000
19,000
10 12 14 16 18 20
95% conf
Cal BP
Strata
14,000
15,000
16,000
17,000
18,000
19,000
20,000
10 12 14 16 18 20
95% con
f
Strata
First date: 13,000 cal BP
Fig. 2. Estimated age for the first peopling of Patagonia based on Confidence Intervals on Stratigraphic Range method. The upper panel shows the estimations based on an ancient
age of 14,000 Cal BP, while the lower panel displays the results obtained for the most accepted date of 13,000 Cal BP (Steele and Politis, 2009). The most probable age was estimated
considering a range of strata values between 10 and 20.
S.I. Perez et al. / Quaternary International 425 (2016) 214e223 217
Interestingly, our earlier estimation based on radiocarbon dates
is within the range of results obtained with molecular data
(Table 2). In Table 2 we show the Time of the Most Recent Common
Ancestor of the lineages B2l, C1b13, D1g and D4h3a5, that previous
studies suggest were originated within Patagonia (Bodner et al.,
2012; de Saint Pierre et al., 2012a). Because there is no agreement
about the most adequate substitution rate, we compared the ages
obtained with two different rates [2.4E-7 (Santos et al., 2005) and
3.02E-7 (Endicott and Ho, 2008) s/s/y]. Taking the substitution rate
from Santos et al. (2005) we obtained the most ancient ages of
17,266 and 15,632 years for C1b13 and D1g, respectively. The
haplotypes B2l and D4h3a5 display younger ages, of 13,674 and
10,852 years, respectively. The estimations using the Endicott and
Ho (2008) rates were in average 3000 younger (Table 2). There-
fore, these results suggest that the region was peopled between
17,000 and 14,500 years ago, considering the probable time interval
of the earliest lineage divergence within the region (the C1b13
haplotype).
3.2. Pattern of spatial occupation
Fig. 3 displays the temporal changes in the density of radio-
carbon dates, as indirect evidence of human occupation, using
artificial intervals of 2000 years. The patterns of spatial occupation
along time do not show simple latitudinal or longitudinal
trends. During the period 16,000e14,000 years, the sites were
concentrated in the Pacific coast, considering the unique evidence
of sites in the Monte Verde locality. In the next period,
14,000e12,000 years ago, additionally to the Pacific occupation, the
Atlantic coast displays evidence of occupation, particularly in
Southeast Pampa, Northeast of Santa Cruz and in both sides of the
Magellan strait (Fig. 3). During the next periods (between 12,000
and 8000 years) the interior of the continent began to be peopled,
being the first evidence found in Northwest Patagonia and the
Central Plain in Santa Cruz. Between 8000 and 4000 years ago, the
human population started to occupy the southernmost part of
Andean mountains and the density of occupation in Tierra del
Fuego increased. In the last 4000 years all the Atlantic coast was
occupied and the density of sites increased significantly across
Patagonia. Only the Central Plain of Chubut, the Central Pampa and
the Somuncur
a Plain in Río Negro show low density of sites during
all periods.
The distribution of distances to the sea shows that during the
early peopling almost all sites were closer than 150 km to either the
Atlantic or Pacific sea (Atlantic and Pacific; Fig. A.2). During the Late
Pleistocene and Early Holocene (12,000e8000 years BP) the sites
were homogeneously distributed between 0 and 350 km from the
sea. After 8000 years BP and during the Middle and Late Holocene
the sites were concentrated in the coast, between 20 or 30 km to
the sea (Fig. A.2).
3.3. Demographic changes
The ManneKendall test shows that the positive trend observed
in the distribution of radiocarbon dates for all types of sites is sig-
nificant (Cave: S ¼
505, P <0.0001; Rockshelter: S ¼582,
P<0.0001; Open air: S ¼648, P <0.0001). Fig. 4 displays the
demographic reconstruction based on calibrated radiocarbon dates
for the different types of sites using data uncorrected and the S2009
correction for taphonomic bias. The curve estimated using cave
dates displays an increase in population size between 14,000 and
12,500 years ago, then no changes in population size are observed
until 4000 years ago, when a steady increase occurs (Fig. 4). Un-
corrected rockshelter and open air sites only display an increase in
population size around 4000 years ago. However, the use of the
correction method proposed by Surovell et al. (2009; S2009) results
in a curve more similar to that obtained with the cave data (Fig. 4).
Interestingly, this correction generates more sudden fluctuations in
the frequency of sites than the uncorrected data, as can be seen, for
instance, around 10,200 and 3500 years BP. Such fluctuations are
probably related to sampling bias of radiocarbon dates (Perez et al.,
2016).
The Bayesian Skyline plot (BSP) based on molecular data shows
that the human population from Patagonia had a female effective
population size of ca. 1200 individuals during the Late Pleistocene,
16,000 years ago, and it increased slowly between 12,500 and
6000 years ago, being this change more noticeable after
7000e500 0 years ago (Fig. 5). The population reached an estimated
female effective population size of 10,500 individuals ca.
2500 years ago. Then, it continued growing until reaching a size of
20,000 individuals ca. 500 years ago. The confidence intervals
generated by the BSP progressively increase from 350 to 7000 in-
dividuals by 16,000 years BP to 7000e70,000 individuals by 500
years ago (Fig. 5).
4. Discussion
In this work we present an analysis of an extensive dataset of
published radiocarbon dates from recently excavated archaeolog-
ical sites and mtDNA sequences of modern and ancient aboriginal
populations from Patagonia, southern South America. To the best of
our knowledge, this is the first study that comprehensively explores
the time of peopling, the spatial occupation and changes in human
demography in Patagonia. These problems have been mainly
addressed using radiocarbon dates only at regional scales (Martínez
et al., 2013), or datasets restricted to Late Pleistocene and Early
Table 1
Estimated interval for the earlier Patagonian peopling based on the approaches of Strauss and Sadler (1989), Marshall (1997) and GRIWM (Bradshaw et al., 2012), using the
most conservative and the more controversial radiocarbon dates (Steele and Politis, 2009).
Method Dates >13,000 Cal BP Dates >11,000 and <12,000 C14 BP
Calibrated younger age Calibrated oldest age Calibrated younger age Calibrated oldest age
Strauss-Sadler 16,289 16,795 13,658 13,880
Marshall 16,283 18,433 13,657 14,471
Griwm 17,031 17,044 14,036 14,042
Table 2
Coalescence ages of the mtDNA variants (haplotypes) with high frequencies and/or
mainly restricted to populations from the extreme south of South America. The ages
were calculated using two different mutation rates, Endicott and Ho (2008; 1) and
Santos et al. (2005; 2).
Mutational rates
Haplotypes 0.302 s/s/y
2
0.24 s/s/y
3
B2l 10,872 13,674
C1b13 14,522 17,266
D1g 12,120 15,632
D4h3a5 7848 10,852
S.I. Perez et al. / Quaternary International 425 (2016) 214e223218
Fig. 3. Spatial patterns of the frequency of sites in Patagonia. The map of the density of
sites was created for eight temporal intervals using interpolating methods with the
inverse distance-weighting approach.
Cave
0 5000 10000 15000
0 5000 10000 15000
Rockshelter
Standarized Frequency
0.06
0.12
0.18
0.24
0.30
0.36
0.42
0.48
0.54
Cal BP
0 5000 10000 15000
Open air
S2009
uncorrected
0.00
0.08
0.16
0.24
0.32
0.40
0.48
0.56
0.64
0.72
Standarized Frequency
0.00
0.00
0.08
0.16
0.24
0.32
0.40
0.48
0.56
0.64
Standarized Frequency
S2009
uncorrected
uncorrected
Fig. 4. Demographic reconstructions based on calibrated radiocarbon dates of caves,
rocksettlers and open air sites. For the last two types of sites, the estimations using
corrected data for taphonomic bias with the method of Surovell et al. (2009; S2009)
are also shown.
S.I. Perez et al. / Quaternary International 425 (2016) 214e223 219
Holocene periods (Miotti and Salemme, 2003; Steele and Politis,
2009; Prates et al., 2013).
The confidence intervals obtained for the earliest and strongly
supported radiocarbon dates, as well as the estimation of the time
of the most recent common ancestor of the mtDNA lineages specific
of Patagonia, suggest that the initial peopling of the region occurred
between 17,000 and 14,000 years ago. Previous analyses of mito-
chondrial lineages exclusively distributed in southern South
America (Bodner et al., 2012;de Saint Pierre et al., 2012a) agree
with our results. Particularly, these studies show that some hap-
lotypes such as B2l, C1b13 and D1g dwhich present large variation,
have high frequencies in current populations, are observed in
ancient DNA and are mainly restricted to populations from the
extreme south of South Americadhave a range of ages between
19,000 and 14,000 years ago, when the substitution rates employed
in our work are used, or are even much older when considering the
substitution rate suggested by Soares et al. (2009). We estimate
similar ages employing a more comprehensive dataset of se-
quences, showing that these estimations are very robust. Interest-
ingly, this estimation agrees with the controversial dates of the
archaeological site Monte Verde (Chile), whose Component II has
calibrated dates between 18,500 and 14,500 Cal BP (Dillehay et al.,
2015), as well as with Piedra Museo and Pilauco with dates around
15,000 Cal BP (Miotti et al., 1999; Pino et al., 2013). However, our
results cannot be interpreted as evidence supporting theveracity of
the earliest radiocarbon dates from those archaeological sites.
Our estimations of the earliest peopling event are outside of the
values presented by most archaeological studies. Particularly, Steele
and Politis (2009) suggest, based on samples with strong anthropic
evidence (hearth charcoal and cut-marked bone), that human
populations were in the southern cone of South America at or soon
after 13,000 Cal BP. They suggest that this is the time of funding of
“a persistent and demographically viable hunter-gatherer popula-
tion”(Steele and Politis, 2009). However, the evidence analyzed
here suggest that the human population of Patagonia was experi-
encing a demographic growth by that time, remaining then rela-
tively stable until the end of the Middle Holocene (Figs. 4 and 5).
Therefore, the apparent discrepancies between the ages suggested
by recent archaeological studies and the estimations obtained here
can be solved if we consider that the interval between our earliest
dates and the first population growth dthe time of peopling sup-
ported by Steele and Politis (2009)dwas probably the time of the
initial spreading of humans in a previously empty area (Borrero,
1994e1995), where the chances of finding archaeological remains
are very low.
After 13,000 Cal BP, radiocarbon dates and molecular data sug-
gest that Patagonia was stably occupied by a human population that
grew slowly. Radiocarbon dates for cave sites show this pattern
more clearly. The radiocarbon distributions of the rockshelter and
open air sites after taphonomic correction suggest a similar pattern.
However, some peaks and valleys observed in the open air and
rockshelter distributions of radiocarbon dates should be inter-
preted with caution, specifically the peak around 12,500 Cal BP in
the rockshelter distribution and the peak around 7500 Cal BP in the
open air data (Fig. 4), because they can be the result of over-
correction of the S2009 formulae (Williams, 2013). Even consid-
ering the limitations of the different datasets and corrections, the
results for the population changes along Late Pleistocene and Early
Holocene are generally concordant. Our results also show that
although the population grew constantly along the Holocene, the
largest population increase began after 7000e5000 Cal BP, reach-
ing the maximum size at 1000 Cal BP (Figs. 4 and 5). For the Late
Holocene we estimated a population density between 5 and 20
individuals/100 km2, which represents a 30 fold increase compared
to the density calculated for the Late Pleistocene. Importantly, this
trend can be observed in molecular, and also in the S2009 corrected
and uncorrected radiocarbon data, indicating that the pattern of
population growth during the Late Holocene is not a result of
taphonomic effects or other biases. The rapid increase in the pop-
ulation of Patagonia can be seen more clearly in radiocarbon data.
Along with the demographic changes that took place during the
Late Holocene, there was an increasing use of landscapes previously
empty, suggesting that this was a period of intensification in the
human occupation and use of resources, i.e., the effective occupa-
tion phase described in previous studies (Borrero, 1989e1990,
1994e1995). During this time of rapid population growth, the hu-
man settlements were increasingly concentrated in the coast of the
sea, between zero and 30 km (Fig. 3 and Fig. A.2). This spatial
pattern strongly contrasts with the spatial distribution of sites
during the Late Pleistocene and Early Holocene, when a high
Years BP
0 2500 5000 7500 10000 12500 15000
35
350
3,500
35,000
350,000
Female Effective Population Size
Fig. 5. BSP reconstruction of the human demographic curve based on modern and ancient mtDNA control region. The analysis was performed using the sequences from de-
scendants of aboriginal populations of Patagonia having mtDNA variants (haplotypes) with high frequencies and/or mainly restricted to the extreme south of South America.
S.I. Perez et al. / Quaternary International 425 (2016) 214e223220
frequency of sites was found at distances between 50 and 150 km
from the coast of the sea. Such distance to the coast suggests that
human groups were not occupying the coast intensively. Whether
these patterns are related to real population processes or are the
result of supra-regional taphonomic factors related to changes in
the level of the sea is a problem that requires future investigations.
Moreover, some regions in the interior of the continent, as the
Northeast of Santa Cruz and the North of Neuqu
en and South of
Mendoza, have little evidence of human occupation during the
Middle Holocene. The finding that the population size of Patagonia
increased constantly along the from Early to Late Holocene sup-
ports the hypothesis that the lack of evidence of occupation in such
areas could be related to local depopulation and human mobiliza-
tion to other places rather than population extinction (Salemme
and Miotti, 2008).
Other areas, by contrast, remained empty during the elapsed
time since the initial peopling. This is the case for the South of Rio
Negro, the central area of Chubut and the center-south of La Pampa
(Fig. 3). The lack of radiocarbon dates in those areas could be the
result of either the lack of research or the scarcity of resources for
sustaining higher population densities. The latter option is the most
probable given that these areas have been as studied as others with
high frequency of dates (Miotti et al., 2009; Ber
on, 2015), and the
fact that they are characterized by a limited availability of fresh-
water. Particularly, the distribution of archaeological sites along the
Late PleistoceneeHolocene shows that almost all sites are at less
than 100 km close to the nearest river, being between 60% and 80%
of sites at a shorter distance than 10 km to a permanent river
(Figs. A.3 and A.4). Therefore, a strong dependence between the
pattern of human occupation and the distribution of freshwater
resources is observed in Patagonia.
The pattern of changes in population size and spatial dispersion
since the initial peopling can be interpreted in light of the general
patterns of association between population density and subsistence
strategies of hunter-gatherers. Zoo-archaeological evidence sug-
gests that the early spread of humans in southern South America
was supported by the relatively high availability of large and mega-
fauna, mainly species of Lama and Rhea, but also Hippidion and
Mylodon (Borrero, 2009; Pires et al., 2016). The initial changes in
population size could be related to the demographic growth of the
largest survival large-herbivore, the guanaco (Pires et al., 2016).
Pires and collaborators (2016) show that ca. 8000 Cal BP, after the
megafaunal extinction, populations of guanacos (Lama guanicoe)
grew fast, suggesting that the density of the humans dits main
predatordwas coupled with the guanaco demography. In this way,
numerous evidence shows that guanaco was the main prey of
Patagonian hunter-gatherers (Mengoni Go~
nalons, 1999; Miotti and
Salemme, 1999; Pires et al., 2016). Moreover, the steepest growth
during the Late Holocene period appears to be also related to the
intensification in the occupation and use of resources along almost
all the coast of Pampa and Patagonia.
The increase in population density (beyond a packing threshold
of 9.1 individuals/100 km2) among contemporary hunter-gatherers
is only observed when intensification strategies are developed,
varying according to the effective temperature and the availability
of aquatic resources (Binford, 2001; Johnson, 2014). It is remarkable
that the packing threshold of 9.1 individuals/100 km2 was probably
over-passed in Patagonia during the Late Holocene. Isotopic and
zoo-archaeological evidence show that the Late Holocene is char-
acterized by a process of diversification in the subsistence strate-
gies and diet intensification, including the incorporation of small
animals and vegetables in Northwest Patagonia and South Cuyo (Gil
et al., 2011; Gord
on et al., 2016), the incorporation of a large di-
versity of aquatic resources along the coast (mollusks, fishes and
pinnipeds; Zangrando, 2009; Stoessel and Martínez, 2014) and new
labour investment in food processing (Stoessel and Martínez, 2014).
Particularly, an increase in the consumption of marine resources is
simultaneously found between 7500 and 6000 Cal BP in different
areas of the Atlantic coast, such as North of Chubut and Santa Cruz
provinces, Río Negro and Tierra del Fuego (G
omez Otero, 2006;
Zangrando, 2009; Favier Dubois and Scartascini, 2012; Zubimendi
et al., 2015). It is worth noting that close dates were obtained
here for the beginning of the demographic increase in Patagonia.
The population growth in the Middle and Late Holocene is also
associated with changes in technology. Particularly, this period is
characterized by the development of new technologies for
obtaining (e.g. bow and arrow) and processing food (e.g. pottery
and mortars; Politis et al., 2001; Stoessel and Martínez, 2014). The
processes of intensification in the use of resources and technolog-
ical change may have begun during the Middle Holocene (ca.
5000e400 0 Cal BP) in Northwest Patagonia and South Cuyo, where
domesticated plants were also incorporated (Fernandez,
1988e1990; Gil et al., 2006). In South Pampa and the Central
coast of Patagonia, the process of intensification probably occurred
after 3000 Cal BP (Martínez, 1999; Favier Dubois et al., 2009). In
other areas, as in the coast of North Patagonia and Tierra del Fuego,
the process may have begun much later, after 1000 Cal BP
(Zangrando, 2009; Stoessel and Martínez, 2014). These results
suggest that the processes of population growth and intensification
in the use of resources were not homogeneous and simultaneous
across Patagonia. Moreover, the archaeological evidence for the
later Late Holocene sites is consistent with a reduction in resi-
dential mobility and the development of logistic mobility strategies
(Go~
ni, 2010; Martínez, 2008e2009).
5. Conclusions
In sum, this study provides a well-supported pattern of the
peopling and demographic evolution of aboriginal populations of
Patagonia, which suggests that the colonization and posterior de-
mographic expansion occurred earlier than generally postulated.
Our results indicate a scenario in which Patagonia was peopled by
small groups that arrived to the region between 17,000 and
14,000 Cal BP. At a regional scale, these populations experienced a
sustained and slow growth until 7000e5000 Cal BP, when a rapid
demographic expansion took place reaching its maximum at
1000 Cal BP. However, this process was not spatially homogeneous.
The initial peopling followed the Atlantic and Pacific coasts, while
the interior was more intensively occupied along the Pleistoce-
neeHolocene transition and the Early Holocene. By the Middle
Holocene, this trend started to be reversed and the occupation of
the coast increased remarkably, while other areas remained unin-
habited until the Late Holocene. The pattern outlined here, ob-
tained on the basis of rigorous quantitative approaches, will allow
the future evaluation of formal models about the ecological and
cultural processes that drove the evolution of the human pop-
ulations from Patagonia.
Acknowledgement
This work was supported by grants from FONCyT (“Din
amica
poblacional humana y variaci
on en el nicho ecol
ogico en el Nor-
oeste de Patagonia durante el Holoceno.”PICT 2014/2017e2134),
CONICET (“Din
amica poblacional humana y cambios en el nicho
ecol
ogico en el Noroeste de Patagonia durante el Holoceno. PIP 729-
2015e2017) and Universidad Nacional de La Plata (“Ecología y
evoluci
on de las poblaciones humanas del Noroeste de Patagonia
(Pcia. del Neuqu
en) durante el Holoceno.”UNLP. 2016e2019).
S.I. Perez et al. / Quaternary International 425 (2016) 214e223 221
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.quaint.2016.05.004.
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