El Niño's role in changing fauna.

Past faunas show how El Niño frequency affects eastern Pacific community structure.

Response to comment on "Evidence of prehistoric human activity in the Falkland Islands".

Hamley et al. previously presented multiple lines of evidence that people were present in the Falkland Islands before Europeans and may have brought the now-extinct canid, Dusicyon australis. Stable isotope data reported by Clark et al. indicate that D. australis had a high-trophic, marine diet that terrestrialized following European arrival. This is consistent with our hypothesis of a human mutualism.

The earliest adobe monumental architecture in the Americas.

Adobe bricks, or mud bricks, are construction elements which have defined major architectural traditions in the Andes over thousands of years. From Moche pyramids and the ancient city of Chan Chan in pre-Hispanic times, to Spanish casonas of the colonial period and rural houses in contemporary South America, adobe has been a central component in Andean architecture. Discovery of the remains of an early monumental building constructed primarily of adobes at Los Morteros (lower Chao Valley, north coast of Peru) places the invention of adobe architecture before 5,100 calendar years B.P. The unique composition, internal structure, and chronology of the adobes from Los Morteros show the beginnings of this architectural technique, which is associated with El Niño rainfall and the construction of the earliest adobe monumental building in the Americas. We propose that adobe architecture became a major Andean tradition after a long period of technical evolution and experimentation with both shape and composition.

Evidence of prehistoric human activity in the Falkland Islands.

When Darwin visited the Falkland Islands in 1833, he noted the puzzling occurrence of the islands' sole terrestrial mammal, Dusicyon australis (or "warrah"). The warrah's origins have been debated, and prehistoric human transport was previously rejected because of a lack of evidence of pre-European human activity in the Falkland Islands. We report several lines of evidence indicating that humans were present in the Falkland Islands centuries before Europeans, including (i) an abrupt increase in fire activity, (ii) deposits of mixed marine vertebrates that predate European exploration by centuries, and (iii) a surface-find projectile point made of local quartzite. Dietary evidence from D. australis remains further supports a potential mutualism with humans. The findings from our study are consistent with the culture of the Yaghan (Yámana) people from Tierra del Fuego. If people reached the Falkland Islands centuries before European colonization, this reopens the possibility of human introduction of the warrah.

Population density and size facilitate interactive capacity and the rise of the state.

Radiocarbon summed probability distribution (SPD) methods promise to illuminate the role of demography in shaping prehistoric social processes, but theories linking population indices to social organization are still uncommon. Here, we develop Power Theory, a formal model of political centralization that casts population density and size as key variables modulating the interactive capacity of political agents to construct power over others. To evaluate this argument, we generated an SPD from 755 radiocarbon dates for 10 000-1000 BP from Central, North Central and North Coast Peru, a period when Peruvian political form developed from 'quasi-egalitarianism' to state levels of political centralization. These data are congruent with theoretical expectations of the model but also point to an artefactual distortion previously unremarked in SPD research. This article is part of the theme issue 'Cross-disciplinary approaches to prehistoric demography'.

Leveraging legacy archaeological collections as proxies for climate and environmental research.

Understanding the causes and consequences of previous climate changes is essential for testing present-day climate models and projections. Archaeological sites are paleoenvironmental archives containing unique ecological baselines with data on paleoclimate transformations at a human timescale. Anthropogenic and nonanthropogenic forces have destroyed many sites, and others are under immediate threat. In the face of this loss, previously excavated collections from these sites-referred to as legacy collections-offer a source of climate and other paleoenvironmental information that may no longer exist elsewhere. Here, we 1) review obstacles to systematically using data from legacy archaeological collections, such as inconsistent or unreported field methods, inadequate records, unsatisfactory curation, and insufficient public knowledge of relevant collections; 2) suggest best practices for integrating archaeological data into climate and environmental research; and 3) summarize several studies to demonstrate the benefits and challenges of using legacy collections as archives of local and regional environmental proxies. Data from archaeological legacy collections contribute regional ecological baselines as well as serve to correct shifting baselines. They also enable regional climate reconstructions at various timescales and corroborate or refine radiocarbon dates. Such uses of legacy collections raise ethical concerns regarding ownership of and responsibility for cultural resources and highlight the importance of Indigenous involvement in planning and executing fieldwork and stewardship of cultural heritage. Finally, we discuss methodologies, practices, and policies pertaining to archaeological legacy collections and support calls for discipline-wide shifts in collections management to ensure their long-term utility in multidisciplinary research and public engagement.

Archaeological climate proxies and the complexities of reconstructing Holocene El Niño in coastal Peru.

Archaeological evidence plays a key role in longitudinal studies of humans and climate. Climate proxy data from Peruvian archaeological sites provide a case study through insight into the history of the "flavors" or varieties of El Niño (EN) events after ∼11 ka: eastern Pacific EN, La Niña, coastal EN (COA), and central Pacific or Modoki EN (CP). Archaeological proxies are important to the coastal Peruvian case because more commonly used paleoclimate proxies are unavailable or equivocal. Previously, multiproxy evidence from the Peruvian coast and elsewhere suggested that EN frequency varied over the Holocene: 1) present in the Early Holocene; 2) absent or very low frequency during the Middle Holocene (∼9 to 6 ka); 3) low after ∼6 ka; and 4) rapidly increasing frequency after 3 ka. Despite skepticism about the reliability of archaeological proxies, nonarchaeological proxies seemed to confirm this archaeological EN reconstruction. Although there is consensus that EN frequency varied over this period, some nonarchaeological and archaeological proxies call parts of this reconstruction into question. Here we review Holocene EN frequency reconstructions for the Peruvian coast, point to complexities introduced by apparent contradictions in a range of proxy records, consider the impact of CP and COA phenomena, and assess the merits of archaeological proxies in EN reconstructions. Reconciling Peruvian coastal paleoclimate data is critical for testing models of future EN behavior under climate variability.

Archaeology, climate, and global change in the Age of Humans.

We live in an age characterized by increasing environmental, social, economic, and political uncertainty. Human societies face significant challenges, ranging from climate change to food security, biodiversity declines and extinction, and political instability. In response, scientists, policy makers, and the general public are seeking new interdisciplinary or transdisciplinary approaches to evaluate and identify meaningful solutions to these global challenges. Underrecognized among these challenges is the disappearing record of past environmental change, which can be key to surviving the future. Historical sciences such as archaeology access the past to provide long-term perspectives on past human ecodynamics: the interaction between human social and cultural systems and climate and environment. Such studies shed light on how we arrived at the present day and help us search for sustainable trajectories toward the future. Here, we highlight contributions by archaeology-the study of the human past-to interdisciplinary research programs designed to evaluate current social and environmental challenges and contribute to solutions for the future. The past is a multimillennial experiment in human ecodynamics, and, together with our transdisciplinary colleagues, archaeology is well positioned to uncover the lessons of that experiment.

Suicides as a response to adverse market sentiment (1980-2016).

Financial crises inflict significant human as well as economic hardship. This paper focuses on the human fallout of capital market stress. Financial stress-induced behavioral changes can manifest in higher suicide and murder-suicide rates. We find that these rates also correlate with the Gross Domestic Product (GDP) growth rate (negatively associated; a -0.25% drop [in the rate of change in annual suicides for a +1% change in the independent variable]), unemployment rate (positive link; 0.298% increase), inflation rate (positive link; 0.169% increase in suicide rate levels) and stock market returns adjusted for the risk-free T-Bill rate (negative link; -0.047% drop). Suicides tend to rise during periods of economic turmoil, such as the recent Great Recession of 2008. An analysis of Centers for Disease Control and Prevention (CDC) data of more than 2 million non-natural deaths in the US since 1980 reveals a positive correlation with unemployment levels. We find that suicides and murder-suicides associated with adverse market sentiment lag the initial stressor by up to two years, thus opening a policy window for government/public health intervention to reduce these negative outcomes. Both our models explain about 73 to 76% of the variance in suicide rates and rate of change in suicide rates, and deploy a total of four widely available independent variables (lagged and/or transformed). The results are invariant to the inclusion/exclusion of 2008 data over the 1980-2016 time series, the period of our study. The disconnect between rational decision making, induced by cognitive dissonance and severe financial stress can lead to suboptimal outcomes, not only in the area of investing, but in a direct loss of human capital. No economic system can afford such losses. Finance journal articles focus on monetary alpha, which is the return on a portfolio in excess of the benchmark; we think it is important to be aware of the loss of human capital as a consequence of market instability. This study makes one such an attempt.

Paleoindian settlement of the high-altitude Peruvian Andes.

Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival. The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions, hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the initial entry of humans to South America.

Effect of the Spanish Conquest on coastal change in Northwestern Peru.

When Francisco Pizarro and his small band of Spanish conquistadores landed in northern Peru in A.D. 1532 to begin their conquest of the vast Inca Empire, they initiated profound changes in the culture, language, technology, economics, and demography of western South America. They also altered anthropogenically modulated processes of shoreline change that had functioned for millennia. Beginning with the extirpation of local cultures as a result of the Spanish Conquest, and continuing through today, the intersection of demography, economy, and El Niño-driven beach-ridge formation on the Chira beach-ridge plain of Northwestern Peru has changed the nature of coastal evolution in this region. A similar event may have occurred at about 2800 calibrated y B.P. in association with increased El Niño frequency.

El Niño impact on mollusk biomineralization-implications for trace element proxy reconstructions and the paleo-archeological record.

Marine macroinvertebrates are ideal sentinel organisms to monitor rapid environmental changes associated with climatic phenomena. These organisms build up protective exoskeletons incrementally by biologically-controlled mineralization, which is deeply rooted in long-term evolutionary processes. Recent studies relating potential rapid environmental fluctuations to climate change, such as ocean acidification, suggest modifications on carbonate biominerals of marine invertebrates. However, the influence of known, and recurrent, climatic events on these biological processes during active mineralization is still insufficiently understood. Analysis of Peruvian cockles from the 1982-83 large magnitude El Niño event shows significant alterations of the chemico-structure of carbonate biominerals. Here, we show that bivalves modify the main biomineralization mechanism during the event to continue shell secretion. As a result, magnesium content increases to stabilize amorphous calcium carbonate (ACC), inducing a rise in Mg/Ca unrelated to the associated increase in sea-surface temperature. Analysis of variations in Sr/Ca also suggests that this proxy should not be used in these bivalves to detect the temperature anomaly, while Ba/Ca peaks are recorded in shells in response to an increase in productivity, or dissolved barium in seawater, after the event. Presented data contribute to a better understanding of the effects of abrupt climate change on shell biomineralization, while also offering an alternative view of bivalve elemental proxy reconstructions. Furthermore, biomineralization changes in mollusk shells can be used as a novel potential proxy to provide a more nuanced historical record of El Niño and similar rapid environmental change events.

Environmental change and economic development in coastal Peru between 5,800 and 3,600 years ago.

Between approximately 5,800 and 3,600 cal B.P. the biggest architectural monuments and largest settlements in the Western Hemisphere flourished in the Supe Valley and adjacent desert drainages of the arid Peruvian coast. Intensive net fishing, irrigated orchards, and fields of cotton with scant comestibles successfully sustained centuries of increasingly complex societies that did not use ceramics or loom-based weaving. This unique socioeconomic adaptation was abruptly abandoned and gradually replaced by societies more reliant on food crops, pottery, and weaving. Here, we review evidence and arguments for a severe cycle of natural disasters-earthquakes, El Niño flooding, beach ridge formation, and sand dune incursion-at approximately 3,800 B.P. and hypothesize that ensuing physical changes to marine and terrestrial environments contributed to the demise of early Supe settlements.

Starch fossils and the domestication and dispersal of chili peppers (Capsicum spp. L.) in the Americas.

Chili peppers (Capsicum spp.) are widely cultivated food plants that arose in the Americas and are now incorporated into cuisines worldwide. Here, we report a genus-specific starch morphotype that provides a means to identify chili peppers from archaeological contexts and trace both their domestication and dispersal. These starch microfossils have been found at seven sites dating from 6000 years before present to European contact and ranging from the Bahamas to southern Peru. The starch grain assemblages demonstrate that maize and chilies occurred together as an ancient and widespread Neotropical plant food complex that predates pottery in some regions.

Early maize agriculture and interzonal interaction in southern Peru.

Over the past decade, increasing attention to the recovery and identification of plant microfossil remains from archaeological sites located in lowland South America has significantly increased knowledge of pre-Columbian plant domestication and crop plant dispersals in tropical forests and other regions. Along the Andean mountain chain, however, the chronology and trajectory of plant domestication are still poorly understood for both important indigenous staple crops such as the potato (Solanum sp.) and others exogenous to the region, for example, maize (Zea mays). Here we report the analyses of plant microremains from a late preceramic house (3,431 +/- 45 to 3,745 +/- 65 14C bp or approximately 3,600 to 4,000 calibrated years bp) in the highland southern Peruvian site of Waynuna. Our results extend the record of maize by at least a millennium in the southern Andes, show on-site processing of maize into flour, provide direct evidence for the deliberate movement of plant foods by humans from the tropical forest to the highlands, and confirm the potential of plant microfossil analysis in understanding ancient plant use and migration in this region.

An Asian origin for a 10,000-year-old domesticated plant in the Americas.

New genetic and archaeological approaches have substantially improved our understanding of the transition to agriculture, a major turning point in human history that began 10,000-5,000 years ago with the independent domestication of plants and animals in eight world regions. In the Americas, however, understanding the initial domestication of New World species has long been complicated by the early presence of an African enigma, the bottle gourd (Lagenaria siceraria). Indigenous to Africa, it reached East Asia by 9,000-8,000 before present (B.P.) and had a broad New World distribution by 8,000 B.P. Here we integrate genetic and archaeological approaches to address a set of long-standing core questions regarding the introduction of the bottle gourd into the Americas. Did it reach the New World directly from Africa or through Asia? Was it transported by humans or ocean currents? Was it wild or domesticated upon arrival? Fruit rind thickness values and accelerator mass spectrometer radiocarbon dating of archaeological specimens indicate that the bottle gourd was present in the Americas as a domesticated plant by 10,000 B.P., placing it among the earliest domesticates in the New World. Ancient DNA sequence analysis of archaeological bottle gourd specimens and comparison with modern Asian and African landraces identify Asia as the source of its introduction. We suggest that the bottle gourd and the dog, two "utility" species, were domesticated long before any food crops or livestock species, and that both were brought to the Americas by Paleoindian populations as they colonized the New World.

Otolith delta 18O record of mid-Holocene sea surface temperatures in Peru.

Peruvian sea catfish (Galeichthys peruvianus) sagittal otoliths preserve a record of modern and mid-Holocene sea surface temperatures (SSTs). Oxygen isotope profiles in otoliths excavated from Ostra [6010 +/- 90 years before the present (yr B.P.); 8 degrees 55'S] indicate that summer SSTs were approximately 3 degrees C warmer than those of the present. Siches otoliths (6450 +/- 110 yr B.P.; 4 degrees 40'S) recorded mean annual temperatures approximately 3 degrees to 4 degrees C warmer than were measured under modern conditions. Trophic level and population diversity and equitability data from these faunal assemblages and other Peruvian archaeological sites support the isotope interpretations and suggest that upwelling of the Peru-Chile current intensified after approximately 5000 yr B.P.