Humans settled the Caribbean ~6,000 years ago, with ceramic use and intensified agriculture marking a shift from the Archaic to the Ceramic Age ~2,500 years ago 1 – 3 . We report genome-wide data from 174 individuals from The Bahamas, Hispaniola, Puerto Rico, Curaçao, and Venezuela co-analyzed with published data. Archaic Age Caribbean people derive from a deeply divergent population closest to Central and northern South Americans; contrary to previous work 4 , we find no support for ancestry contributed by a population related to North Americans. Archaic lineages were >98% replaced by a genetically homogeneous ceramic-using population related to Arawak-speakers from northeast South America who moved through the Lesser Antilles and into the Greater Antilles at least 1,700 years ago, introducing ancestry that is still present. Ancient Caribbean people avoided close kin unions despite limited mate pools reflecting small effective population sizes which we estimate to be a minimum of Ne=500–1500 and a maximum of Ne=1530–8150 on the combined islands of Puerto Rico and Hispaniola in the dozens of generations before the analyzed individuals lived. Census sizes are unlikely to be more than ten-fold larger than effective population sizes, so previous estimates of hundreds of thousands of people are too large 5 – 6 . Confirming a small, interconnected Ceramic Age population 7 , we detect 19 pairs of cross-island cousins, close relatives ~75 kilometers apart in Hispaniola, and low genetic differentiation across islands. Genetic continuity across transitions in pottery styles reveals that cultural changes during the Ceramic Age were not driven by migration of genetically-differentiated groups from the mainland but instead reflected interactions within an interconnected Caribbean world 1 , 8 .

Warfare was a prevalent phenomenon throughout the Andes during the Late Intermediate period (LIP; AD 1000-1450). A salient research topic within broader investigations of conflict is how populations En los Andes, la guerra fue una ocurrencia frecuente y significativa durante el período Intermedio tardío (1000-1450 dC). La adaptación de las poblaciones a la guerra continua es un tema importante dentro de las investigaciones generales sobre conflictos. Este artículo utiliza análisis estadísticos y por medio de SIG de rasgos arquitectónicos y patrones de asentamiento para reconstruir los mecanismos defensivos de 15 asentamientos fortificados en la región de Nazca, Perú. Específicamente, esta investigación evalúa cómo se emplearon las defensas artificiales (fortificaciones), la defensibilidad natural y la localización de los asentamientos para proteger a las poblaciones y los recursos críticos durante las incursiones enemigas. Los resultados

Significance Warfare and homicide are pervasive features of the human experience, yet scholars struggle to understand the conditions that promote violence. Climate and conflict research has revealed many linkages between climate change and human violence; however, studies often produce contrary findings, and the driving mechanisms remain difficult to identify. We suggest a solution is to identify conditions producing resource scarcity, which are necessarily a combination of climate and population dynamics. We examine patterns of lethal violence in the Prehispanic Andes and find that favorable climate conditions fostered rapid population growth within a circumscribed landscape, resulting in chronic warfare. Our work suggests that an increasingly unstable climate may promote future violence, where favorable climate regimes incentivize population growth and attendant resource strain.

Objectives: This study uses osteological and radiocarbon datasets combined with formal quantitative analyses to test hypotheses concerning the character of conflict in the Nasca highlands during the Late Intermediate Period (LIP, 950-1450 C.E.). We develop and test osteological expectations regarding what patterns should be observed if violence was characterized by intragroup violence, ritual conflict, intermittent raiding, or internecine warfare. Materials and methods: Crania (n = 267) were examined for antemortem and perimortem, overkill, and critical trauma. All age groups and both sexes are represented in the sample. One hundred twenty-four crania were AMS dated, allowing a detailed analysis of diachronic patterns in violence among various demographic groups. Results: Thirty-eight percent (102/267) of crania exhibit some form of cranial trauma, a significant increase from the preceding Middle Horizon era. There are distinct trauma frequencies within the three subphases of the LIP, but Phase III (1300-1450 C.E.) exhibits the highest frequencies of all trauma types. Males exhibit significantly more antemortem trauma than females, but both exhibit similar perimortem trauma rates. Discussion: There was chronic, internecine warfare throughout the Late Intermediate Period with important variations in violence throughout the three temporal phases. Evidence for heterogeneity in violent mortality shows a pattern consistent with social substitutability, whereby any and all members of the Nasca highland population were appropriate targets for lethal and sublethal violence. We argue that by testing hypotheses regarding the targets and types of conflict we are better able to explain the causes and consequences of human conflict.

The influence of climate change on civil conflict and societal instability in the premodern world is a subject of much debate, in part because of the limited temporal or disciplinary scope of case studies. We present a transdisciplinary case study that combines archeological, historical, and paleoclimate datasets to explore the dynamic, shifting relationships among climate change, civil conflict, and political collapse at Mayapan, the largest Postclassic Maya capital of the Yucatán Peninsula in the thirteenth and fourteenth centuries CE. Multiple data sources indicate that civil conflict increased significantly and generalized linear modeling correlates strife in the city with drought conditions between 1400 and 1450 cal. CE. We argue that prolonged drought escalated rival factional tensions, but subsequent adaptations reveal regional-scale resiliency, ensuring that Maya political and economic structures endured until European contact in the early sixteenth century CE.