Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens

We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region’s past and offers a new context within which the late Holocene “Earthmovers” of the Llanos de Moxos could have emerged.

Adaptive, convergent origins of the pygmy phenotype in African rainforest hunter-gatherers

Tropical rainforest hunter-gatherer populations worldwide share the pygmy phenotype, or small human body size. The evolutionary history of this phenotype is largely unknown. Here we studied DNA from the Batwa, a rainforest hunter-gatherer population from east central Africa, to identify regions of the Batwa genome that underlie the pygmy phenotype. We then performed population genomic analyses to study the evolution of these regions, including comparisons with the Baka, a west central African rainforest hunter-gatherer population. We conclude that the pygmy phenotype likely arose due to positive natural selection and that it arose possibly multiple times within Africa. These results support longstanding anthropological hypotheses that small body size confers an important selective advantage for human rainforest hunter-gatherers.