Early Progress

Kevin Lewis

April 03, 2021

Ecological variation and institutionalized inequality in hunter-gatherer societies
Eric Alden Smith & Brian Codding
Proceedings of the National Academy of Sciences, 30 March 2021


Research examining institutionalized hierarchy tends to focus on chiefdoms and states, while its emergence among small-scale societies remains poorly understood. Here, we test multiple hypotheses for institutionalized hierarchy, using environmental and social data on 89 hunter-gatherer societies along the Pacific coast of North America. We utilize statistical models capable of identifying the main correlates of sustained political and economic inequality, while controlling for historical and spatial dependence. Our results indicate that the most important predictors relate to spatiotemporal distribution of resources. Specifically, higher reliance on and ownership of clumped aquatic (primarily salmon) versus wild plant resources is associated with greater political-economic inequality, measuring the latter as a composite of internal social ranking, unequal access to food resources, and presence of slavery. Variables indexing population pressure, scalar stress, and intergroup conflict exhibit little or no correlation with variation in inequality. These results are consistent with models positing that hierarchy will emerge when individuals or coalitions (e.g., kin groups) control access to economically defensible, highly clumped resource patches, and use this control to extract benefits from subordinates, such as productive labor and political allegiance in a patron–client system. This evolutionary ecological explanation might illuminate how and why institutionalized hierarchy emerges among many small-scale societies.

Metaphors: The evolutionary journey from bidirectionality to unidirectionality
David Gil & Yeshayahu Shen
Philosophical Transactions of the Royal Society: Biological Sciences, March 2021


Metaphors, a ubiquitous feature of human language, reflect mappings from one conceptual domain onto another. Although founded on bidirectional relations of similarity, their linguistic expression is typically unidirectional, governed by conceptual hierarchies pertaining to abstractness, animacy and prototypicality. The unidirectional nature of metaphors is a product of various asymmetries characteristic of grammatical structure, in particular, those related to thematic role assignment. This paper argues that contemporary metaphor unidirectionality is the outcome of an evolutionary journey whose origin lies in an earlier bidirectionality. Invoking the Complexity Covariance Hypothesis governing the correlation of linguistic and socio-political complexity, the Evolutionary Inference Principle suggests that simpler linguistic structures are evolutionarily prior to more complex ones, and accordingly that bidirectional metaphors evolved at an earlier stage than unidirectional ones. This paper presents the results of an experiment comparing the degree of metaphor unidirectionality in two languages: Hebrew and Abui (spoken by some 16 000 people on the island of Alor in Indonesia). The results of the experiment show that metaphor unidirectionality is significantly higher in Hebrew than in Abui. Whereas Hebrew is a national language, Abui is a regional language of relatively low socio-political complexity. In accordance with the Evolutionary Inference Principle, the lower degree of metaphor unidirectionality of Abui may accordingly be reconstructed to an earlier stage in the evolution of language. The evolutionary journey from bidirectionality to unidirectionality in metaphors argued for here may be viewed as part of a larger package, whereby the development of grammatical complexity in various domains is driven by the incremental increases in socio-political complexity that characterize the course of human prehistory.

An early cell shape transition drives evolutionary expansion of the human forebrain
Silvia Benito-Kwiecinski et al.
Cell, forthcoming


The human brain has undergone rapid expansion since humans diverged from other great apes, but the mechanism of this human-specific enlargement is still unknown. Here, we use cerebral organoids derived from human, gorilla, and chimpanzee cells to study developmental mechanisms driving evolutionary brain expansion. We find that neuroepithelial differentiation is a protracted process in apes, involving a previously unrecognized transition state characterized by a change in cell shape. Furthermore, we show that human organoids are larger due to a delay in this transition, associated with differences in interkinetic nuclear migration and cell cycle length. Comparative RNA sequencing (RNA-seq) reveals differences in expression dynamics of cell morphogenesis factors, including ZEB2, a known epithelial-mesenchymal transition regulator. We show that ZEB2 promotes neuroepithelial transition, and its manipulation and downstream signaling leads to acquisition of nonhuman ape architecture in the human context and vice versa, establishing an important role for neuroepithelial cell shape in human brain expansion.

Extreme weather events and military conflict over seven centuries in ancient Korea
Tackseung Jun & Rajiv Sethi
Proceedings of the National Academy of Sciences, 23 March 2021


We explore the causal connection between weather and war by constructing and analyzing a dataset featuring extreme weather events and military conflicts involving a set of stable political entities that existed side by side over several centuries, namely, the three ancient kingdoms of the Korean Peninsula between 18 Before the Common Era and 660 Common Era. Conflicts are classified as desperate if a state experiencing the shock invades a neighbor and opportunistic if a state experiencing the shock is invaded by a neighbor. We find that weather-induced conflict was significant, but largely opportunistic rather than desperate. That is, states experiencing an adverse shock were more likely to be invaded, but not more likely to initiate attack. We also provide evidence that the channel through which weather shocks gave rise to opportunistic invasions was food insecurity, which weakened the power of states to repel attack. Since climate change is projected to give rise to an increased frequency of extreme weather events, these historical findings have contemporary relevance.

Where myth and archaeology meet: Discovering the Gorgon Medusa’s Lair
Clive Finlayson et al.
PLoS ONE, April 2021


Here we report the discovery of ceramic fragments that form part of a Gorgoneion, a ceramic image representation of the Gorgon Medusa. The fragments were found in a deep part of Gorham’s Cave, well known to ancient mariners as a natural shrine, between the 8th and 2nd century BCE. We discuss the context of this discovery, both within the inner topography of the cave itself, and also the broader geographical context. The discovery is situated at the extreme western end of the Mediterranean Sea, where it meets the Atlantic Ocean. The location was known to ancient mariners as the northern Pillar of Herakles, which marked the end of the known world. We relate the discovery, and its geographical and chronological context, to Greek legends that situated the lair of the Gorgon sisters at a location which coincides with the physical attributes and geographical position of Gorham’s Cave. We thus provide, uniquely, a geographical and archaeological context to the myth of Perseus and the slaying of the Gorgon Medusa.

Deep genetic affinity between coastal Pacific and Amazonian natives evidenced by Australasian ancestry
Marcos Araújo Castro e Silva et al.
Proceedings of the National Academy of Sciences, 6 April 2021


Different models have been proposed to elucidate the origins of the founding populations of America, along with the number of migratory waves and routes used by these first explorers. Settlements, both along the Pacific coast and on land, have been evidenced in genetic and archeological studies. However, the number of migratory waves and the origin of immigrants are still controversial topics. Here, we show the Australasian genetic signal is present in the Pacific coast region, indicating a more widespread signal distribution within South America and implicating an ancient contact between Pacific and Amazonian dwellers. We demonstrate that the Australasian population contribution was introduced in South America through the Pacific coastal route before the formation of the Amazonian branch, likely in the ancient coastal Pacific/Amazonian population. In addition, we detected a significant amount of interpopulation and intrapopulation variation in this genetic signal in South America. This study elucidates the genetic relationships of different ancestral components in the initial settlement of South America and proposes that the migratory route used by migrants who carried the Australasian ancestry led to the absence of this signal in the populations of Central and North America.

Innovative Homo sapiens behaviours 105,000 years ago in a wetter Kalahari
Jayne Wilkins et al.
Nature, forthcoming


The archaeological record of Africa provides the earliest evidence for the emergence of the complex symbolic and technological behaviours that characterize Homo sapiens. The coastal setting of many archaeological sites of the Late Pleistocene epoch, and the abundant shellfish remains recovered from them, has led to a dominant narrative in which modern human origins in southern Africa are intrinsically tied to the coast and marine resources, and behavioural innovations in the interior lag behind. However, stratified Late Pleistocene sites with good preservation and robust chronologies are rare in the interior of southern Africa, and the coastal hypothesis therefore remains untested. Here we show that early human innovations that are similar to those dated to around 105 thousand years ago (ka) in coastal southern Africa existed at around the same time among humans who lived over 600 km inland. We report evidence for the intentional collection of non-utilitarian objects (calcite crystals) and ostrich eggshell from excavations of a stratified rockshelter deposit in the southern Kalahari Basin, which we date by optically stimulated luminescence to around 105 ka. Uranium–thorium dating of relict tufa deposits indicates sporadic periods of substantial volumes of fresh, flowing water; the oldest of these episodes is dated to between 110 and 100 ka and is coeval with the archaeological deposit. Our results suggest that behavioural innovations among humans in the interior of southern Africa did not lag behind those of populations near the coast, and that these innovations may have developed within a wet savannah environment. Models that tie the emergence of behavioural innovations to the exploitation of coastal resources by our species may therefore require revision.

Ancient genomic time transect from the Central Asian Steppe unravels the history of the Scythians
Guido Alberto Gnecchi-Ruscone et al.
Science Advances, March 2021


The Scythians were a multitude of horse-warrior nomad cultures dwelling in the Eurasian steppe during the first millennium BCE. Because of the lack of first-hand written records, little is known about the origins and relations among the different cultures. To address these questions, we produced genome-wide data for 111 ancient individuals retrieved from 39 archaeological sites from the first millennia BCE and CE across the Central Asian Steppe. We uncovered major admixture events in the Late Bronze Age forming the genetic substratum for two main Iron Age gene-pools emerging around the Altai and the Urals respectively. Their demise was mirrored by new genetic turnovers, linked to the spread of the eastern nomad empires in the first centuries CE. Compared to the high genetic heterogeneity of the past, the homogenization of the present-day Kazakhs gene pool is notable, likely a result of 400 years of strict exogamous social rules.

Multiple migrations to the Philippines during the last 50,000 years
Maximilian Larena et al.
Proceedings of the National Academy of Sciences, 30 March 2021


Island Southeast Asia has recently produced several surprises regarding human history, but the region’s complex demography remains poorly understood. Here, we report ∼2.3 million genotypes from 1,028 individuals representing 115 indigenous Philippine populations and genome-sequence data from two ∼8,000-y-old individuals from Liangdao in the Taiwan Strait. We show that the Philippine islands were populated by at least five waves of human migration: initially by Northern and Southern Negritos (distantly related to Australian and Papuan groups), followed by Manobo, Sama, Papuan, and Cordilleran-related populations. The ancestors of Cordillerans diverged from indigenous peoples of Taiwan at least ∼8,000 y ago, prior to the arrival of paddy field rice agriculture in the Philippines ∼2,500 y ago, where some of their descendants remain to be the least admixed East Asian groups carrying an ancestry shared by all Austronesian-speaking populations. These observations contradict an exclusive “out-of-Taiwan” model of farming–language–people dispersal within the last four millennia for the Philippines and Island Southeast Asia. Sama-related ethnic groups of southwestern Philippines additionally experienced some minimal South Asian gene flow starting ∼1,000 y ago. Lastly, only a few lowlanders, accounting for <1% of all individuals, presented a low level of West Eurasian admixture, indicating a limited genetic legacy of Spanish colonization in the Philippines. Altogether, our findings reveal a multilayered history of the Philippines, which served as a crucial gateway for the movement of people that ultimately changed the genetic landscape of the Asia-Pacific region.


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