Long past

Kevin Lewis

October 21, 2018

Progressive aridification in East Africa over the last half million years and implications for human evolution
Bernhart Owen et al.
Proceedings of the National Academy of Sciences, forthcoming


Evidence for Quaternary climate change in East Africa has been derived from outcrops on land and lake cores and from marine dust, leaf wax, and pollen records. These data have previously been used to evaluate the impact of climate change on hominin evolution, but correlations have proved to be difficult, given poor data continuity and the great distances between marine cores and terrestrial basins where fossil evidence is located. Here, we present continental coring evidence for progressive aridification since about 575 thousand years before present (ka), based on Lake Magadi (Kenya) sediments. This long-term drying trend was interrupted by many wet–dry cycles, with the greatest variability developing during times of high eccentricity-modulated precession. Intense aridification apparent in the Magadi record took place between 525 and 400 ka, with relatively persistent arid conditions after 350 ka and through to the present. Arid conditions in the Magadi Basin coincide with the Mid-Brunhes Event and overlap with mammalian extinctions in the South Kenya Rift between 500 and 400 ka. The 525 to 400 ka arid phase developed in the South Kenya Rift between the period when the last Acheulean tools are reported (at about 500 ka) and before the appearance of Middle Stone Age artifacts (by about 320 ka). Our data suggest that increasing Middle- to Late-Pleistocene aridification and environmental variability may have been drivers in the physical and cultural evolution of Homo sapiens in East Africa.

Ritual responses to drought: An examination of ritual expressions in Classic Maya written sources
Eva Jobbová, Christophe Helmke & Andrew Bevan
Human Ecology, October 2018, Pages 759–781


Planting and rain-beckoning rituals are an extremely common way in which past and present human communities have confronted the risk of drought across a range of environments worldwide. In tropical environments, such ceremonies are particularly salient despite widespread assumptions that water supplies are unproblematic in such regions. We demonstrate for the first time that two common but previously under-appreciated Maya rituals are likely planting and rain-beckoning rituals preferentially performed at certain times of the year in close step with the rainy season and the Maya agricultural cycle. We also argue for considerable historical continuity between these Classic Maya ceremonies and later Maya community rituals still performed in times of uncertain weather conditions up to the present day across Guatemala, Belize, and eastern Mexico. During the Terminal Classic period (AD 800-900), the changing role played by ancient Maya drought-related rituals fits into a wider rhetorical shift observed in Maya texts away from the more characteristic focus on royal births, enthronements, marriages, and wars towards greater emphasis on the correct perpetuation of key ceremonies, and we argue that such changes are consistent with palaeoclimatic evidence for a period of diminished precipitation and recurrent drought.

Towards an explanation of inequality in premodern societies: The role of colonies, urbanization, and high population density
Branko Milanovic
Economic History Review, November 2018, Pages 1029-1047


Using a newly expanded set of 41 social tables from premodern societies, this article tries to identify the factors associated with the level of inequality and the inequality extraction ratio (how close to the maximum inequality the elites have pushed actual inequality). Strong evidence is found to show that elites in colonies were more extractive, and that more densely populated and less urbanized countries exhibited lower extraction ratios. Several possibilities are proposed, linking high population density to low inequality and to low elite extraction.

Enhanced Cognitive Flexibility in the Seminomadic Himba
Sarah Pope et al.
Journal of Cross-Cultural Psychology, forthcoming


Through codified rule-use, humans can accurately solve many problems. Yet, mechanized strategies can also be costly. After adopting a solution strategy, humans often become blind to alternatives, even when those alternatives are more efficient. Termed cognitive set, this failure to switch from a familiar strategy to a better alternative has been considered universally human. Yet, our understanding of this phenomenon is derived almost exclusively from Western subjects. In this study, we used the nonverbal Learned Strategy–Direct Strategy (LS-DS) touchscreen task in which subjects are presented with an opportunity to use either a learned strategy or a more efficient, but novel, shortcut. We found that the remote, seminomadic Himba of northern Namibia exhibited enhanced shortcut-use on the LS-DS task, challenging the claim that cognitive set affects humans universally. In addition, we found that altering subjects’ conceptualization of the shortcut as a viable option significantly enhanced its subsequent use in Western but not Himba participants. We discuss how other aspects of cultural variation, namely, environmental uncertainty and educational background, might contribute to the observed cross-cultural differences in flexible strategy-use.

Word Forms Are Structured for Efficient Use
Kyle Mahowald et al.
Cognitive Science, forthcoming


Zipf famously stated that, if natural language lexicons are structured for efficient communication, the words that are used the most frequently should require the least effort. This observation explains the famous finding that the most frequent words in a language tend to be short. A related prediction is that, even within words of the same length, the most frequent word forms should be the ones that are easiest to produce and understand. Using orthographics as a proxy for phonetics, we test this hypothesis using corpora of 96 languages from Wikipedia. We find that, across a variety of languages and language families and controlling for length, the most frequent forms in a language tend to be more orthographically well‐formed and have more orthographic neighbors than less frequent forms. We interpret this result as evidence that lexicons are structured by language usage pressures to facilitate efficient communication.

The neolithic revolution and contemporary sex ratios
Per Fredriksson & Satyendra Kumar Gupta
Economics Letters, forthcoming


This study establishes a positive and robust association between the present-day country-level male-to-female sex ratio (at birth, 0–4, 0–14 year olds) and the pre-colonial experience with sedentary agricultural activities (the Neolithic Revolution). In comparison, historical plough use has a less robust impact on the sex ratio at birth, but a positive association for the 0–4 and 0–14 age groups.


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