Ancient genomes reveal millet farming-related demic diffusion from the Yellow River into southwest China.

The study of southwest China is vital for understanding the dispersal and development of farming because of the coexistence of millet and rice in this region since the Neolithic period.1,2 However, the process of the Neolithic transition in southwest China is largely unknown, mainly due to the lack of ancient DNA from the Neolithic period. Here, we report genome-wide data from 11 human samples from the Gaoshan and Haimenkou sites with mixed farming of millet and rice dating to between 4,500 and 3,000 years before present in southwest China. The two ancient groups derived approximately 90% of their ancestry from the Neolithic Yellow River farmers, suggesting a demic diffusion of millet farming to southwest China. We inferred their remaining ancestry to be derived from a Hòabìnhian-related hunter-gatherer lineage. We did not detect rice farmer-related ancestry in the two ancient groups, which indicates that they likely adopted rice farming without genetic assimilation. We, however, observed rice farmer-related ancestry in the formation of some present-day Tibeto-Burman populations. Our results suggested the occurrence of both demic and cultural diffusion in the development of Neolithic mixed farming in some parts of southwest China.

Reassessing the role of climate change in the Tupi expansion (South America, 5000-500 BP).

The expansion of forest farmers across tropical lowland South America during the Late Holocene has long been connected to climate change. The more humid conditions established during the Late Holocene are assumed to have driven the expansion of forests, which would have facilitated the dispersal of cultures that practised agroforestry. The Tupi, a language family of widespread distribution in South America, occupies a central place in the debate. Not only are they one of the largest families in the continent, but their expansion from an Amazonian homeland has long been hypothesized to have followed forested environments wherever they settled. Here, we assess that hypothesis using a simulation approach. We employ equation-based and cellular automaton models, simulating demic-diffusion processes under two different scenarios: a null model in which all land cells can be equally settled, and an alternative model in which non-forested cells cannot be settled or delay the expansion. We show that including land cover as a constraint to movement results in a better approximation of the Tupi expansion as reconstructed by archaeology and linguistics.

Estimating the relative importance of demic and cultural diffusion in the spread of the Neolithic in Scandinavia.

Using a database of early farming sites in Scandinavia, we estimate that the spread rate of the Neolithic was in the range 0.44-0.66 km yr-1 This is substantially slower (by about 50%) than the rate in continental Europe. We interpret this result in the framework of a new mathematical model that includes horizontal cultural transmission (acculturation), vertical cultural transmission (interbreeding) and demic diffusion (reproduction and dispersal of farmers). To parametrize the model, we estimate reproduction rates of early farmers using archaeological data (sum-calibrated probabilities for the dates of early Neolithic Scandinavian sites) and use them in a wave-of-advance model for the first time. Comparing the model with the archaeological data, we find that the percentage of the spread rate due to cultural diffusion is below 50% (except for very extreme parameter values, and even for them it is below 54%). This strongly suggests that the spread of the Neolithic in Scandinavia was driven mainly by demic diffusion. This conclusion, obtained from archaeological data, agrees qualitatively with the implications of ancient genetic data, but the latter are yet too few in Scandinavia to produce any quantitative percentage for the spread rate due to cultural diffusion. We also find that, on average, fewer than eight hunter-gatherers were incorporated in the Neolithic communities by each group of 10 pioneering farmers, via horizontal and/or vertical cultural transmission.

Inferring patterns of folktale diffusion using genomic data.

Observable patterns of cultural variation are consistently intertwined with demic movements, cultural diffusion, and adaptation to different ecological contexts [Cavalli-Sforza and Feldman (1981) Cultural Transmission and Evolution: A Quantitative Approach; Boyd and Richerson (1985) Culture and the Evolutionary Process]. The quantitative study of gene-culture coevolution has focused in particular on the mechanisms responsible for change in frequency and attributes of cultural traits, the spread of cultural information through demic and cultural diffusion, and detecting relationships between genetic and cultural lineages. Here, we make use of worldwide whole-genome sequences [Pagani et al. (2016) Nature 538:238-242] to assess the impact of processes involving population movement and replacement on cultural diversity, focusing on the variability observed in folktale traditions (n = 596) [Uther (2004) The Types of International Folktales: A Classification and Bibliography. Based on the System of Antti Aarne and Stith Thompson] in Eurasia. We find that a model of cultural diffusion predicted by isolation-by-distance alone is not sufficient to explain the observed patterns, especially at small spatial scales (up to [Formula: see text]4,000 km). We also provide an empirical approach to infer presence and impact of ethnolinguistic barriers preventing the unbiased transmission of both genetic and cultural information. After correcting for the effect of ethnolinguistic boundaries, we show that, of the alternative models that we propose, the one entailing cultural diffusion biased by linguistic differences is the most plausible. Additionally, we identify 15 tales that are more likely to be predominantly transmitted through population movement and replacement and locate putative focal areas for a set of tales that are spread worldwide.

Modeling Demic and Cultural Diffusion: An Introduction.

Identifying the processes by which human cultures spread across different populations is one of the most topical objectives shared among different fields of study. Seminal works have analyzed a variety of data and attempted to determine whether empirically observed patterns are the result of demic and/or cultural diffusion. This special issue collects articles exploring several themes (from modes of cultural transmission to drivers of dispersal mechanisms) and contexts (from the Neolithic in Europe to the spread of computer programming languages), which offer new insights that will augment the theoretical and empirical basis for the study of demic and cultural diffusion. In this introduction we outline the state of art in the modeling of these processes, briefly discuss the pros and cons of two of the most commonly used frameworks (equation-based models and agent-based models), and summarize the significance of each article in this special issue.

Demographic transitions and migration in prehistoric East/Southeast Asia through the lens of nonmetric dental traits.

The aim of this study is to examine and assess the nonmetric dental trait evidence for the population history of East and Southeast Asia and, more specifically, to test the two-layer hypothesis for the peopling of Southeast Asia. Using a battery of 21 nonmetric dental traits we examine 7,247 individuals representing 58 samples drawn from East and Southeast Asian populations inhabiting the region from the late Pleistocene, through the Neolithic, Bronze Age, Iron Age, and into the historic and modern periods. The chief data reduction technique is a neighbor-joining tree generated from the triangular matrix of mean measure of divergence values. Principal findings indicated a major dichotomization of the dataset into (1) an early Southeast Asian sample with close affinities to modern Australian and Melanesian populations and (2) a very distinct grouping of ancient and modern Northeast Asians. Distinct patterns of clinal variation among Neolithic and post-Neolithic Mainland Southeast Asian samples suggest a center to periphery spread of genes into the region from Northeast Asia. This pattern is consistent with archaeological and linguistic evidence for demic diffusion that accompanied agriculturally driven population expansion in the Neolithic. Later Metal Age affinities between Island and Mainland coastal populations with Northeast Asian series is likely a consequence of a South China Sea interaction sphere operating from at least 500 BCE, if not from the Neolithic. Such results provide extensive support for the two-layer hypothesis to account for the population history of the region.

EVOLUTION AND POPULATION STRUCTURE OF AFRICANIZED HONEY BEES IN BRAZIL: EVIDENCE FROM SPATIAL ANALYSIS OF MORPHOMETRIC DATA.

In recent years, studies based on isoenzymatic patterns of geographic variation have revealed that what is usually called the Africanized honey bee does not constitute a single population. Instead, several local populations exist with various degrees of admixture with European honey bees. In this paper, we evaluated new data on morphometric patterns of Africanized honey bees collected at 42 localities in Brazil, using univariate and multivariate (canonical) trend surface and spatial autocorrelation analyses. The clinal patterns of variation found for genetically independent characters (wing size characters and some wing venation angles) are concordant with previous studies of malate dehydrogenase (MDH) allelic frequencies and support the hypothesis that larger honey bees in southern and southeastern Brazil originated by racial admixture in the initial phases of African honey bee colonization. Geographic variation patterns of Africanized honey bee populations reflect a demic diffusion process in which European genes were gradually lost because of the higher fitness of the African gene pool in Neotropical environmental conditions.