Urban evolution in the USA

On a sustained basis, cities are of non-uniform relative sizes.This paper addresses three basic issues which arise from thissimple observation by examining the size distribution of UScities over the period 1900–1990. First, we explore thereasons why there is a wide distribution of city sizes. Second,we characterize the evolution of the size distribution of cities,documenting growth in sizes and numbers of cities. We ask whetherthe relative size distribution of cities has remained stableover time, or if it has displayed, instead, a tendency to collapse,flatten, or otherwise change its shape. We also examine evidenceon whether the size distribution obeys Zipf's Law. Third, weexamine the degree and determinants of mobility of individualcities within this distribution, asking to what extent citiesare moving up and down in the distribution and how this movementis influenced by cities' geographic characteristics. We usea newly constructed data with consistent metropolitan area definitionsover this century, discussing the issues and linking our resultsto the relevant literature.     

Evidence of an Eleventh-Century AD Cola Nitida Trade into the Middle Niger Region

Kola nut (Cola cf. nitida) and Safou fruit (Dacryodes edulis) remains have been discovered in eleventh- to fourteenth-century archaeological contexts at Togu Missiri near Ségou in Mali. These remains are evidence of early trade in perishable foodstuffs from the West African forest zone into the Middle Niger region. On the basis of these finds, this paper argues that long-distance trade links were well established by the end of the first millennium AD. It thereby supports the hypothesis that dates the inception of trade between the West African forest zone and the savanna regions to the first millennium AD. The circumstances of the find are discussed, as are the implications for our understanding of the wider exchange network based on the Niger River system in the late first and early second millennium CE.

     

Archaeogenetic study of prehistoric rice remains from Thailand and India: evidence of early <Emphasis Type="Italic">japonica</Emphasis> in South and Southeast Asia

We report a successful extraction and sequencing of ancient DNA from carbonized rice grains (Oryza sativa) from six archaeological sites, including two from India and four from Thailand, ranging in age from ca. 2500 to 1500 BP. In total, 221 archaeological grains were processed by PCR amplification and primary-targeted fragments were sequenced for comparison with modern sequences generated from 112 modern rice populations, including crop and wild varieties. Our results include the genetic sequences from both the chloroplast and the nuclear genomes, based on four markers from the chloroplast and six from the nuclear genome. These markers allow differentiation of indica rice from japonica rice, the two major subspecies of Asian rice (O. sativa) considered to have separate geographical origins. One nuclear marker differentiates tropical and temperate forms of subspecies japonica. Other markers relate to phenotypic variation selected for under domestication, such as non-shattering, grain stickiness (waxy starch) and pericarp colour. Recovery and identification of sequences from nuclear markers was generally poor, whereas recovery of chloroplast sequences was successful, with at least one of four markers recovered in 61 % of archaeological grains. This allowed for successful differentiation of indica or japonica subspecies variety, with japonica identified in all the Thai material and a mixture of indica and japonica chloroplasts in the two Indian assemblages. Rice subspecies was also assessed through conventional archaeobotanical methods relying on grain metrics, based on measurements from 13 modern populations and 499 archaeological grains. Grain metrics also suggest a predominance of japonica-type grains in the Southeast Asian sites and a mixture of japonica and indica in the Indian sites with indica in the minority. The similar results of grain metrics and ancient DNA (aDNA) affirm that grain measurements have some degree of reliability in rice subspecies identification. The study also highlights the great potential of ancient DNA recovery from archaeological rice. The data generated in the present study adds support to the model of rice evolution that includes hybridization between japonica and proto-indica.