The 'human revolution' in lowland tropical Southeast Asia:the antiquity and behavior of anatomically modern humans at Niah Cave (Sarawak, Borneo)

Recent research in Europe, Africa, and Southeast Asia suggests that we can no longer assume a direct and exclusive link between anatomically modern humans and behavioral modernity (the 'human revolution'), and assume that the presence of either one implies the presence of the other: discussions of the emergence of cultural complexity have to proceed with greater scrutiny of the evidence on a site-by-site basis to establish secure associations between the archaeology present there and the hominins who created it. This paper presents one such case study: Niah Cave in Sarawak on the island of Borneo, famous for the discovery in 1958 in the West Mouth of the Great Cave of a modern human skull, the 'Deep Skull,' controversially associated with radiocarbon dates of ca. 40,000 years before the present. A new chronostratigraphy has been developed through a re-investigation of the lithostratigraphy left by the earlier excavations, AMS-dating using three different comparative pre-treatments including ABOX of charcoal, and U-series using the Diffusion-Absorption model applied to fragments of bones from the Deep Skull itself. Stratigraphic reasons for earlier uncertainties about the antiquity of the skull are examined, and it is shown not to be an `intrusive' artifact. It was probably excavated from fluvial-pond-desiccation deposits that accumulated episodically in a shallow basin immediately behind the cave entrance lip, in a climate that ranged from times of comparative aridity with complete desiccation, to episodes of greater surface wetness, changes attributed to regional climatic fluctuations. Vegetation outside the cave varied significantly over time, including wet lowland forest, montane forest, savannah, and grassland. The new dates and the lithostratigraphy relate the Deep Skull to evidence of episodes of human activity that range in date from ca. 46,000 to ca. 34,000 years ago. Initial investigations of sediment scorching, pollen, palynomorphs, phytoliths, plant macrofossils, and starch grains recovered from existing exposures, and of vertebrates from the current and the earlier excavations, suggest that human foraging during these times was marked by habitat-tailored hunting technologies, the collection and processing of toxic plants for consumption, and, perhaps, the use of fire at some forest-edges. The Niah evidence demonstrates the sophisticated nature of the subsistence behavior developed by modern humans to exploit the tropical environments that they encountered in Southeast Asia, including rainforest. (c) 2006 Elsevier Ltd. All rights reserved.

Levels of cadmium and zinc in soil and plants following the toxic spill from a pyrite mine, Aznalcollar, Spain

On 25 April 1998, a breach of the tailings dam of the Los Frailes pyrite mine in southwestern Spain resulted in the release of 6 million m(3) of acidic water and toxic sludge high in heavy metals. Contaminated material extended 40 km downstream, affecting agricultural land and parts of the wildlife-rich Donana Natural and National Parks, including the Entremuros, a very important area for birds. We report on the concentrations, distributions and bioavailability of zinc and cadmium in soil and vegetation from the Entremuros in November 1998 and October 1999, following 2 'cleanup' operations. Levels of Zn and Cd in soil increased significantly over this period, although this was not reflected consistently in metal concentrations in emergent macrophytes. We recommend monitoring of further cleanup attempts in order to develop means of minimizing potential impacts to wildlife in the area.

Arsenic uptake and metabolism in plants

Arsenic (As) is an element that is nonessential for and toxic to plants. Arsenic contamination in the environment occurs in many regions, and, depending on environmental factors, its accumulation in food crops may pose a health risk to humans.Recent progress in understanding the mechanisms of As uptake and metabolism in plants is reviewed here. Arsenate is taken up by phosphate transporters. A number of the aquaporin nodulin26-like intrinsic proteins (NIPs) are able to transport arsenite,the predominant form of As in reducing environments. In rice (Oryza sativa), arsenite uptake shares the highly efficient silicon (Si) pathway of entry to root cells and efflux towards the xylem. In root cells arsenate is rapidly reduced to arsenite, which is effluxed to the external medium, complexed by thiol peptides or translocated to shoots. One type of arsenate reductase has been identified, but its in planta functions remain to be investigated. Some fern species in the Pteridaceae family are able to hyperaccumulate As in above-ground tissues. Hyperaccumulation appears to involve enhanced arsenate uptake, decreased arsenite-thiol complexation and arsenite efflux to the external medium, greatly enhanced xylem translocation of arsenite, and vacuolar sequestration of arsenite in fronds. Current knowledge gaps and future research directions are also identified.

Toxic effects of cadmium and zinc on ectomycorrhizal colonization of scots pine (Pinus sylvestris L.) from soil inoculum

Scots pine seedlings colonized by ectomycorrhizal (ECM) fungi from natural soil inoculum were exposed to a range of Cd or Zn concentrations to investigate the effects of metals on ECM fungi-Scots pine associations in a realistic soil environment. Experiments focused on the relationship between the sensitivity of ECM fungi and their host plants, the influence of metals on ECM community dynamics on Scots pine roots, and the effects of metal exposure on ECM colonization from soil-borne propagules. Ectomycorrhizal colonization was inhibited by Cd and Zn, with a decrease in the proportion of ECM-colonized root tips. Shoot and root biomass, total root length, and total root-tip density, however, were unaffected by Cd or Zn. A decrease in the diversity of ECM morphotypes also occurred, which could have a negative effect on tree vigor. Overall, colonization by ECM fungi was more sensitive than seedling growth to Cd and Zn, and this could have serious implications for successful tree establishment on metal-contaminated soils.

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment?

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.