Do chimpanzees (Pan troglodytes) and 2-year-old children (Homo sapiens) understand double invisible displacement?

Chimpanzees (Pan troglodytes) and young children (Homo sapiens) have difficulty with double invisible displacements in which an object is hidden in two nonadjacent boxes in a linear array. Experiment 1 eliminated the possibility that chimpanzees' previous poor performance was due to the hiding direction of the displacement device. As in Call (2001), subjects failed double nonadjacent displacements, showing a tendency to select adjacent boxes. In Experiments 2 and 3, chimpanzees and 24-month-old children were tested on a new adaptation of the task in which four hiding boxes were presented in a diamond-shaped array on a vertical plane. Both species performed above chance on double invisible displacements using this format, suggesting that previous poor performance was due to a response bias or inhibition problem rather than a fundamental limitation in representational capacity.

Controlling leucine zipper specificity with interfacial hydrophobic residues

Dimerisation of leucine zippers results from the parallel association of alpha-helices to form a coiled coil. Coiled coils comprise a heptad repeat, denoted as (abcdefg)(n), where residues at positions a and d are hydrophobic and constitute the core of the dimer interface. Charged amino acids at the e and g positions of the coiled coil are thought to be the major influence on dimerisation specificity through the formation of attractive and repulsive interhelical electrostatic interactions. However, the variability of a-position residues in leucine zipper transcription factors prompted us to investigate their influence on dimerisation specificity. We demonstrate that mutation of a single interfacial a-position Ala residue to either Val, Ile or Leu significantly alters the homo- and heterodimerisation specificities of the leucine zipper domain from the c-Jun transcription factor. These results illustrate the importance of a-position residues in controlling leucine zipper dimerisation specificity in addition to providing substantial contributions to dimer stability.

Homomeric ring assemblies of eukaryotic Sm proteins have affinity for both RNA and DNA - Crystal structure of an oligomeric complex of yeast SmF

Sm and Sm-like proteins are key components of small ribonucleoproteins involved in many RNA and DNA processing pathways. In eukaryotes, these complexes contain seven unique Sm or Sm-like (Lsm) proteins assembled as hetero-heptameric rings, whereas in Archaea and bacteria six or seven-membered rings are made from only a single polypeptide chain. Here we show that single Sm and Lsm proteins from yeast also have the capacity to assemble into homo-oligomeric rings. Formation of homo-oligomers by the spliceosomal small nuclear ribonucleoprotein components SmE and SmF preclude hetero-interactions vital to formation of functional small nuclear RNP complexes in vivo. To better understand these unusual complexes, we have determined the crystal structure of the homomeric assembly of the spliceosomal protein SmF. Like its archaeal/bacterial homologs, the SmF complex forms a homomeric ring but in an entirely novel arrangement whereby two heptameric rings form a co-axially stacked dimer via interactions mediated by the variable loops of the individual SmF protein chains. Furthermore, we demonstrate that the homomeric assemblies of yeast Sm and Lsm proteins are capable of binding not only to oligo(U) RNA but, in the case of SmF, also to oligo(dT) single-stranded DNA.

Thermal ionization mass spectrometry U-series dating of a hominid site near Nanjing, China

Mass spectrometric U-series dating of speleothems from Tangshan Cave, combined with ecological and paleoclimatic evidence, indicates that Nanjing Man, a typical Homo erectus morphologically correlated with Peking Man at Zhoukoudian, should be at least 580 k.y. old, or more likely lived during the glacial oxygen isotope stage 16 (similar to 620 ka). Such an age estimate, which is similar to 270 ka older than previous electron spin resonance and alpha counting U-series dates, has significant implications for the evolution of Asian H. erectus. Dentine and enamel samples from the coexisting fossil layer yield significantly younger apparent ages, that of the enamel sample being only less than one-fourth of the minimum age of Nanjing Man. This suggests that U uptake history is far more complex than existing models can handle. As a result, great care must be taken in the interpretation of electron spin resonance and U-series dates of fossil teeth.

U-Series dating of Liujiang hominid site in Guangxi, Southern China

It has been established that modern humans were living in the Levant and Africa ca. 100 ka ago. Hitherto, this has contrasted with the situation in China where no unequivocal specimens of this species have been securely dated to more than 30 ka. Here we present the results of stratigraphic studies and U-series dating of the Tongtianyan Cave, the discovery site of the Liujiang hominid, which represents one of the few well-preserved fossils of modern Homo sapiens in China. The human fossils are inferred to come from either a refilling breccia or a primarily deposited gravel-bearing sandy clay layer. In the former case, which is better supported, the fossils would date to at least similar to 68 ka, but more likely to similar to 111-139 ka. Alternatively, they would be older than, similar to 153 ka. Both scenarios would make the Liujiang hominid one of the earliest modem humans in East Asia, possibly contemporaneous with the earliest known representatives from the Levant and Africa. Parallel studies on other Chinese localities have provided supporting evidence for the redating of Liujiang, which may have important implications for, the origin of modem humans. (C) 2002 Elsevier Science Ltd. All rights reserved.

Comparative study of Li, Na, and K adsorptions on graphite by using ab initio method

A comprehensive study has been conducted to compare the adsorptions of alkali metals (including Li, Na, and K) on the basal plane of graphite by using molecular orbital theory calculations. All three metal atoms prefer to be adsorbed on the middle hollow site above a hexagonal aromatic ring. A novel phenomenon was observed, that is, Na, instead of Li or K, is the weakest among the three types of metal atoms in adsorption. The reason is that the SOMO (single occupied molecular orbital) of the Na atom is exactly at the middle point between the HOMO and the LUMO of the graphite layer in energy level. As a result, the SOMO of Na cannot form a stable interaction with either the HOMO or the LUMO of the graphite. On the other hand, the SOMO of Li and K can form a relatively stable interaction with either the HOMO or the LUMO of graphite. Why Li has a relatively stronger adsorption than K on graphite has also been interpreted on the basis of their molecular-orbital energy levels.

Archaeology and age of a new hominin from Flores in eastern Indonesia

Excavations at Liang Bua, a large limestone cave on the island of Flores in eastern Indonesia, have yielded evidence for a population of tiny hominins, sufficiently distinct anatomically to be assigned to a new species, Homo floresiensis(1). The finds comprise the cranial and some post-cranial remains of one individual, as well as a premolar from another individual in older deposits. Here we describe their context, implications and the remaining archaeological uncertainties. Dating by radiocarbon (C-14), luminescence, uranium-series and electron spin resonance (ESR) methods indicates that H. floresiensis existed from before 38,000 years ago (kyr) until at least 18 kyr. Associated deposits contain stone artefacts and animal remains, including Komodo dragon and an endemic, dwarfed species of Stegodon. H. floresiensis originated from an early dispersal of Homo erectus ( including specimens referred to as Homo ergaster and Homo georgicus)(1) that reached Flores, and then survived on this island refuge until relatively recently. It overlapped significantly in time with Homo sapiens in the region(2,3), but we do not know if or how the two species interacted.

U-series dating of Locality 15 at Zhoukoudian, China, and implications for hominid evolution

This paper reports U-series dates on speleothem samples from Locality 15 at Zhoukoudian, one of the richest Paleolithic sites in northern China. The age of the lower part of Layer 2 is securely bracketed between 155,000 and 284,000 yr. The underlying Layer 3 dates back at least 284,000 yr. Layer 4, further below, should be older still, possibly by a cycle on the SPECMAP time scale before 284,000 yr ago. These ages, much greater than the previous estimates of 110,000-140,000 yr from U-series and electron spin resonance dating of fossil teeth, suggest that Locality 15 was broadly contemporaneous with Locality 4 (New Cave) and with the uppermost strata of Locality 1 (Peking Man site). The physical evolution and cultural development evidenced by the timing of the Zhoukoudian localities are in line with the opinion of Chinese anthropologists for a regional transition from Homo erectus to archaic Homo sapiens. (C) 2004 University of Washington. All rights reserved.

How primatology can inform us about the evolution of the humand mind

Humans are primates. We have evolved from common ancestors and the evolution of the human body is becoming increasingly clear as the archeological record expands. But for most people the gap between humans and animals lies in the mind, not in the body. And minds do not fossilise. To reconstruct the evolution of mind, scholars have thus increasingly looked to our closest relatives for clues. Here I discuss four ways in which the study of primates may inform such reconstruction: fact-finding, phylogenetic reconstruction, analogy, and regression models. Knowledge about primates can help us bridge the gap. Extinction of our closest relatives, on the other hand, would not only deplete that source of information but also increase the apparent differences between animal and human minds. It is likely that we have a long history of displacing closely related species, including the other hominids, leading us to appear ever more unique.