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R Potts

Publications and source records attributed to R Potts.

At least 19 recordsLinked to original sources
PubMed2001

Earliest presence of humans in northeast Asia.

The timing of the earliest habitation and oldest stone technologies in different regions of the world remains a contentious topic in the study of human evolution. Here we contribute to this debate with detailed magnetostratigraphic results on two exposed parallel sections of lacustrine sediments at Xiaochangliang in the Nihewan Basin, north China; these results place stringent controls on the age of Palaeolithic stone artifacts that were originally reported over two decades ago. Our palaeomagnetic findings indicate that the artifact layer resides in a reverse polarity magnetozone bounded by the Olduvai and Jaramillo subchrons. Coupled with an estimated rate of sedimentation, these findings constrain the layer's age to roughly 1.36 million years ago. This result represents the age of the oldest known stone assemblage comprising recognizable types of Palaeolithic tool in east Asia, and the earliest definite occupation in this region as far north as 40 degrees N.

Animals↗
PubMed2001

Effect of combination therapy on immunologic progression of human immunodeficiency virus at a population level.

There is accumulating evidence from clinical trials and cohort studies that highly active antiretroviral combination therapy is effective at halting immunologic and clinical progression of human immunodeficiency virus (HIV). Its impact at a population level is less well known because the regimes may be difficult to tolerate and compliance poorer. The authors make use of population data for almost all of the HIV-infected people in Scotland in 1997 who were under clinical care and monitor their response to therapy during the first year when these effective treatments became widely available. More than two thirds of the HIV-positive patients were on some form of antiretroviral therapy during the year. The authors show that all treated groups, even those who were on changing regimes, showed net improvement in immunologic status during the year. For the group of patients on triple or quadruple therapy, there was an average increase of more than 100 CD4 cells/mm(3) over the year, with other treatment groups showing more modest, but significant, increases.

Anti-HIV Agents↗
PubMed2000

Mid-Pleistocene Acheulean-like stone technology of the Bose basin, South China.

Stone artifacts from the Bose basin, South China, are associated with tektites dated to 803,000 +/- 3000 years ago and represent the oldest known large cutting tools (LCTs) in East Asia. Bose toolmaking is compatible with Mode 2 (Acheulean) technologies in Africa in its targeted manufacture and biased spatial distribution of LCTs, large-scale flaking, and high flake scar counts. Acheulean-like tools in the mid-Pleistocene of South China imply that Mode 2 technical advances were manifested in East Asia contemporaneously with handaxe technology in Africa and western Eurasia. Bose lithic technology is associated with a tektite airfall and forest burning.

Africa↗
PubMed2000

Outcomes templates.

Explore the source record for details and available documents.

Diabetes Mellitus, Type 2↗
PubMed1999

Current research on the late Pliocene and Pleistocene deposits north of Homa Mountain, southwestern Kenya.

The late Pliocene and Pleistocene sediments of the Homa Peninsula in southwestern Kenya are richly fossiliferous, preserve Early Stone Age archaeological traces and provide one of the few paleoanthropological data sets for the region between the branches of the East African Rift Valley. This paper presents preliminary results of our ongoing investigation of late Pliocene and Pleistocene deposits at the localities of Rawi, Kanam East, Kanam Central and Kanjera. While fossils have been collected from the peninsula since 1911, little systematic effort has been made to place them into a broader litho-and chronostratigraphic framework. This project has conclusively demonstrated that fossils occur in good stratigraphic context at all of the study localities and that claims of sediment slumping (Boswell, 1935) have been greatly overstated (Behrensmeyer et al., 1995; Plummer & Potts, 1989). A provisional chronostratigraphic framework based on magneto- and biostratigraphy is presented here. We have revised the Plio-Pleistocene stratigraphy of the Rawi and Kanam gullies to include three formations: the Rawi, Abundu and Kasibos Formations. Based on magneto- and biostratigraphy, these formations are dated between approximately three and one m.y.a. (Gauss Chron-Jaramillo Subchron) (Cande & Kent, 1995). The Apoko Formation unconformably overlies the others and may be middle to late Pleistocene in age. All formations contain rich patches of fossils, and Acheulean artifacts have been surface collected from the Abundu and Kasibos Formations. Deposition of the fossil- and artefact-bearing sediments at Kanjera North began in the early Pleistocene and continued into the middle Pleistocene. Deposition at Kanjera South began over one million years earlier than previously thought, at approximately 2.2 m.y.a., and continued into the Olduvai Subchron (1.770-1.950 m.y.a.; Cande & Kent, 1995). Excavations have recovered Oldowan artefacts in association with well-preserved fossil fauna near the base of the sequence, the oldest archaeological traces yet known from southwestern Kenya.

Animals↗
PubMed1999

Early pleistocene habitat in member 1 Olorgesailie based on paleosol stable isotopes.

Stable carbon and oxygen isotope values from soil carbonates were used to determine the vegetation context of archaeological sites and local climatic conditions represented in a approximately 0.99 Ma paleosol that is exposed laterally in the Olorgesailie basin, southern Kenya rift valley. As part of this landscape-scale project, samples of an upper Member 1 paleosol were analyzed along nearly 4 km of outcrop in three adjacent parts of the basin. Modern East African soil and plant community analogs are used to interpret the isotope ratios. The carbon isotopic composition of the paleosol carbonates indicates that the area supported a local biomass of about 75-100% C(4)plants during the period of soil formation. After averaging the data for each trench, an open C(4)grassland is represented by half of the carbon values, with wooded grassland more abundant across the paleolandscape than it is in the area now. This vegetational reconstruction is supported by the mammalian faunal assemblage, which has a high percentage of grazers. Although the relatively small sample size outside the main excavation area precludes firm characterization of vegetational diversity across the basin in upper Member 1 times, eastern and western localities in the study area may have had more woody C(3)plants than the widely sampled zone in between. Oxygen isotopes indicate that the lowland basin was slightly cooler and moister than today's semi-arid climate, with greater annual rainfall. Archaeological traces have a virtually continuous distribution across the paleolandscape, but vary in density of occurrence. With the strong evidence for C(4)grassland as the primary vegetation context across most of the study area, no habitat preference by the Acheulean toolmakers at Olorgesailie is shown in our initial comparison between carbon isotope values and stone/bone densities.

Animals↗
PubMed1999

Paleolandscape variation and early pleistocene hominid activities: members 1 and 7, Olorgesailie formation, Kenya.

Paleolandscape research tests for variation in the spatial distribution of hominid artefacts and establishes the association of hominid activities with paleoenvironmental features over distances of 100s to 1000s of meters. This approach requires (1) precise definition of narrow stratigraphic intervals based on sedimentary criteria that can be documented over a broad area, and (2) excavation of these intervals in order to establish taphonomic and paleoenvironmental contexts. In this report, excavations of three target intervals within the early Pleistocene deposits (992 to 780 ka) of the Olorgesailie basin are described. Assessment of time-averaging and paleolandscape structure shows that each target interval represents a relatively brief period (</=1000 yrs) and exhibits a unique distribution of environmental features (e.g., topographic gradients, channels, soil development). Stone artefacts and fossilized animal bones are distributed nonrandomly in each interval, and include clusters that were five to 293 times more densely concentrated than the laterally equivalent background scatter. A paleosol in upper Member 1 preserves a relatively continuous distribution of artefacts and fossils, in contrast with the more patchy distribution in two intervals of lower Member 7. We infer that the difference between the two members reflects a real variation in hominid land use-either a response to local environmental differences or perhaps a change through time in hominid interaction with the environment. By expanding the comparative analysis to diverse basins, it should be possible to test for broader evolutionary change in hominid activities. Examples drawn from East African Pliocene and early Pleistocene sites suggest that evolutionary change in land use entailed (1) wider ranging of hominids and longer distances of stone transport, (2) expansion of tool-assisted behaviors to a wider diversity of environmental settings, and (3) more strongly focused placement of particular artefact forms (e.g., bifaces) in different areas of the landscape in response to specific environmental features, such as lava outcrops, stream channels, and lake margins. ¿

Animals↗
PubMed1999

The impact of British and US guidelines for initiating combination antiretroviral therapy on estimating national treatment requirements for HIV-positive patients. Collaborating Immunologists and the Scottish HIV and AIDS Group.

This paper uses comprehensive national data on HIV positive patients in Scotland to carry out a needs assessment exercise for combination antiretroviral therapy. The objective of this study was to estimate the numbers of HIV positive patients in Scotland who would be eligible for combination antiretroviral therapy under current British and US guidelines and to demonstrate the impact of these different guidelines on the resources required. The proportion of the Scottish population that would be eligible for combination therapy ranged from 76% to 91%, under different guidelines for initiating therapy. We thus estimate that for countries such as Scotland, including western Europe and the United States, where a large proportion of the HIV population became infected in the early to mid-1980s, the majority of patients will be eligible for combination therapy, regardless of the guideline.

Adult↗
PubMed1998

Environmental hypotheses of hominin evolution.

The study of human evolution has long sought to explain major adaptations and trends that led to the origin of Homo sapiens. Environmental scenarios have played a pivotal role in this endeavor. They represent statements or, more commonly, assumptions concerning the adaptive context in which key hominin traits emerged. In many cases, however, these scenarios are based on very little if any data about the past settings in which early hominins lived. Several environmental hypotheses of human evolution are presented in this paper. Explicit test expectations are laid out, and a preliminary assessment of the hypotheses is made by examining the environmental records of Olduvai, Turkana, Olorgesailie, Zhoukoudian, Combe Grenal, and other hominin localities. Habitat-specific hypotheses have prevailed in almost all previous accounts of human adaptive history. The rise of African dry savanna is often cited as the critical event behind the development of terrestrial bipedality, stone toolmaking, and encephalized brains, among other traits. This savanna hypothesis has been countered recently by the woodland/forest hypothesis, which claims that Pliocene hominins had evolved in and were primarily attracted to closed habitats. The ideas that human evolution was fostered by cold habitats in higher latitudes or by seasonal variations in tropical and temperate zones also have their proponents. An alternative view, the variability selection hypothesis, states that large disparities in environmental conditions were responsible for important episodes of adaptive evolution. The resulting adaptations enhanced behavioral versatility and ultimately ecological diversity in the human lineage. Global environmental records for the late Cenozoic and specific records at hominin sites show the following: 1) early human habitats were subject to large-scale remodeling over time; 2) the evidence for environmental instability does not support habitat-specific explanations of key adaptive changes; 3) the range of environmental change over time was more extensive and the tempo far more prolonged than allowed by the seasonality hypothesis; and 4) the variability selection hypothesis is strongly supported by the persistence of hominins through long sequences of environmental remodeling and the origin of important adaptations in periods of wide habitat diversity. Early bipedality, stone transport, diversification of artifact contexts, encephalization, and enhanced cognitive and social functioning all may reflect adaptations to environmental novelty and highly varying selective contexts.

Adaptation, Physiological↗
PubMed1998

Effects of televised safety models on children's risk taking and hazard identification.

OBJECTIVE: To examine effects of televised safety models on children's willingness to take physical risks and their ability to identify injury hazards in common situations. METHODS: Sixty children, between the ages of five and eight years, were exposed to one of three TV stimulus programs: (1) a safety educational videotape, in which actors engaged in dangerous behavior, suffered injuries, and then enacted alternative safe behaviors; (2) an animated cartoon, which portrayed characters engaged in safety behaviors incidental to the main story line; or (3) the same cartoon program edited to omit the scenes depicting safety behavior. Children's willingness to take physical risks was measured before and after the TV stimulus by a series of pictorial child-relevant scenarios in which they could indicate the level of risk they would take. They also completed pretest and posttest measures of hazard identification, in which they were to identify injury hazards in several pictorial scenarios. RESULTS: Exposure to the safety educational videotape decreased children's willingness to take physical risks and increased their identification of injury hazards. Exposure to the animated cartoon with incidental safety components did not affect risk taking, but did increase ability to identify hazards. CONCLUSIONS: Findings are interpreted as evidence of observational learning and priming of thematically related knowledge by the television stimuli. Implications for safety educational curricula are discussed.

Analysis of Variance↗
PubMed1997

Late pliocene faunal turnover in the turkana basin, kenya and ethiopia

Analysis of a large sample of well-dated fossil mammals from localities in the Turkana Basin of Kenya and Ethiopia revealed sampling biases that affect patterns of faunal turnover during the late Pliocene. When these biases were accounted for, results indicated that 58 to 77 percent of the mammal species were replaced between 3.0 and 1.8 million years ago (Ma). Overall diversity increased from 3.0 to 2.0 Ma but then declined. No distinct turnover pulse is seen between 2.8 and 2.5 Ma; instead, the most significant period of faunal change began after 2.5 Ma and continued through 1.8 Ma.

Journal Article↗
PubMed1997

Brief report: cross-validation of the Injury Behavior Checklist in a school-age sample.

Examined descriptive characteristics, internal validity, and convergent validity of the Injury Behavior Checklist (IBC) in a sample of 7- to 10-year-old children. Although the IBC was originally designed for use with preschool children, results of the present study showed that it has acceptable psychometric qualities for use with children as old as 9 years. The IBC shows promise as an easily administered instrument for research on psychological and behavioral mechanisms of childhood injury, as well as for individual screening for injury liability.

Child↗
PubMed1997

A theoretical study of outermost skin layer electroporation.

Two models of electrohydration of stratum corneum (SC) have been developed. In the first model, the hydration of one interbilayer region is considered on the assumption that water molecules are adsorbed on the inhomogeneous surface of a bilayer and can interact, thereby lowering their energy on the surface. The dependence of the hydration degree on the voltage across the skin had been found. At certain parameter values the degree of hydration rapidly grows at certain voltage up to the magnitudes at which continuous water pathways appear. The second model has used the macroscopic approach which presumes water to be present in the interbilayer region as microdrops. The dependence of the hydration degree on voltage has been also found. At voltages of the order of tens of volts the obtained hydrations of interbilayer regions are sufficient to generate electroinduced hydrophilic pores in the SC lipid phase. Formation of tortuous continuous pathways for the transport of small ions is little probable because it requires voltages much higher than 100 V. We suggest that small ions pass the skin by the straight way through corneocytes and lipid bilayers at voltages of the order of tens of volts and higher.

Electroporation↗
PubMed1996

A content analysis of safety behaviors of television characters: implications for children's safety and injury.

Examined frequency and characteristics of safety behaviors in television programs popular with child audiences. A sample of 52 programs was coded for safety event location, demographic characteristics of safety models, social and physical contexts of safety events, and successful or unsuccessful outcomes of safety behaviors. Results indicate an overall rate of 13 safety behaviors per hour, with hour half of all safety behaviors located in commercial advertisements. Most safety behaviors were performed by made adult characters, had limited relevance for children, and were not associated with either positive or negative outcomes. Findings are discussed in terms of their relevance for observational learning of safety behaviors by child viewers.

Adolescent↗
PubMed1995

Hominid fossil sample from Kanjera, Kenya: description, provenance, and implications of new and earlier discoveries.

Anatomically modern hominids were first collected from Kanjera, Kenya, by L.S.B. Leakey in the 1930s. Their apparent association with an archaic fauna was quickly challenged, throwing their age into doubt. Further unpublished hominid fragments were collected in 1974, 1975, 1981, and 1987. We review the context and morphology of the entire hominid sample. A minimum number of five individuals is represented by both cranial and postcranial elements. Several individuals have thickened cranial vaults, a characteristic originally thought to reflect their great antiquity. Vault thickening resulted from diploic expansion and may have been a response to acquired or inherited anemia. The entire hominid sample postdates the Kanjera Formation, deposited from the early into the middle Pleistocene. Most of the sample was derived from the black cotton soil capping the stratigraphic column. The morphology and context of the Kanjera hominids is consistent with human skeletal remains from nearby Holocene sites. Hominid 3 was probably an intrusive burial into an early Pleistocene bed.

Animals↗
PubMed1995

Childhood risk taking and injury: self-report and informant measures.

Examined several measures of children's physical risk taking and sensation seeking. These variables were targeted as potential predictors of unintentional injury, which is the leading cause of death in children. 83 children between 6 and 9 years of age completed self-report risk-taking and sensation-seeking scales, and a peer nomination measure of each classmate's risk taking. Teachers rated children on a risk-taking scale. Parents completed the Injury Behavior Checklist of risky behaviors, and also indicated their child's injury history. Virtually all measures were positively and significantly intercorrelated, indicating that reports of children's physical risk-taking behavior were consistent and were indicative of parent-reported injury frequency.

Accidents↗
PubMed1994

Effects of television content on physical risk-taking in children.

This study is an investigation of effects of risk-taking by characters in television programs on children's self-reported willingness to take physical risks. Twenty-four boys and 26 girls, ages 6 to 9 years, were assigned to view TV stimulus programs with infrequent physical risk-taking. TV stimulus programs with frequent risk-taking, or no TV stimuli. A self-report measure was used to assess children's willingness to take physical risks in several common injury-relevant situations. Five of the items were administered as a pretest before children watched the stimulus programs and five items were used as a post-test after they viewed the programs. A validation assessment on an independent sample of children indicated that the risk-taking measure was positively correlated with other measures of risk-taking as well as physical injuries. Results indicated that children who viewed the high-risk TV programs increased their self-reported risk-taking significantly more than children in the low-risk TV and no-TV control conditions. Findings are discussed within a theoretical context of observational learning processes, with implications for childhood injury.

Analysis of Variance↗