Categories and gatherings: Group selection and the mythology of cultural anthropology

If the term “group selection” is to have any meaning beyond mere semantics, it must refer to situations where individuals live in groups. Although the terminology of cultural anthropology suggests that humans live in bounded and enduring gatherings that might serve as group “vehicles” of selection, we argue that none of the terms asserted to be such an entity (i.e., clans, lineages, villages, bands, tribes, populations, societies, and cultures) fulfill this requirement. This is because these terms refer to: (1) reified abstractions, (2) groups only in the sense of categories of people instead of groups in the sense of people gathered together, or (3) gatherings that are much too fluid and fuzzy in their membership to be “vehicles.” Following Murdock (1972), we refer to this obsession with groups as “anthropology's mythology,” and we suggest that it is the result of our evolved capacity for categorical perception. Although classifying phenomena into categories is useful in many situations, it has hindered our understanding of human social organization and human evolution.     

Direct Cloning of Human 10q25 Neocentromere DNA Using Transformation-Associated Recombination (TAR) in Yeast

The transformation-associated recombination (TAR) procedure allows rapid, site-directed cloning of specific human chromosomal regions as yeast artificial chromosomes (YACs). The procedure requires knowledge of only a single, relatively small genomic sequence that resides adjacent to the chromosomal region of interest. We applied this approach to the cloning of the neocentromere DNA of a marker chromosome that we have previously shown to have originated through the activation of a latent centromere at human chromosome 10q25. Using a unique 1.4-kb DNA fragment as a “hook” in TAR experiments, we achieved single-step isolation of the critical neocentromere DNA region as two stable, 110- and 80-kb circular YACs. For obtaining large quantities of highly purified DNA, these YACs were retrofitted with the yeast–bacteria–mammalian-cells shuttle vector BRV1, electroporated intoEscherichia coliDH10B, and isolated as bacterial artificial chromosomes (BACs). Extensive characterization of these YACs and BACs by PCR and restriction analyses revealed that they are identical to the corresponding regions of the normal chromosome 10 and provided further support for the formation of the neocentromere within the marker chromosome through epigenetic activation.     

Performance Characterization of Watson Ahumada Motion Detector Using Random Dot Rotary Motion Stimuli

The performance of Watson & Ahumada''s model of human visual motion sensing is compared against human psychophysical performance. The stimulus consists of random dots undergoing rotary motion, displayed in a circular annulus. The model matches psychophysical observer performance with respect to most parameters. It is able to replicate some key psychophysical findings such as invariance of observer performance to dot density in the display, and decrease of observer performance with frame duration of the display.Associated with the concept of rotary motion is the notion of a center about which rotation occurs. One might think that for accurate estimation of rotary motion in the display, this center must be accurately known. A simple vector analysis reveals that this need not be the case. Numerical simulations confirm this result, and may explain the position invariance of MST(d) cells. Position invariance is the experimental finding that rotary motion sensitive cells are insensitive to where in their receptive field rotation occurs.When all the dots in the display are randomly drawn from a uniform distribution, illusory rotary motion is perceived. This case was investigated by Rose & Blake previously, who termed the illusory rotary motion the omega effect. Two important experimental findings are reported concerning this effect. First, although the display of random dots evokes perception of rotary motion, the direction of motion perceived does not depend on what dot pattern is shown. Second, the time interval between spontaneous flips in perceived direction is lognormally distributed (mode≈2 s). These findings suggest the omega effect fits in the category of a typical bistable illusion, and therefore the processes that give rise to this illusion may be the same processes that underlie much of other bistable phenomenon.     

Behavioral and environmental events influencing primate testosterone levels

A series of experiments demonstrated the influence of multiple environmental and social variables upon circulating testosterone levels in the rhesus monkey. Independent and interaction effects were revealed and a complex model was required to relate the action of these variables to particular measured levels of hormone. The generality of this model is being tested by comparisons with available human data and by extension of the studies to several additional Old World monkeys.Initial experiments included regularly scheduled sampling from 41 adult and eight juvenile rhesus monkey males. The subjects were maintained in stable or manipulated social groups and studied longitudinally with samples obtained before, during and after each experimental manipulation. The following factors were shown to influence levels of circulating testosterone: (1) ontogenetic status, (2) circadian rhythms, (3) relative access to females, (4) season (seasonal mating typical of rhesus), (5) alterations in social rank and (6) “successful” and “unsuccessful” agonistic encounters.Attempts to clarify the relationship between behavior and hormones must account for these (and perhaps other) stimulus variables. Although such a model may be highly complex, it does permit some predictive success and appears compatible with available human data. Further comparative studies will indicate the extent to which this model may be extrapolated to humans.     

Endocranial volumes of early African hominids, and the role of the brain in human mosaic evolution

Volumetric data are presented for 16 of the early hominids from both South and East Africa. Although the sample sizes are small, the statistical data support the conclusion that at least three taxa are represented; Australopithecus africanus, A. robustus, and Homo habilis. These data, plus certain morphological attributes, indicate that the brains of early hominids were reorganized to a human pattern, regardless of their small endocranial capacities. Some speculative suggestions are made regarding the possible relationship between brain and body weights, as well as Stephan's (1972) “progression indices”. If the speculations are correct, they provide additional support for the idea that brain reorganization occurred early in human evolution, and that concepts which regard the brain as having a more terminal role in human mosaic evolution are incorrect, as all of the fossil encephalization or “progression indices” are in the range of modern Homo sapiens.     

Testing the Generality of a Trophic-cascade Model for Plague

Climate may affect the dynamics of infectious diseases by shifting pathogen, vector, or host species abundance, population dynamics, or community interactions. Black-tailed prairie dogs (Cynomys ludovicianus) are highly susceptible to plague, yet little is known about factors that influence the dynamics of plague epizootics in prairie dogs. We investigated temporal patterns of plague occurrence in black-tailed prairie dogs to assess the generality of links between climate and plague occurrence found in previous analyses of human plague cases. We examined long-term data on climate and plague occurrence in prairie dog colonies within two study areas. Multiple regression analyses revealed that plague occurrence in prairie dogs was not associated with climatic variables in our Colorado study area. In contrast, plague occurrence was strongly associated with climatic variables in our Montana study area. The models with most support included a positive association with precipitation in April–July of the previous year, in addition to a positive association with the number of “warm” days and a negative association with the number of “hot” days in the same year as reported plague events. We conclude that the timing and magnitude of precipitation and temperature may affect plague occurrence in some geographic areas. The best climatic predictors of plague occurrence in prairie dogs within our Montana study area are quite similar to the best climatic predictors of human plague cases in the southwestern United States. This correspondence across regions and species suggests support for a (temperature-modulated) trophic-cascade model for plague, including climatic effects on rodent abundance, flea abundance, and pathogen transmission, at least in regions that experience strong climatic signals.     

Visual shape recognition with contour propagation

A neural architecture is presented that encodes the visual space inside and outside of a shape. The contours of a shape are propagated across an excitable neuronal map and fed through a set of orientation columns, thus creating a pattern which can be viewed as a vector field. This vector field is then burned as synaptic, directional connections into a propagation map, which will serve as a “shape map”. The shape map identifies its own, preferred input when it is translated, deformed, scaled and fragmented, and discriminates other shapes very distinctively. Encoding visual space is much more efficient for shape recognition than determining contour geometry only.     

The anatomy, physiology, acoustics and perception of speech: essential elements in analysis of the evolution of human speech

Inferences on the evolution of human speech based on anatomical data must take into account its physiology, acoustics and perception. Human speech is generated by the supralaryngeal vocal tract (SVT) acting as an acoustic filter on noise sources generated by turbulent airflow and quasi-periodic phonation generated by the activity of the larynx. The formant frequencies, which are major determinants of phonetic quality, are the frequencies at which relative energy maxima will pass through the SVT filter. Neither the articulatory gestures of the tongue nor their acoustic consequences can be fractionated into oral and pharyngeal cavity components. Moreover, the acoustic cues that specify individual consonants and vowels are “encoded”, i.e., melded together. Formant frequency encoding makes human speech a vehicle for rapid vocal communication. Non-human primates lack the anatomy that enables modern humans to produce sounds that enhance this process, as well as the neural mechanisms necessary for the voluntary control of speech articulation. The specific claims of Duchin (1990) are discussed.     

A stochastic model for chemosensory cell movement: application to neutrophil and macrophage persistence and orientation

Two central features of leukocyte chemosensory movement behavior demand fundamental theoretical understanding. In uniform concentrations of chemoattractant, these cells exhibit a persistent random walk, with a characteristic “persistence time” between significant changes in direction. In chemoattractant concentration gradients, they demonstrate a biased random walk, with an “orientation bias” characterizing the fraction of cells moving up the gradient. A coherent picture of cell-movement responses to chemoattractant requires that both the persistence time and the orientation bias be explained within a unifying framework. In this paper we offer the possibility that “noise” in the cellular signal perception/response mechanism can simultaneously account for these two key phenomena. In particular, we report on a stochastic mathematical model for cell locomotion based on kinetic fluctuations in chemoattractant receptor binding. This model proves to be capable of stimulating cell paths similar to those observed experimentally for two cell types examined to date: neutrophils and alveolar macrophages, under conditions of uniform chemoattractant concentrations as well as chemoattractant concentration gradients. Further, this model can quantitatively predict both cell persistence time and dependence of orientation bias on gradient size. The model also successfully predicts that an increase in persistence time is associated with a decrease in orientation for typical system parameter values, as is observed for alveolar macrophages in comparison to neutrophils. Thus, the concept of signal “noise” can quantitatively unify the major characteristics of leukocyte random motility and chemotaxis. The same level of noise large enough to account for the observed frequency of turning in uniform environments is simultaneously small enough to allow for the observed degree of directional bias in gradients. This suggests that chemosensory cell movement behavior may be based on a “usefully” imperfect integrated signal response system, which allows both random and directed searches under appropriate conditions.     

Perceptual Distortions in Pitch and Time Reveal Active Prediction and Support for an Auditory Pitch-Motion Hypothesis

A number of accounts of human auditory perception assume that listeners use prior stimulus context to generate predictions about future stimulation. Here, we tested an auditory pitch-motion hypothesis that was developed from this perspective. Listeners judged either the time change (i.e., duration) or pitch change of a comparison frequency glide relative to a standard (referent) glide. Under a constant-velocity assumption, listeners were hypothesized to use the pitch velocity (Δf/Δt) of the standard glide to generate predictions about the pitch velocity of the comparison glide, leading to perceptual distortions along the to-be-judged dimension when the velocities of the two glides differed. These predictions were borne out in the pattern of relative points of subjective equality by a significant three-way interaction between the velocities of the two glides and task. In general, listeners’ judgments along the task-relevant dimension (pitch or time) were affected by expectations generated by the constant-velocity standard, but in an opposite manner for the two stimulus dimensions. When the comparison glide velocity was faster than the standard, listeners overestimated time change, but underestimated pitch change, whereas when the comparison glide velocity was slower than the standard, listeners underestimated time change, but overestimated pitch change. Perceptual distortions were least evident when the velocities of the standard and comparison glides were matched. Fits of an imputed velocity model further revealed increasingly larger distortions at faster velocities. The present findings provide support for the auditory pitch-motion hypothesis and add to a larger body of work revealing a role for active prediction in human auditory perception.     

Comparison of the Antimicrobial Adhesion Potential of Human Body Fluid Glycoconjugates Using Fucose-Binding Lectin (PA-IIL) of Pseudomonas aeruginosa and Ulex europaeus Lectin (UEA-I)

Pseudomonas aeruginosa produces a fucose-binding lectin (PA-IIL) which strongly binds to human cells. This lectin was shown to be highly sensitive to inhibition by fucose-bearing human milk glycoproteins. Since the glycans of these glycoproteins mimic human cell receptors, they may function as decoys in blocking lectin-dependent pathogen adhesion to the host cells. Human saliva and seminal fluid also contain such compounds, and body fluids of individuals who are “secretors” express additional fucosylated (alpha 1,2) residues. The latter are selectively detected by Ulex europaeus lectin UEA-I. The aim of the present research was to compare the PA-IIL and UEA-I interactions with human salivas and seminal fluids of “secretors” and “nonsecretors” with those obtained with the respective milks. Using hemagglutination inhibition and Western blot analyses, we showed that PA-IIL interactions with the saliva and seminal fluid glycoproteins were somewhat weaker than those obtained with the milk and that “nonsecretor” body fluids were not less efficient than those of “secretors” in PA-IIL blocking. UEA-I, which interacted only with the “secretors” glycoproteins, was most sensitive to those of the seminal fluids.     

To Perceive or Not Perceive: The Role of Gamma-band Activity in Signaling Object Percepts

The relation of gamma-band synchrony to holistic perception in which concerns the effects of sensory processing, high level perceptual gestalt formation, motor planning and response is still controversial. To provide a more direct link to emergent perceptual states we have used holistic EEG/ERP paradigms where the moment of perceptual “discovery” of a global pattern was variable. Using a rapid visual presentation of short-lived Mooney objects we found an increase of gamma-band activity locked to perceptual events. Additional experiments using dynamic Mooney stimuli showed that gamma activity increases well before the report of an emergent holistic percept. To confirm these findings in a data driven manner we have further used a support vector machine classification approach to distinguish between perceptual vs. non perceptual states, based on time-frequency features. Sensitivity, specificity and accuracy were all above 95%. Modulations in the 30–75 Hz range were larger for perception states. Interestingly, phase synchrony was larger for perception states for high frequency bands. By focusing on global gestalt mechanisms instead of local processing we conclude that gamma-band activity and synchrony provide a signature of holistic perceptual states of variable onset, which are separable from sensory and motor processing.     

An Analysis of Vegetation Stripe Formation in Semi-Arid Landscapes

Vegetation stripes (“tiger bush”) are a characteristic feature of semi-arid environments. The stripes typically lie along the contours of gentle slopes, and some authors report a gradual uphill migration. A previous mathematical model (Klausmeier, Science, 284:1826, 1999) has shown that this phenomenon can be explained relatively simply by the downhill flow of rainwater coupled with the diffusive spread of the plant population. This paper presents a detailed analysis of pattern formation in the Klausmeier model. The author derives formulae for the wavelength and migration speed of the predicted patterns, and systematically investigates how these depend on model parameters. The results make new predictions and suggest possible approaches to testing the model.     

Is phospholipase A2 a “glucose sensor” responsible for the phasic pattern of insulin release?

The mechanisms involved in the characteristic, normal biphasic pattern of glucose-induced insulin release (which is grossly altered in type II diabetics) have not been definitely elucidated. However, the temporal pattern of arachidonic acid release induced by cellular phospholipases precisely mimics that of first-phase insulin release, both being characterized by a burst of release peaking near 2—3 minutes and followed by a “trough” or apparent refractory period most apparent at 5–10 minutes. The latter appears temporally related not only to decreased arachidonate release but also to stimulation of its re-esterification. Pancreatic islets contain a glucose-sensitive phospholipase A₂, and glucose has been shown to increase the accumulation of islet lipoxygenase-derived products which appear to be “third messengers” mediating insulin release. Blockade either of islet phospholiphase(s) or of islet lipoxygenase totally abrogates glucose-induced insulin release. The hypothesis is therefore proposed that phospholiphase A₂ could be one beta cell “glucose sensor”, and that the released arachidonate is coupled to an islet lipoxygenase. Labile oxygenated metabolites (lipid peroxides and epoxides) transduce the glucose signal into insulin release. The available data (albeit incomplete) are compatible with the formulation that the biphasic pattern of glucose-induced insulin release could be explained by dynamic changes in the availability of arachidonic acid and its consequent oxygenation.     

Dynamic Reweighting of Auditory Modulation Filters

Sound waveforms convey information largely via amplitude modulations (AM). A large body of experimental evidence has provided support for a modulation (bandpass) filterbank. Details of this model have varied over time partly reflecting different experimental conditions and diverse datasets from distinct task strategies, contributing uncertainty to the bandwidth measurements and leaving important issues unresolved. We adopt here a solely data-driven measurement approach in which we first demonstrate how different models can be subsumed within a common ‘cascade’ framework, and then proceed to characterize the cascade via system identification analysis using a single stimulus/task specification and hence stable task rules largely unconstrained by any model or parameters. Observers were required to detect a brief change in level superimposed onto random level changes that served as AM noise; the relationship between trial-by-trial noisy fluctuations and corresponding human responses enables targeted identification of distinct cascade elements. The resulting measurements exhibit a dynamic complex picture in which human perception of auditory modulations appears adaptive in nature, evolving from an initial lowpass to bandpass modes (with broad tuning, Q∼1) following repeated stimulus exposure.     

Some problems in mathematical biophysics of visual perception and aesthetics

The paper outlines a further extension of a previous theory. It discusses perception of straight lines, perception of length, perception of intersections, disconnected contours; effects of associations; breaking up of a pattern into parts; some suggestions for experimental procedure.     

Attentional selection in visual perception,memory and action: a quest for cross-domain integration

For decades, the cognitive and neural sciences have benefitted greatly from a separation of mind and brain into distinct functional domains. The tremendous success of this approach notwithstanding, it is self-evident that such a view is incomplete. Goal-directed behaviour of an organism requires the joint functioning of perception, memory and sensorimotor control. A prime candidate for achieving integration across these functional domains are attentional processes. Consequently, this Theme Issue brings together studies of attentional selection from many fields, both experimental and theoretical, that are united in their quest to find overreaching integrative principles of attention between perception, memory and action. In all domains, attention is understood as combination of competition and priority control (‘bias’), with the task as a decisive driving factor to ensure coherent goal-directed behaviour and cognition. Using vision as the predominant model system for attentional selection, many studies of this Theme Issue focus special emphasis on eye movements as a selection process that is both a fundamental action and serves a key function in perception. The Theme Issue spans a wide range of methods, from measuring human behaviour in the real word to recordings of single neurons in the non-human primate brain. We firmly believe that combining such a breadth in approaches is necessary not only for attentional selection, but also to take the next decisive step in all of the cognitive and neural sciences: to understand cognition and behaviour beyond isolated domains.     

Protein adsorption on histidyl-aminohexyl-Sepharose 4B: II. Application to the negative one-step affinity purification of human β2-microglobulin and Immunoglobulin G

The adsorption of two human proteins, β2-microglobulin and Immunoglobulin G, from uremic patient’s blood ultrafiltrate and plasma, respectively, was investigated on the histidyl-aminohexyl-Sepharose 4B adsorbent. Both target proteins could be adsorbed on the gel through a low affinity for immobilized histidine ligand. However, a fine adjustment of the operating conditions (ionic strength, buffer, pH) prevented their adsorption and thus allowed their “negative affinity” purification (purity estimated by silver nitrate SDS–PAGE) by the removal of the contaminating proteins. This simple and efficient method provides purification under gentle chromatographic conditions and a further characterization of both molecules.