Peak shift

Background
The peak shift model predicts that the age-profile of a pathogen's prevalence depends upon its transmission rate, peaking earlier in populations with higher transmission and declining as partial immunity is acquired. Helminth infections are associated with increased immunoglobulin E (IgE), which may convey partial immunity and influence the peak shift. Although studies have noted peak shifts in helminths, corresponding peak shifts in total IgE have not been investigated, nor has the age-patterning been carefully examined across populations. We test for differences in the age-patterning of IgE between two South American forager-horticulturalist populations and the United States: the Tsimane of Bolivia (n = 832), the Shuar of Ecuador (n = 289), and the U.S. NHANES (n = 8,336). We then examine the relationship between total IgE and helminth prevalences in the Tsimane.

Methodology/Principal Findings
Total IgE levels were assessed in serum and dried blood spots and age-patterns examined with non-linear regression models. Tsimane had the highest IgE (geometric mean = 8,182 IU/ml), followed by Shuar (1,252 IU/ml), and NHANES (52 IU/ml). Consistent with predictions, higher population IgE was associated with steeper increases at early ages and earlier peaks: Tsimane IgE peaked at 7 years, Shuar at 10 years, and NHANES at 17 years. For Tsimane, the age-pattern was compared with fecal helminth prevalences. Overall, 57% had detectable eggs or larva, with hookworm (45.4%) and Ascaris lumbricoides (19.9%) the most prevalent. The peak in total IgE occurred around the peak in A. lumbricoides, which was associated with higher IgE in children <10, but with lower IgE in adolescents.

Conclusions
The age-patterning suggests a peak shift in total IgE similar to that seen in helminth infections, particularly A. lumbricoides. This age-patterning may have implications for understanding the effects of helminths on other health outcomes, such as allergy, growth, and response to childhood vaccination.

One image dominates our contemporary world above all others: the human body. How Art Made the World travels from the modern world of advertising to the temples of classical Greece and the tombs of ancient Egypt to solve the mystery of why humans surround themselves with images of the body that are so unrealistic.

The main theme of this episode is how people rarely created images of the body that are realistic. By understanding this we  also understand something about our bodies, and human nature in general.

The Venus of Willendorf, in the Natural History Museum in Vienna, is a small Venus figure with exaggerated breasts, hips and sexual organs. These exaggerations are symbolic of fertility,  what is significant is that the artist ignored other parts of the body, such as her face and arms. Similar Venus figures with similar exaggerations and omissions have been found all over Europe and Russia. Professor Ramachandran explains why features were exaggerated. By making comparisons to research with Herring Gulls showing how their chicks, which are stimulated by the red stripe on their parents beaks, can be over stimulated by simulating a beak with additional stripes. He suggests that the same neurological process stimulated early man, explaining why they exaggerated these features of fertility over others.

Moving forward several thousand years. The Egyptians, who valued consistency and order in their society, abandoned the exaggerations of their ancestors and chose to use a mathematical approach to creating images of the body. They chose to show each part of the body from it’s clearest angle, developing their recognisable style and then preserving this style for thousands of years. When the Ancient Greek’s culture came into contact with the Egyptians, this ignited an artistic revolution across the Greek city states. The Greek culture wanted a more realistic representation of the figure for their temples, and as with the Kritios Boy, they measured and reproduced the body to exact dimensions in their sculptures. A generation later, however, the Greeks abandoned this ultra realism preferring exaggerated representations of the body based on the aestetic theories created by Polykleitos, such as the Riace Bronzes. Prof Ramachandran explains that art needs this exaggeration to be interesting.

The programme concludes with what we choose to exaggerate, saying this  “is where the magic comes in”. The choice of what to exaggerate has changed over the centuries to match changing human values.

Natural and augmented breasts differ in size and shape. Natural breasts are characterized by concave-to-straight upper-pole contours while augmented breasts are fuller and therefore may have convex upper-pole contours, irrespective of their size. The hypothesis that augmented breasts in a range of cup sizes are rated significantly more attractive than naturalistic breasts was investigated and confirmed using computer generated images of breasts in lateral-view by all males and females cross-culturally in English and Farsi speaking samples. Correlations were then used to show that, for all participants, breast area and breast displacement (concavity or convexity) are positively correlated with attractiveness ratings for natural but not augmented breasts. These results are counter-intuitive since humans could not have evolved in environments that included augmented breasts. The findings are introduced using the ethological concept of supernormal stimuli and the behaviorist/neuroaesthetic principle, the peak shift effect, applied to secondary sexual characteristics (i.e., waist-hip ratios and breasts) and it is concluded that augmented breasts, though deceptive signals of fertility, are supernormal stimuli.

Men are attracted to the movements of women's bodies. The aim of this paper is to answer the question: what is the mechanism? The role of the peak shift effect in perceptions of physical attractiveness involving women‟s waist-to-hip ratios (WHRs) in biological motion is presented. Photographs of a coordinated motor pattern, walking, are investigated with a novel measurement method. Evidence is presented that the behavior pattern contains alternating left and right side, attractive (S+) and unattractive (S-), WHR stimuli. A WHR stimulus range is established that is sufficient to generate peak shift effects in perceptions of physical attractiveness. It is predicted that WHRs in attractive behavior patterns will be significantly lower than those previously found to be preferred using 0.70 WHR still images. Therefore WHRs in motion represent S++, or “supernormal stimuli”, in behavior.

To gain understanding of the perceived components of waist-to-hip ratios in various viewing perspectives, patrons of an exotic dance club were asked to rate physical attractiveness of photographs of a woman with an actual waist-to-hip ratio (actual-WHR) of 0.70 in two conditions: squared-stance and contrapposto pose. These photographs were taken at 45° incremental rotations in frontal, front-profile, side, posterior-profile and posterior views. The images were also divided along medially-placed vertical centerlines and presented in pairs to be individually rated. Results of this pilot study indicate that; 1) the contrapposto pose photos are rated significantly higher than squared-stance photos, 2) original photographs are rated significantly higher than divided photographs, 3) for both sets of paired images, the sides showing the lower, right or left side WHRs scored significantly higher. These results support the hypothesis that view-dependent WHRs are differently rated than actual-WHRs, and are perceived components (i.e., S+, S- and S++ stimuli) of physically attractive photographs. Implications of these findings are discussed in regard to the peak shift effect, phylogenetic adaptation and ontogenetic attunement in a model incorporating signal detection theory.

Men are attracted to the movements of women's bodies. The aim of this paper is to answer the question: what is the mechanism? The role of the peak shift effect in perceptions of physical attractiveness involving women's waist-to-hip ratios (WHRs) in biological motion is presented. Photographs of a coordinated motor pattern, walking, are investigated with a novel measurement method. Evidence is presented that the behavior pattern contains alternating left and right side, attractive (S+) and unattractive (S-), WHR stimuli. The presence of a WHR stimulus range that is sufficient to generate a peak shift effect in perceptions of physical attractiveness is established. It is predicted that WHRs in attractive behavior patterns will be significantly lower than those previously found to be preferred using 0.70 WHR still images. Therefore WHRs in motion represent S++, or "supernormal stimuli", in behavior.

Three experiments investigated temporal generalization in humans. In Experiment 1, a peak shift effect was produced when participants were given intradimensional discrimination training. In Experiment 2, after training with a standard S+ and generalization testing with an asymmetrical series of durations, generalization gradients moved toward the prevailing adaptation level. In Experiment 3, generalization gradients showed a central tendency shift and moved away from the S+ and toward the mean of the test series (of 11 stimulus durations) after participants received training with S+ and S- durations that in one condition were the 2nd and 4th and in another condition were the 4th and 2nd stimuli in the series, respectively. The results were inconsistent with an absolute account of peak shift but were consistent with an adaptation level account of peak shift.

Background: The peak shift model predicts that the age-profile of a pathogen's prevalence depends upon its transmission rate, peaking earlier in populations with higher transmission and declining as partial immunity is acquired. Helminth infections are associated with increased immunoglobulin E (IgE), which may convey partial immunity and influence the peak shift. Although studies have noted peak shifts in helminths, corresponding peak shifts in total IgE have not been investigated, nor has the age-patterning been carefully examined across populations. We test for differences in the agepatterning of IgE between two South American forager-horticulturalist populations and the United States: the Tsimane of Bolivia (n = 832), the Shuar of Ecuador (n = 289), and the U.S. NHANES (n = 8,336). We then examine the relationship between total IgE and helminth prevalences in the Tsimane.