Bands of brothers and in-laws: Waorani warfare, marriage and alliance formation.

The root of modern human warfare lies in the lethal coalitionary violence of males in small-scale societies. However, there is a paucity of quantitative data concerning the form and function of coalitionary violence in this setting. Debates exist over how lethal coalitions are constituted, as well as the motivations and benefits for males to join such groups. Data from a lowland Amazonian population, the Waorani of Ecuador, illuminate three issues: (i) the degree to which raiding parties are composed of groups of fraternal kin as opposed to strategic alliances of actual or potential affinal kin; (ii) the extent to which individuals use pre-existing affinal ties to motivate others to participate in war or leverage warfare as a mechanism to create such ties; and (iii) the extent to which participation in raiding is driven by rewards associated with future marriage opportunities. Analyses demonstrate that Waorani raiding parties were composed of a mix of males who were potential affines, actual affines and fraternal kin, suggesting that men used pre-existing genetic, lineal and social kin ties for recruiting raid partners and used raiding as a venue to create novel social relationships. Furthermore, analyses demonstrate that males leveraged raiding alliances to achieve marriage opportunities for themselves as well as for their children. Overall, it appears that a complex set of motivations involving individual rewards, kin marriage opportunities, subtle coercion and the assessment of alliance strength promote violent intergroup conflict among the Waorani. These findings illustrate the complex inter-relationships among kin selection, coalition building and mating success in our species.

The cultural shaping of revenge.

There are interesting parallelisms between McCullough et al.'s article and studies of revenge presented by French legal anthropologist Raymond Verdier, particularly as regards the discussion of the increasing likelihood of revenge with increasing social distance. Additionally, the observation that many peoples speak of revenge in the language of debt and repayment, links it with exchanges of benefits as well as costs.

Life histories, blood revenge, and reproductive success among the Waorani of Ecuador.

The Waorani may have the highest rate of homicide of any society known to anthropology. We interviewed 121 Waorani elders of both sexes to obtain genealogical information and recollections of raids in which they and their relatives participated. We also obtained complete raiding histories of 95 warriors. An analysis of the raiding histories, marital trajectories, and reproductive histories of these men reveals that more aggressive warriors have lower indices of reproductive success than their milder brethren. This result contrasts the findings of Chagnon [Chagnon N (1988) Science 239:985-992] for the Yanomamo. We suggest that the spacing of revenge raids may be involved in the explanation of why the consequences of aggressiveness differ between these 2 warlike lowland South American peoples.

The life history of human foraging: Cross-cultural and individual variation.

Human adaptation depends on the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring hunters' increases and declines of skill from approximately 23,000 hunting records generated by more than 1800 individuals at 40 locations. The data reveal an average age of peak productivity between 30 and 35 years of age, although high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more on heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the coevolution of human life history and cultural adaptation.

The Proximate Causes of Waorani Warfare.

In response to recent work on the nature of human aggression, and to shed light on the proximate, as opposed to ultimate, causes of tribal warfare, we present a record of events leading to a fatal Waorani raid on a family from another tribe, followed by a detailed first-person observation of the behavior of the raiders as they prepared themselves for war, and upon their return. We contrast this attack with other Waorani aggressions and speculate on evidence regarding their hormonal underpinnings. On-the-ground ethnographic observations are examined in light of the neuroendocrinological literature. The evidence suggests a chain of causality in launching lethal violence, beginning with a perceived injury, culminating in a massacre, and terminating in rejoicing. Although no blood or saliva samples were taken at the time of this raid, the behaviors were consistent with a deliberate initiation of the hormonal cascade characterizing the "fight-or-flight" response, along with other hormonal changes. We conclude with observations on the stratified interrelationships of the cognitive, social, emotional, and neuroendocrinological causes of aggression leading to coalitional male homicide.

Testing safety eyewear: how frame and lens design affect lens retention.

PURPOSE: The aim of this study was to determine the role that frame and lens design play in lens retention during high-impact testing of safety eyewear that advertises conformance to the performance-based ANSI Z87.1-2003 standard. METHODS: A total of 75 Z87 safety eyeglass frames (3 each of 25 frame models) were used in this study, procured from 5 of the leading U.S. safety frame manufacturers. Frames were fitted by an independent laboratory with 2.0-mm plano polycarbonate lenses in compliance with ANSI Z87.1-2003. Finished spectacles were sent to a subsequent laboratory testing facility where each frame was subjected to both high-mass and oblique-incidence high-velocity impacts to determine frame characteristics that were most highly associated with testing failure. Among the frame and lens parameters that were considered in this analysis were the A and B dimensions, effective diameter, distance between lenses, bridge type, frame material, bevel type, and frame cost. Certain variables were controlled for by maintaining consistency among all spectacle pairs, e.g., lens prescription, center thickness, and edge thickness. Multiple logistic regression was used to control potential confounding variables and to develop the best combination of them for predictive value. RESULTS: Of 25 separate frame models assessed, 10 passed both high-mass and high-velocity impact testing, i.e., none of the 3 frame/lens samples failed. Of the models that failed, 13 failures were caused by high-velocity testing, 1 by high-mass testing, and 1 failed both high-mass and high-velocity testing. None of the 15 spectacles with the SprinGuardtrade mark (Hilco, Plainville, Massachusetts) bevel design failed, although these were proprietary to 1 manufacturer and included only 5 frame models. Two spectacle designs (6 individual frames) incorporated an inverted bevel design of which 3 of the frames failed impact testing. Controlling for drop ball velocity among the 54 remaining standard "V" bevel spectacle pairs, the odds of failure were about 8 to 9 times higher for metal frames than Zylonite frames (odds ratio [OR], 8.5; 95% confidence interval [CI], 1.4 to 52.3; P = 0.02), and the odds of failure were about 4 times higher for lens effective diameters of less than 50 mm than for lens effective diameters more than 50 mm (OR, 4.1; 95% CI, 1.2 to 14.8; P = 0.03). CONCLUSION: Among our sample of safety spectacles, failure from high-mass impact resistance testing rarely occurred. No spectacles with the SprinGuard bevel design failed in our analysis, but this was limited to a small sample size from a single manufacturer. Among our sample of 54 spectacle pairs with a v-bevel design, metal frame material and an effective diameter of less than 50 mm were the strongest predictors of failure relative to high-velocity impact testing with a 45 degrees temporal angle projectile.

Micro and regular saccades across the lifespan during a visual search of "Where's Waldo" puzzles.

Despite the fact that different aspects of visual-motor control mature at different rates and aging is associated with declines in both sensory and motor function, little is known about the relationship between microsaccades and either development or aging. Using a sample of 343 individuals ranging in age from 4 to 66 and a task that has been shown to elicit a high frequency of microsaccades (solving Where's Waldo puzzles), we explored microsaccade frequency and kinematics (main sequence curves) as a function of age. Taking advantage of the large size of our dataset (183,893 saccades), we also address (a) the saccade amplitude limit at which video eye trackers are able to accurately measure microsaccades and (b) the degree and consistency of saccade kinematics at varying amplitudes and directions. Using a modification of the Engbert-Mergenthaler saccade detector, we found that even the smallest amplitude movements (0.25-0.5°) demonstrate basic saccade kinematics. With regard to development and aging, both microsaccade and regular saccade frequency exhibited a very small increase across the life span. Visual search ability, as per many other aspects of visual performance, exhibited a U-shaped function over the lifespan. Finally, both large horizontal and moderate vertical directional biases were detected for all saccade sizes.

Sports vision testing of selected athletic participants in the 1997 and 1998 AAU Junior Olympic Games.

BACKGROUND: Sports vision researchers have attempted to establish the need for vision care services for athletes and the relationship between visual skills and athletic success. METHODS: Data collected from sports vision screenings at the 1997 and 1998 Amateur Athletic Union AAU Junior Olympic Games was compiled for analysis. Four hundred forty-nine athletes, ranging in ages from 5 to 19 years old and representing 12 sports, were part of the sports vision epidemiology project conducted by the American Optometric Association Sports Vision Section. Protocols from the AOA Sports Vision Section were used to assess the visual systems of athletes participating in the games. The history included evaluation of the use of vision care services, refractive correction type, and symptomology. The screening assessed visual acuity, contrast sensitivity, ocular alignment, eye-hand dominance, handspeed, footspeed, speed of stereopsis, speed of recognition, eye movements, hand-eye coordination, anterior-segment health, and posterior-segment health. Performance testing was analyzed by age group and sport. RESULTS: In this population of athletes, eye care was under-utilized. The performance testing indicated an increase in performance with increasing age for most tests. With increasing age, there was a decrease in the number of fixation losses, an increase in footspeed, and a decrease in handspeed. The norms for the performance tests are reported by age group and by sport. CONCLUSIONS: The results of this study imply that athletic populations at all levels are in need of eye care services. The norms derived from this investigation act as a standard for the evaluation of vision performance using the AOA Sports Vision Testing Battery.