Stonehenge remodelled

We are pleased to present the latest account of the sequence of burial and construction at the site of Stonehenge, deduced by its most recent excavators and anchored in time by the application of Bayesian radiocarbon modelling. Five prehistoric stages are proposed, of varied duration, and related by our authors to neighbouring monuments in the Stonehenge environs. While it may never be possible to produce a definitive chronology for this most complex of monuments, the comprehensive and integrated achievement owed to these researchers has brought us much closer to that goal. It is from this firm platform that Stonehenge can begin its new era of communication with the public at large

Gamete competition, gamete limitation, and the evolution of the two sexes

Males and females are a fundamental aspect of human reproduction, yet procreation is perfectly possible without this division into two sexes. Biologically, males are defined as the sex that produces the smaller gametes (e.g. sperm), implying that the male and female sexes only exist in species with gamete dimorphism (anisogamy). Our ancestors were isogamous, meaning that only one gamete size was produced. The question of the evolutionary origin of males and females is then synonymous to asking what evolutionary pressures caused gamete sizes to diverge. Studying the ancestral evolutionary divergence of males and females relies largely on mathematical modelling. Here, we review two classes of models explaining the evolutionary origin of males and females: gamete competition and gamete limitation. These seemingly alternative explanations are not mutually exclusive, but two aspects of a single evolutionary process. Once evolved, anisogamy and the two sexes are evolutionarily very stable. This explains the maintenance of anisogamy in organisms with internal fertilization, which can cause large decreases in both gamete competition and gamete limitation. The ancestral divergence and maintenance of gamete sizes subsequently led to many other differences we now observe between the two sexes, sowing the seeds for what we have becom

Adaptive division of growth and development between hosts in helminths with two‐host life cycles

Parasitic worms (helminths) with complex life cycles divide growth and development between successive hosts. Using data from 597 species of acanthocephalans, cestodes, and nematodes with two‐host life cycles, we found that helminths with larger intermediate hosts were more likely to infect larger, endothermic definitive hosts, although some evolutionary shifts in definitive host mass occurred without changes in intermediate host mass. Life‐history theory predicts parasites to shift growth to hosts in which they can grow rapidly and/or safely. Accordingly, helminth species grew relatively less as larvae and more as adults if they infected smaller intermediate hosts and/or larger, endothermic definitive hosts. Growing larger than expected in one host, relative to host mass/endothermy, was not associated with growing less in the other host, implying a lack of cross‐host trade‐offs. Rather, some helminth orders had both large larvae and large adults. Within these taxa, however, size at maturity in the definitive host was unaffected by changes to larval growth, as predicted by optimality models. Parasite life‐history strategies were mostly (though not entirely) consistent with theoretical expectations, suggesting that helminths adaptively divide growth and development between the multiple hosts in their complex life cycles.Peer Reviewe

Perceived Exercise Benefits and Barriers of Non-Exercising Female University Students in the United Kingdom

Many individuals do not engage in sufficient physical activity due to low perceived benefits and high perceived barriers to exercise. Given the increasing incidence of obesity and obesity related health disorders, this topic requires further exploration. We used the Exercise Benefits/Barriers Scale to assess perceived benefit and barrier intensities to exercise in 200 non-exercising female university students (mean age 19.3 years, SD = 1.06) in the UK. Although our participants were selected because they self reported themselves to be non-exercising, however they reported significantly higher perceived benefits from exercise than perceived barriers to exercise [t(199) = 6.18, p < 0.001], and their perceived benefit/barrier ratio was 1.33. The greatest perceived benefit from exercise was physical performance followed by the benefits of psychological outlook, preventive health, life enhancement, and then social interaction. Physical performance was rated significantly higher than all other benefits. Psychological outlook and preventive health were not rated significantly different, although both were significantly higher than life enhancement and social interaction. Life enhancement was also rated significantly higher than social interaction. The greatest perceived barrier to exercise was physical exertion, which was rated significantly higher than time expenditure, exercise milieu, and family discouragement barriers. Implications from this investigation for the design of physical activity programmes include the importance, for females, of a perception of high benefit/barrier ratio that could be conducive to participation in exercise. Applied interventions need to assist female students to ‘disengage’ from or overcome any perceived ‘unpleasantness’ of physical exertion during physical activity (decrease their perceived barriers), and to further highlight the multiple health and other benefits of regular exercising (increase their perceived benefits)

Mandated Platform Compatibility: Competition and Welfare effects

Regulators have emphasized on mandating compatibility between competing platform ecosystems. In this paper, we study the welfare implications of compatibility by building a stylized model that reflects the competitive dynamics of the current mobile ecosystems market. We consider a device funded and an ad-funded platform that compete for attracting developers and consumers. If compatibility is mandated on the developer side in a way that eliminates the cost of developers to multi-home, then mandated compatibility reduces the welfare of both consumers and developers because it introduces strategic complementarities that limit platform competition for developers. As a result, developers are charged higher prices which through network externalities imply that also consumers are worse off. If compatibility is mandated on the consumer side, by allowing consumers to multi-home, then under strong network effects it can be a Pareto improvement and result in a win-win outcome for all market participants

Three Routes Forward For Biofuels: Incremental, Transitional, and Leapfrog

Besides the authors of this paper, many other people from the Sustainable Transportation Energy Pathways (NextSTEPS) research consortium assisted in the underlying analysis and internal review. This includes, but is not limited to, Joan Ogden, Steve Kaffka, Rich Plevin, Mark Delucchi, Sonia Yeh, Colin Murphy, and Paul Gruber. The NextSTEPS biofuels team wishes to thank representatives of the California Energy Commission (CEC) and the California Air Resources Board (ARB) for their valuable comments during a recent presentation of this work. The team also wishes to thank the NextSTEPS consortium members for their intellectual contributions and support of this researc

How to Best Automate Intersection Management

Recently there has been increased research interest in developing adaptive control systems for autonomous vehicles. This study presents a comparative evaluation of two distinct approaches to automated intersection management for a multiagent system of autonomous vehicles. The first is a centralized heuristic control approach using an extension of the Autonomous Intersection Management (AIM) system. The second is a decentralized neuro-evolution approach that adapts vehicle controllers so as they collectively navigate intersections. This study tests both approaches for controlling groups of autonomous vehicles on a network of interconnected intersections, without the constraints of traffic lights or stop signals. These task environments thus simulate potential future scenarios where vehicles must drive autonomously without specific road infrastructure constraints. The capability of each approach to appropriately handle various types of interconnected intersections, while maintaining an efficient throughput of vehicles and minimizing delay is tested. Results indicate that neuro-evolution is an effective method for automating collective driving behaviors that are robust across a broad range of road networks, where evolved controllers yield comparable task performance or out-perform an AIM controller