Human Communication Systems Evolve by Cultural Selection

Human communication systems, such as language, evolve culturally; their components undergo reproduction and variation. However, a role for selection in cultural evolutionary dynamics is less clear. Often neutral evolution (also known as 'drift') models, are used to explain the evolution of human communication systems, and cultural evolution more generally. Under this account, cultural change is unbiased: for instance, vocabulary, baby names and pottery designs have been found to spread through random copying. While drift is the null hypothesis for models of cultural evolution it does not always adequately explain empirical results. Alternative models include cultural selection, which assumes variant adoption is biased. Theoretical models of human communication argue that during conversation interlocutors are biased to adopt the same labels and other aspects of linguistic representation (including prosody and syntax). This basic alignment mechanism has been extended by computer simulation to account for the emergence of linguistic conventions. When agents are biased to match the linguistic behavior of their interlocutor, a single variant can propagate across an entire population of interacting computer agents. This behavior-matching account operates at the level of the individual. We call it the Conformity-biased model. Under a different selection account, called content-biased selection, functional selection or replicator selection, variant adoption depends upon the intrinsic value of the particular variant (e.g., ease of learning or use). This second alternative account operates at the level of the cultural variant. Following Boyd and Richerson we call it the Content-biased model. The present paper tests the drift model and the two biased selection models' ability to explain the spread of communicative signal variants in an experimental micro-society

Fetal Programming and Fetal Psychology

The introduction of the ‘fetal programming hypothesis’, first in epidemiology, subsequently in a broad range of disciplines concerned with developmental biology, has generated new interest in phenotypic plasticity, the mechanisms that govern it, and its place in evolutionary biology. A number of epidemiological studies link small size at birth, assumed to be a consequence of constrained prenatal energy availability, with adverse effects on the risk of chronic diseases later in life. The cluster of chronic diseases associated with the metabolic syndrome and alterations of glucose metabolism are particularly implicated. Recent evidence suggests that epigenetic modification of gene expression affecting the hypothalamic-pituitary-adrenal (HPA) axis may be involved in these effects. In animal studies epigenetic alteration of HPA axis activity and responsiveness is associated with changes in adult behaviour and stress responsiveness. The potential for similar effects to contribute to psychological and psychiatric outcomes in humans has been explored in a number of contexts, including famine exposure, observed covariance with birth weight, and prenatal dexamethasone treatment of fetuses at risk of congenital adrenal hyperplasia. While fetal programming effects have now been widely demonstrated across species and human populations, the adaptive significance of these effects is still a matter of debate.Human Evolutionary Biolog

Life Historical Perspectives on Human Reproductive Aging

A commentary is offered on the chapters that comprise the section on Theoretical Foundations, emphasizing novel contributions of each. Three additional points are then made. First, while the biology of reproductive aging may be common to all human populations, its actual course can be expected to vary between individuals and between populations depending on ecological conditions and developmental histories. Second, increasing fertility (such as that typical of humans compared with hominoid relatives and imputed ancestral species) decreases the opportunity and impact of contributions from ascendant relatives and increases the opportunity and impact of contributions from collateral and descendent relatives in promoting the fitness of a focal individual. Finally, an argument is made that the major change in human life history physiology in the Pleistocene has been the extension of adult lifespan, not any change in ovarian physiology or rate of reproductive senescence, and that extended lifespan created a selection pressure for the emergence of indirect reproductive effort among postreproductive individuals, not the reverse.AnthropologyHuman Evolutionary Biolog

The involvement of posterior parietal cortex in feature and conjunction visuomotor search.

Successful interaction with the environment often involves the identification and localization of a particular item. Right posterior parietal cortex (rPPC) is necessary for the successful completion of conjunction but not feature visual search, regardless of the attentional requirements. One account for this dissociation is that rPPC is primarily involved in processing spatial information. For target identification, conjunction tasks require that spatial information is used to determine if features occur at the same location, whilst feature search does not require such a process. This account suggests that if the requirement to localize the target is made explicit then rPPC may also be necessary for feature search. This was examined using transcranial magnetic stimulation (TMS) and by manipulating the response mode: participants were either required to press a button indicating the presence/absence of the target, or else had to point to the target. TMS over rPPC did not disrupt performance of the feature task when a button-press was required, but significantly increased response time and movement time for the same task in the pointing condition. Conjunction search in both response conditions was significantly impaired by TMS. Performance on a task which required pointing to a target in the absence of distractors, and thus did not involve visual search, was unaffected by rPPC stimulation. We conclude that rPPC is involved in coding and representing spatial information, and is therefore crucial when the task requires determining whether or not two features spatially co-occur, or when search is combined with explicit target localization via a visuomotor transformation

Transverse Beam Dynamics with Noise

The linear transverse beam dynamics perturbed by magnet non-linearities and noise is analysed, using averaging techniques

Emittance Growth Due To Tune Fluctuations and the Beam-beam interaction

Analytical formulae and computer simulation results are presented for the emittance growth caused by small asymmetries of the beam-beam force, caused by small fluctuations of the phase, small offsets between the beams and fluctuations in the size of the opposite beam

Concordant cues in faces and voices: testing the backup signal hypothesis

Information from faces and voices combines to provide multimodal signals about a person. Faces and voices may offer redundant, overlapping (backup signals), or complementary information (multiple messages). This article reports two experiments which investigated the extent to which faces and voices deliver concordant information about dimensions of fitness and quality. In Experiment 1, participants rated faces and voices on scales for masculinity/femininity, age, health, height, and weight. The results showed that people make similar judgments from faces and voices, with particularly strong correlations for masculinity/femininity, health, and height. If, as these results suggest, faces and voices constitute backup signals for various dimensions, it is hypothetically possible that people would be able to accurately match novel faces and voices for identity. However, previous investigations into novel face–voice matching offer contradictory results. In Experiment 2, participants saw a face and heard a voice and were required to decide whether the face and voice belonged to the same person. Matching accuracy was significantly above chance level, suggesting that judgments made independently from faces and voices are sufficiently similar that people can match the two. Both sets of results were analyzed using multilevel modeling and are interpreted as being consistent with the backup signal hypothesis