An assessment of the likely impact of strain-related phenotypic plasticity on hominin fossil species identification

It has been proposed that strain-related phenotypic plasticity may be a major confounding factor in attributing hominin fossils to species. The study reported here tested this hypothesis with craniometric data from the great apes and Colobus guereza. We divided the measurements into three groups: measurements of features subject to high masticatory strain, measurements of features subject to low-to-moderate masticatory strain, and measurements of features that do not remodel and therefore are not prone to strain-related phenotypic plasticity. Next, we used the coefficient of variation and ANOVA to investigate whether masticatory strain is a cause of variability. These analyses partially supported the hypothesis. The predicted differences between the high-strain measurements and the other measurements were found in the majority of the species. However, the coefficient of variation values for the low-to-moderate strain and non-phenotypically plastic measurements were indistinguishable. Thereafter, we used discriminant function analysis to compare the ability of the three groups of measurements to assign specimens to species. This analysis did not support the hypothesis. The high-strain measurements were less effective than the other measurements, but the low-to-moderate strain measurements were more effective than the non-phenotypically plastic measurements. In addition, better discrimination was achieved when all the measurements were employed than when just the non-phenotypically plastic measurements were utilised. We conclude from this that strain-related phenotypic plasticity is unlikely to impede hominin alpha taxonomic research

An assessment of the likely impact of strain-related phenotypic plasticity on hominin fossil species identification

It has been proposed that strain-related phenotypic plasticity may be a major confounding factor in attributing hominin fossils to species. The study reported here tested this hypothesis with craniometric data from the great apes and Colobus guereza. We divided the measurements into three groups: measurements of features subject to high masticatory strain, measurements of features subject to low-to-moderate masticatory strain, and measurements of features that do not remodel and therefore are not prone to strain-related phenotypic plasticity. Next, we used the coefficient of variation and ANOVA to investigate whether masticatory strain is a cause of variability. These analyses partially supported the hypothesis. The predicted differences between the high-strain measurements and the other measurements were found in the majority of the species. However, the coefficient of variation values for the low-to-moderate strain and non-phenotypically plastic measurements were indistinguishable. Thereafter, we used discriminant function analysis to compare the ability of the three groups of measurements to assign specimens to species. This analysis did not support the hypothesis. The high-strain measurements were less effective than the other measurements, but the low-to-moderate strain measurements were more effective than the non-phenotypically plastic measurements. In addition, better discrimination was achieved when all the measurements were employed than when just the non-phenotypically plastic measurements were utilised. We conclude from this that strain-related phenotypic plasticity is unlikely to impede hominin alpha taxonomic research

Considering the role of time budgets on copy-error rates in material culture traditions: An experimental assessment

Ethnographic research highlights that there are constraints placed on the time available to produce cultural artefacts in differing circumstances. Given that copying error, or cultural ‘mutation’, can have important implications for the evolutionary processes involved in material culture change, it is essential to explore empirically how such ‘time constraints’ affect patterns of artefactual variation. Here, we report an experiment that systematically tests whether, and how, varying time constraints affect shape copying error rates. A total of 90 participants copied the shape of a 3D ‘target handaxe form’ using a standardized foam block and a plastic knife. Three distinct ‘time conditions’ were examined, whereupon participants had either 20, 15, or 10 minutes to complete the task. One aim of this study was to determine whether reducing production time produced a proportional increase in copy error rates across all conditions, or whether the concept of a task specific ‘threshold’ might be a more appropriate manner to model the effect of time budgets on copy-error rates. We found that mean levels of shape copying error increased when production time was reduced. However, there were no statistically significant differences between the 20 minute and 15 minute conditions. Significant differences were only obtained between conditions when production time was reduced to 10 minutes. Hence, our results more strongly support the hypothesis that the effects of time constraints on copying error are best modelled according to a ‘threshold’ effect, below which mutation rates increase more markedly. Our results also suggest that ‘time budgets’ available in the past will have generated varying patterns of shape variation, potentially affecting spatial and temporal trends seen in the archaeological record. Hence, ‘time-budgeting’ factors need to be given greater consideration in evolutionary models of material culture change

An Experimental Test of the Accumulated Copying Error Model of Cultural Mutation for Acheulean Handaxe Size

Archaeologists interested in explaining changes in artifact morphology over long time periods have found it useful to create models in which the only source of change is random and unintentional copying error, or ‘cultural mutation’. These models can be used as null hypotheses against which to detect non-random processes such as cultural selection or biased transmission. One proposed cultural mutation model is the accumulated copying error model, where individuals attempt to copy the size of another individual's artifact exactly but make small random errors due to physiological limits on the accuracy of their perception. Here, we first derive the model within an explicit mathematical framework, generating the predictions that multiple independently-evolving artifact chains should diverge over time such that their between-chain variance increases while the mean artifact size remains constant. We then present the first experimental test of this model in which 200 participants, split into 20 transmission chains, were asked to faithfully copy the size of the previous participant's handaxe image on an iPad. The experimental findings supported the model's prediction that between-chain variance should increase over time and did so in a manner quantitatively in line with the model. However, when the initial size of the image that the participants resized was larger than the size of the image they were copying, subjects tended to increase the size of the image, resulting in the mean size increasing rather than staying constant. This suggests that items of material culture formed by reductive vs. additive processes may mutate differently when individuals attempt to replicate faithfully the size of previously-produced artifacts. Finally, we show that a dataset of 2601 Acheulean handaxes shows less variation than predicted given our empirically measured copying error variance, suggesting that other processes counteracted the variation in handaxe size generated by perceptual cultural mutation

Genesis and spread of multiple reassortants during the 2016/2017 H5 avian influenza epidemic in Eurasia.

Highly pathogenic avian influenza (HPAI) viruses of the H5 A/goose/Guangdong/1/96 lineage can cause severe disease in poultry and wild birds, and occasionally in humans. In recent years, H5 HPAI viruses of this lineage infecting poultry in Asia have spilled over into wild birds and spread via bird migration to countries in Europe, Africa, and North America. In 2016/2017, this spillover resulted in the largest HPAI epidemic on record in Europe and was associated with an unusually high frequency of reassortments between H5 HPAI viruses and cocirculating low-pathogenic avian influenza viruses. Here, we show that the seven main H5 reassortant viruses had various combinations of gene segments 1, 2, 3, 5, and 6. Using detailed time-resolved phylogenetic analysis, most of these gene segments likely originated from wild birds and at dates and locations that corresponded to their hosts’ migratory cycles. However, some gene segments in two reassortant viruses likely originated from domestic anseriforms, either in spring 2016 in east China or in autumn 2016 in central Europe. Our results demonstrate that, in addition to domestic anseriforms in Asia, both migratory wild birds and domestic anseriforms in Europe are relevant sources of gene segments for recent reassortant H5 HPAI viruses. The ease with which these H5 HPAI viruses reassort, in combination with repeated spillovers of H5 HPAI viruses into wild birds, increases the risk of emergence of a reassortant virus that persists in wild bird populations yet remains highly pathogenic for&nbsp;poultry.</p