Chromosomes are likely to have assembled from unlinked genes in early evolution. Genetic linkage reduces the assortment load and intragenomic conflict in reproducing protocell models to the extent that chromosomes can go to fixation even if chromosomes suffer from a replicative disadvantage, relative to unlinked genes, proportional to their length. Here we numerically show that chromosomes spread within protocells even if recurrent deleterious mutations affecting replicating genes (as ribozymes) are considered. Dosage effect selects for optimal genomic composition within protocells that carries over to the genic composition of emerging chromosomes. Lacking an accurate segregation mechanism, protocells continue to benefit from the stochastic corrector principle (group selection of early replicators), but now at the chromosome level. A remarkable feature of this process is the appearance of multigene families (in optimal genic proportions) on chromosomes. An added benefit of chromosome formation is an increase in the selectively maintainable genome size (number of different genes), primarily due to the marked reduction of the assortment load. The establishment of chromosomes is under strong positive selection in protocells harboring unlinked genes. The error threshold of replication is raised to higher genome size by linkage due to the fact that deleterious mutations affecting protocells metabolism (hence fitness) show antagonistic (diminishing return) epistasis. This result strengthens the established benefit conferred by chromosomes on protocells allowing for the fixation of highly specific and efficient enzymes.
A dynamic model and an agent-based simulation model implementing the assumptions of the confrontational scavenging hypothesis on early protolanguage as an adaptive response of Homo erectus to gradual change in their habitat has been developed and studied. The core assumptions of the hypothesis and the model scenario are the pre-adaptation of our ancestors to occupy the ecological niche that they constructed for themselves by having evolved displaced communication and a rudimentary tool manufacture, two features allowing them to use a new, concentrated and abundant resource—megafauna carrion—on the savannahs replacing arboreal habitats owing to the drying climate of East Africa at about 2 Ma. The shift in diet required coordinated cooperation by the hominin scavengers confronted with concurrent predators. Power scavenging compelled displaced symbolic communication featuring a limited semantic range; syntax was not yet required. We show that phenotypic evolution on the accuracy of information transfer between cooperating hominins is a necessary and sufficient condition for the population of agents to survive the diet shift. Both the individual and the group fitness of the hominin horde increased with the accuracy of their protolanguage, with decreasing time allocated to foraging and thus more time left for culture. This article is part of the theme issue ‘Human socio-cultural evolution in light of evolutionary transitions’.
We propose a compact head-worn 3D display which provides glasses-free full motion parallax. Two picoprojectors placed on the viewer's head project images on a retro-reflective screen that reflects left and right images to the appropriate eyes of the viewer. The properties of different retro-reflective screen materials have been investigated, and the key parameters of the projection - brightness and cross-talk - have been calculated. A demonstration system comprising two projectors, a screen tracking system and a commercial retro-reflective screen has been developed to test the visual quality of the proposed approach.
Background Our aim is to determine the relationships among patient demographics, patient history, surgical experience, and conversion rate (CR) during elective laparoscopic cholecystectomies (LCs). Methods We analyzed data from patients who underwent LC surgery between 2005 and 2014 based on patient charts and electronic documentation. CR (%) was evaluated in 4013 patients who underwent elective LC surgery. The relationships between certain predictive factors (patient demographics, endoscopic retrograde cholangiopancreatography (ERCP), acute cholecystitis (AC), abdominal surgery in the patient history, as well as surgical experience) and CR were examined by univariate analysis and logistic regression. Results In our sample (N = 4013), the CR was 4.2%. The CR was twice as frequent among males than among females (6.8 vs. 3.2%, p < 0.001), and the chance of conversion increased from 3.4 to 5.9% in patients older than 65 years. The detected CR was 8.8% in a group of patients who underwent previous ERCP (8.8 vs. 3.5%, p < 0.001). From the ERCP indications, most often, conversion was performed because of severe biliary tract obstruction (CR: 9.3%). LC had to be converted to open surgery after upper and lower abdominal surgeries in 18.8 and 4.8% cases, respectively. Both AC and ERCP in the patient history raised the CR (12.3%, p < 0.001 and 8.8%, p < 0.001). More surgical experience and high surgery volume were not associated with a lower CR prevalence. Conclusions Patient demographics (male gender and age > 65 years), previous ERCP, and upper abdominal surgery or history of AC affected the likelihood of conversion. More surgical experience and high surgery volume were not associated with a lower CR prevalence.
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