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THE EXERCISE. “ For the electron, superpositions of states must be available in the observer's future at least until Tn when it disappears, in order for it to move forward in time to be measured at T2, T3..... What is the difference between these two situations?” https://lnkd.in/gDaxUYAS View in LinkedIn

THE EXERCISE. “At some times T2, T3..... the physicist makes measurements and finds the two particles. For the antiparticle, moving backwards in time, superpositions of states must be available in the observer's future where it will exist at least until Tn when it appears, in order for it to move backward in time to be measured at ......T3, T2.” https://lnkd.in/gDaxUYAS View in LinkedIn

A veritable blaze of Montpellier maples planted along the upper path leading to Girona’s Sant Daniel valley. View in LinkedIn

THE CAMBRIDGE PHILOSOPHICAL SOCIETY. “Adam Sedgwick (1785–1873) and John Stevens Henslow (1796–1861). Both men were aware that the study of the sciences in their University was largely moribund. Although there were professors of both botany and geology at Cambridge, and post-Newtonian mathematics was flourishing, the sciences...were a “peripheral activity”. The purpose of the University was primarily as a training ground for clerics.” https://lnkd.in/gkn3BKFd View in LinkedIn

HITCHHIKING MUTATIONS. “Indeed, both mutation-rate scenarios have been observed in an E. coli population in the LTEE. After thousands of generations, a mutation in the nucleoside triphosphate pyrophosphohydrolase gene (mutT) that caused a ~150-fold increase in mutation rates spread through the population, presumably by hitchhiking with one or more beneficial mutations.” https://www.nature.com/articles/nrg3564 View in LinkedIn

RISKY STRATEGY. “In the long term, increased mutation rates are not without evolutionary risk. Opportunities for mutations that greatly improve fitness will eventually run out in the optimization regime. It may then be beneficial to compensate for a hypermutator defect and to become less evolvable in order to lower the genetic load.” https://www.nature.com/articles/nrg3564 View in LinkedIn

POSITIVE IMPACT. “However, the hypermutator subpopulation has increased evolvability because it has a much higher per-capita chance of producing the next highly beneficial mutation, or multiple beneficial mutations, than a non-mutator competitor (Fig. 3a). Thus, despite their slight fitness costs, hypermutators can sometimes hitchhike to fixation with the beneficial mutations that they generate.” https://www.nature.com/articles/nrg3564 View in LinkedIn

FREQUENCY. “Given the balance between their high rate of occurrence and small fitness costs, hypermutators might exist at frequencies of 10(-6) -10(-4) in experimental populations of E. coli.” https://www.nature.com/articles/nrg3564 View in LinkedIn

ORIGIN. “However, the initial spontaneous mutation rate is typically low, as discussed above, so that the fitness cost of producing mutations at even a 100-fold higher rate is small. Furthermore, new hypermutator variants frequently arise because loss-of-function mutations in many genes give rise to this phenotype.” https://www.nature.com/articles/nrg3564 View in LinkedIn

FRAGMENT FROM NATURE continues from last weekend and ends this weekend on the theme of the very heart of evolution, inheritance with variation, or random gene mutation. The other face of evolution, natural selection, is performed by differential death and survival. Generate diversity, select and repeat. Generate diversity, select and repeat. This is evolution at its core. View in LinkedIn