Interpreting the dependence of mutation rates on age and time

Mutations can arise from the chance misincorporation of nucleotides during DNA replication or from DNA lesions that are not repaired correctly. We introduce a model that relates the source of mutations to their accumulation with cell divisions, providing a framework for understanding how mutation rates depend on sex, age and absolute time. We show that the accrual of mutations should track cell divisions not only when mutations are replicative in origin but also when they are non-replicative and repaired efficiently. One implication is that the higher incidence of cancer in rapidly renewing tissues, an observation ascribed to replication errors, could instead reflect exogenous or endogenous mutagens. We further find that only mutations that arise from inefficiently repaired lesions will accrue according to absolute time; thus, in the absence of selection on mutation rates, the phylogenetic "molecular clock" should not be expected to run steadily across species.Comment: 5 figures, 2 table

Peaceful transitions of power have been rare in modern states, but once the habit has been acquired it sticks

What incentives are there for non-democratic governments to agree to risk losing power in elections? Based on an analysis of over 3,000 elections which have taken place across the world since 1788, Adam Przeworski writes that the practice of peacefully changing governments via the ballot box has been a relatively rare occurrence in modern history. Nevertheless, he notes that while it is difficult to establish the first peaceful transition of power in a state, once the principle has been implemented it often becomes entrenched over time

The Political Economy of Redistribution under Democracy

We ask what redistributions of income and assets are feasible in a democracy, given the initial assets and their distribution. The question is motivated by the possibility that if redistribution is insufficient for the poor or excessive for the rich, they may turn against democracy. In turn, if no redistribution simultaneously satisfies the poor and the wealthy, democracy cannot be sustained. Hence, the corollary question concerns the conditions under which democracy is sustainable. Since decisions to save are endogenous, we solve explicitly for the current growth rates given any time path of future tax rates. We find that the optimal path of redistribution chosen by the median voter under the constraint of rebellion by the poor or the wealthy consists of redistributing as much as possible as soon as possible. However, this path is time inconsistent unless voters punish governments that deviate from their promises. Democracies survive in wealthy societies, with a lower average capital stock when they are more equal.Sustainable Democracy, Optimal Taxes

Dehn surgery, homology and hyperbolic volume

If a closed, orientable hyperbolic 3--manifold M has volume at most 1.22 then H_1(M;Z_p) has dimension at most 2 for every prime p not 2 or 7, and H_1(M;Z_2) and H_1(M;Z_7) have dimension at most 3. The proof combines several deep results about hyperbolic 3--manifolds. The strategy is to compare the volume of a tube about a shortest closed geodesic C in M with the volumes of tubes about short closed geodesics in a sequence of hyperbolic manifolds obtained from M by Dehn surgeries on C.Comment: This is the version published by Algebraic & Geometric Topology on 8 December 200

O umijeću pisanja projektnih prijedloga

Prijevod s engleskog: Silva Mežnarić (Studeni 1994.

Variation in the molecular clock of primates

Events in primate evolution are often dated by assuming a constant rate of substitution per unit time, but the validity of this assumption remains unclear. Among mammals, it is well known that there exists substantial variation in yearly substitution rates. Such variation is to be expected from differences in life history traits, suggesting it should also be found among primates. Motivated by these considerations, we analyze whole genomes from 10 primate species, including Old World Monkeys (OWMs), New World Monkeys (NWMs), and apes, focusing on putatively neutral autosomal sites and controlling for possible effects of biased gene conversion and methylation at CpG sites. We find that substitution rates are up to 64% higher in lineages leading from the hominoid–NWM ancestor to NWMs than to apes. Within apes, rates are ∼2% higher in chimpanzees and ∼7% higher in the gorilla than in humans. Substitution types subject to biased gene conversion show no more variation among species than those not subject to it. Not all mutation types behave similarly, however; in particular, transitions at CpG sites exhibit a more clocklike behavior than do other types, presumably because of their nonreplicative origin. Thus, not only the total rate, but also the mutational spectrum, varies among primates. This finding suggests that events in primate evolution are most reliably dated using CpG transitions. Taking this approach, we estimate the human and chimpanzee divergence time is 12.1 million years,​ and the human and gorilla divergence time is 15.1 million years​.United States. National Institutes of Health (F32 GM115006-01

Genetic Structure of Chimpanzee Populations

Little is known about the history and population structure of our closest living relatives, the chimpanzees, in part because of an extremely poor fossil record. To address this, we report the largest genetic study of the chimpanzees to date, examining 310 microsatellites in 84 common chimpanzees and bonobos. We infer three common chimpanzee populations, which correspond to the previously defined labels of “western,” “central,” and “eastern,” and find little evidence of gene flow between them. There is tentative evidence for structure within western chimpanzees, but we do not detect distinct additional populations. The data also provide historical insights, demonstrating that the western chimpanzee population diverged first, and that the eastern and central populations are more closely related in time

Reevaluating the modernization hypothesis

We revisit and critically reevaluate the widely accepted modernization hypothesis which claims that per capita income causes the creation and the consolidation of democracy. Existing studies find support for this hypothesis because they fail to control for the presence of omitted variables. Controlling for these factors either by including country fixed effects in a linear model or by including parameterized random effects in a nonlinear double hazard model removes the correlation between income and the likelihood of transitions to and from democratic regimes. In addition, the estimated fixed effects from the linear model are related to historical factors that affect both the level of income per capita and the likelihood of democracy in a country. This evidence is consistent with the idea that events during critical historical junctures can lead to divergent political–economic development paths, some leading to prosperity and democracy, others to relative poverty and non-democracy

Systole et rayon maximal des vari\'et\'es hyperboliques non compactes

We bound two global invariants of cusped hyperbolic manifolds: the length of the shortest closed geodesic (the systole), and the radius of the biggest embedded ball (the inradius). We give an upper bound for the systole, expressed in terms of the dimension and simplicial volume. We find a positive lower bound on the inradius independent of the dimension. These bounds are sharp in dimension 3, realized by the Gieseking manifold. It provides a new characterization of this manifold.Comment: 26 pages, 15 figure