Different evolutionary paths to complexity for small and large populations of digital organisms

A major aim of evolutionary biology is to explain the respective roles of adaptive versus non-adaptive changes in the evolution of complexity. While selection is certainly responsible for the spread and maintenance of complex phenotypes, this does not automatically imply that strong selection enhances the chance for the emergence of novel traits, that is, the origination of complexity. Population size is one parameter that alters the relative importance of adaptive and non-adaptive processes: as population size decreases, selection weakens and genetic drift grows in importance. Because of this relationship, many theories invoke a role for population size in the evolution of complexity. Such theories are difficult to test empirically because of the time required for the evolution of complexity in biological populations. Here, we used digital experimental evolution to test whether large or small asexual populations tend to evolve greater complexity. We find that both small and large---but not intermediate-sized---populations are favored to evolve larger genomes, which provides the opportunity for subsequent increases in phenotypic complexity. However, small and large populations followed different evolutionary paths towards these novel traits. Small populations evolved larger genomes by fixing slightly deleterious insertions, while large populations fixed rare beneficial insertions that increased genome size. These results demonstrate that genetic drift can lead to the evolution of complexity in small populations and that purifying selection is not powerful enough to prevent the evolution of complexity in large populations.Comment: 22 pages, 5 figures, 7 Supporting Figures and 1 Supporting Tabl

“Leftist”, “Rightist” and Intermediate Decompositions of Poverty Variations with an Application to China from 1990 to 2003

This paper investigates the influence of invariance axioms in the decomposition of observed poverty variations into growth and inequality effects. After a complete and critical review of the invariance axioms suggested in the literature, we show that few information is needed for the ordering of the effects respectively obtained through scale, translation and intermediate invariance. Using Chinese data for the period 1990-2003, we find that some commonly observed results of the decomposition are contingent to the invariance axiom choices whilst other are robust to changes in ethical preferences.Poverty;inequality effect;growth effect;Decomposition;scale invariance;translationinvariance;intermediate invariance;China

“Leftist”, “Rightist” and Intermediate Decompositions of Poverty: Variations with an Application to China from 1990 to 2003

This paper investigates the influence of invariance axioms in the decomposition of observed poverty variations into growth and inequality effects. After a complete and critical review of the invariance axioms suggested in the literature, we show that few information is needed for the ordering of the effects respectively obtained through scale, translation and intermediate invariance. Using Chinese data for the period 1990-2003, we find that some commonly observed results of the decomposition are contingent to the invariance axiom choices whilst other are robust to changes in ethical preferences.Poverty, inequality effect, growth effect, decomposition, scale invariance, translation invariance, intermediate invariance, China.

“Leftist”, “Rightist” and Intermediate Decompositions of Poverty Variations with an Application to China from 1990 to 2003

This paper investigates the influence of invariance axioms in the decomposition of observed poverty variations into growth and inequality effects. After a complete and critical review of the invariance axioms suggested in the literature, we show that few information is needed for the ordering of the effects respectively obtained through scale, translation and intermediate invariance. Using Chinese data for the period 1990-2003, we find that some commonly observed results of the decomposition are contingent to the invariance axiom choices whilst other are robust to changes in ethical preferences.Poverty, inequality effect, growth effect, Decomposition, scale invariance, translationinvariance, intermediate invariance, China

Does self-replication imply evolvability?

The most prominent property of life on Earth is its ability to evolve. It is often taken for granted that self-replication--the characteristic that makes life possible--implies evolvability, but many examples such as the lack of evolvability in computer viruses seem to challenge this view. Is evolvability itself a property that needs to evolve, or is it automatically present within any chemistry that supports sequences that can evolve in principle? Here, we study evolvability in the digital life system Avida, where self-replicating sequences written by hand are used to seed evolutionary experiments. We use 170 self-replicators that we found in a search through 3 billion randomly generated sequences (at three different sequence lengths) to study the evolvability of generic rather than hand-designed self-replicators. We find that most can evolve but some are evolutionarily sterile. From this limited data set we are led to conclude that evolvability is a likely--but not a guaranteed-- property of random replicators in a digital chemistry.Comment: 8 pages, 5 figures. To appear in "Advances in Artificial Life": Proceedings of the 13th European Conference on Artificial Life (ECAL 2015

Evolvability tradeoffs in emergent digital replicators

The role of historical contingency in the origin of life is one of the great unknowns in modern science. Only one example of life exists--one that proceeded from a single self-replicating organism (or a set of replicating hyper-cycles) to the vast complexity we see today in Earth's biosphere. We know that emergent life has the potential to evolve great increases in complexity, but it is unknown if evolvability is automatic given any self-replicating organism. At the same time, it is difficult to test such questions in biochemical systems. Laboratory studies with RNA replicators have had some success with exploring the capacities of simple self-replicators, but these experiments are still limited in both capabilities and scope. Here, we use the digital evolution system Avida to explore the interaction between emergent replicators (rare randomly-assembled self-replicators) and evolvability. We find that we can classify fixed-length emergent replicators in Avida into two classes based on functional analysis. One class is more evolvable in the sense of optimizing their replication abilities. However, the other class is more evolvable in the sense of acquiring evolutionary innovations. We tie this trade-off in evolvability to the structure of the respective classes' replication machinery, and speculate on the relevance of these results to biochemical replicators.Comment: 26 pages, 5 figures. Revised version, title change

Intergenerational Mobility in China

In this paper, I study the intergenerational mobility of education and income in China. Using the CHNS database which gives information on parental educational attainment and income level, I show that there is a relatively high intergenerational mobility in China, compared to other developed and developing countries. Even if parents' social characteristics influence the child's ones, the transmission of parents' educational and income level remains low. Nevertheless, I stress a growing impact of parents' income on the determination of children educational attainment, what can be an increasing factor of income inequality in the future. Moreover, I emphasize that parents' farming activity plays an important and significant negative role in the child's educational level.cerdi

Origin of life in a digital microcosm

While all organisms on Earth descend from a common ancestor, there is no consensus on whether the origin of this ancestral self-replicator was a one-off event or whether it was only the final survivor of multiple origins. Here we use the digital evolution system Avida to study the origin of self-replicating computer programs. By using a computational system, we avoid many of the uncertainties inherent in any biochemical system of self-replicators (while running the risk of ignoring a fundamental aspect of biochemistry). We generated the exhaustive set of minimal-genome self-replicators and analyzed the network structure of this fitness landscape. We further examined the evolvability of these self-replicators and found that the evolvability of a self-replicator is dependent on its genomic architecture. We studied the differential ability of replicators to take over the population when competed against each other (akin to a primordial-soup model of biogenesis) and found that the probability of a self-replicator out-competing the others is not uniform. Instead, progenitor (most-recent common ancestor) genotypes are clustered in a small region of the replicator space. Our results demonstrate how computational systems can be used as test systems for hypotheses concerning the origin of life.Comment: 20 pages, 7 figures. To appear in special issue of Philosophical Transactions of the Royal Society A: Re-Conceptualizing the Origins of Life from a Physical Sciences Perspectiv

The short and long of it: neural correlates of temporal-order memory for autobiographical events

Previous functional neuroimaging studies of temporal-order memory have investigated memory for laboratory stimuli that are causally unrelated and poor in sensory detail. In contrast, the present functional magnetic resonance imaging (fMRI) study investigated temporal-order memory for autobiographical events that were causally interconnected and rich in sensory detail. Participants took photographs at many campus locations over a period of several hours, and the following day they were scanned while making temporal-order judgments to pairs of photographs from different locations. By manipulating the temporal lag between the two locations in each trial, we compared the neural correlates associated with reconstruction processes, which we hypothesized depended on recollection and contribute mainly to short lags, and distance processes, which we hypothesized to depend on familiarity and contribute mainly to longer lags. Consistent with our hypotheses, parametric fMRI analyses linked shorter lags to activations in regions previously associated with recollection (left prefrontal, parahippocampal, precuneus, and visual cortices), and longer lags with regions previously associated with familiarity (right prefrontal cortex). The hemispheric asymmetry in prefrontal cortex activity fits very well with evidence and theories regarding the contributions of the left versus right prefrontal cortex to memory (recollection vs. familiarity processes) and cognition (systematic vs. heuristic processes). In sum, using a novel photo-paradigm, this study provided the first evidence regarding the neural correlates of temporal-order for autobiographical events