The concept of fitness has long been a topic of intense debate among evolutionary biologists and their critics, with its definition and explanatory power coming under attack. In this book, Richard ...Michod offers a fresh, dynamical interpretation of evolution and fitness concepts. He argues that evolution has no enduring products; what matters is the process of genetic change. Whereas many biologists have focused on competition and aggression as determining factors in survival, Michod, by concentrating on the emergence of individuality at new and more complex levels, finds that cooperation plays even a greater role. Michod first considers the principles behind the hierarchically nested levels of organization that constitute life: genes, chromosomes, genomes, cells, multicellular organisms, and societies. By examining the evolutionary transitions from the molecular level up to the whole organism, the author explains how cooperation and conflict in a multilevel setting leads to new levels of fitness. He builds a model of fitness drawing on recent developments in ecology and multilevel selection theory and on new explanations of the origin of life. Michod concludes with a discussion of the philosophical implications of his theory of fitness, a theory that addresses the most fundamental and unique concept in all of biology.
The use of regression analysis has been instrumental in allowing evolutionary biologists to estimate the strength and mode of natural selection. Although directional and correlational selection ...gradients are equal to their corresponding regression coefficients, quadratic regression coefficients must be doubled to estimate stabilizing/disruptive selection gradients. Based on a sample of 33 papers published in Evolution between 2002 and 2007, at least 78% of papers have not doubled quadratic regression coefficients, leading to an appreciable underestimate of the strength of stabilizing and disruptive selection. Proper treatment of quadratic regression coefficients is necessary for estimation of fitness surfaces and contour plots, canonical analysis of the γ matrix, and modeling the evolution of populations on an adaptive landscape.
Despite the potential for rapid evolution, stasis is commonly observed over geological timescales—the so-called "paradox of stasis." This paradox would be resolved if stabilizing selection were ...common, but stabilizing selection is infrequently detected in natural populations. We hypothesize a simple solution to this apparent disconnect: stabilizing selection is hard to detect empirically once populations have adapted to a fitness peak. To test this hypothesis, we developed an individual-based model of a population evolving under an invariant stabilizing fitness function. Stabilizing selection on the population was infrequently detected in an "empirical" sampling protocol, because (1) trait variation was low relative to the fitness peak breadth; (2) nonselective deaths masked selection; (3) populations wandered around the fitness peak; and (4) sample sizes were typically too small. Moreover, the addition of negative frequency-dependent selection further hindered detection by flattening or even dimpling the fitness peak, a phenomenon we term "squashed stabilizing selection." Our model demonstrates that stabilizing selection provides a plausible resolution to the paradox of stasis despite its infrequent detection in nature. The key reason is that selection "erases its traces": once populations have adapted to a fitness peak, they are no longer expected to exhibit detectable stabilizing selection.
We propose MC+, a fast, continuous, nearly unbiased and accurate method of penalized variable selection in high-dimensional linear regression. The LASSO is fast and continuous, but biased. The bias ...of the LASSO may prevent consistent variable selection. Subset selection is unbiased but computationally costly. The MC+ has two elements: a minimax concave penalty (MCP) and a penalized linear unbiased selection (PLUS) algorithm. The MCP provides the convexity of the penalized loss in sparse regions to the greatest extent given certain thresholds for variable selection and unbiasedness. The PLUS computes multiple exact local minimizers of a possibly nonconvex penalized loss function in a certain main branch of the graph of critical points of the penalized loss. Its output is a continuous piecewise linear path encompassing from the origin for infinite penalty to a least squares solution for zero penalty. We prove that at a universal penalty level, the MC+ has high probability of matching the signs of the unknowns, and thus correct selection, without assuming the strong irrepresentable condition required by the LASSO. This selection consistency applies to the case of p ≫ n, and is proved to hold for exactly the MC+ solution among possibly many local minimizers. We prove that the MC+ attains certain minimax convergence rates in probability for the estimation of regression coefficients in l r balls. We use the SURE method to derive degrees of freedom and C p -type risk estimates for general penalized LSE, including the LASSO and MC+ estimators, and prove their unbiasedness. Based on the estimated degrees of freedom, we propose an estimator of the noise level for proper choice of the penalty level. For full rank designs and general sub-quadratic penalties, we provide necessary and sufficient conditions for the continuity of the penalized LSE. Simulation results overwhelmingly support our claim of superior variable selection properties and demonstrate the computational efficiency of the proposed method.
Summary
Natural selection shapes genome‐wide patterns of diversity within species and divergence between species. However, quantifying the efficacy of selection and elucidating the relative ...importance of different types of selection in shaping genomic variation remain challenging.
We sequenced whole genomes of 101 individuals of three closely related oak species to track the divergence history, and to dissect the impacts of selective sweeps and background selection on patterns of genomic variation.
We estimated that the three species diverged around the late Neogene and experienced a bottleneck during the Pleistocene. We detected genomic regions with elevated relative differentiation (‘FST‐islands’). Population genetic inferences from the site frequency spectrum and ancestral recombination graph indicated that FST‐islands were formed by selective sweeps. We also found extensive positive selection; the fixation of adaptive mutations and reduction neutral diversity around substitutions generated a signature of selective sweeps. Prevalent negative selection and background selection have reduced genetic diversity in both genic and intergenic regions, and contributed substantially to the baseline variation in genetic diversity.
Our results demonstrate the importance of linked selection in shaping genomic variation, and illustrate how the extent and strength of different selection models vary across the genome.
With the advances in innovative instrumentation and various valuable applications, near-infrared (NIR) spectroscopy has become a mature analytical technique in various fields. Variable (wavelength) ...selection is a critical step in multivariate calibration of NIR spectra, which can improve the prediction performance, make the calibration reliable and provide simpler interpretation. During the last several decades, there have been a large number of variable selection methods proposed in NIR spectroscopy. In this paper, we generalize variable selection methods in a simple manner to introduce their classifications, merits and drawbacks, to provide a better understanding of their characteristics, similarities and differences. We also introduce some hybrid and modified methods, highlighting their improvements. Finally, we summarize the limitations of existing variable selection methods, providing our remarks and suggestions on the development of variable selection methods, to promote the development of NIR spectroscopy.
•Generalize variable selection methods in a simple manner to provide a better understanding of their characteristics.•Introduce their modified and hybrid methods and highlighting their improvements.•Summarize the limitations and mention seven aspects of the problem affecting the existing variable selection methods.•Provide our remarks and suggestions on the trends of the development on the variable selection methods in NIR spectra.
The complex and ever-changing nature of today's—and tomorrow's—workforce demands that all involved in talent management rethink how to attract, engage, and grow future talent. This forward-looking ...handbook captures talent management's evolution from a series of transactions to a fluid process that includes talent development. With 20-plus chapters written by more than 30 contributors, the ATD Talent Management Handbook challenges you to think about the talent model of the future through the lens of different workforce models. It offers progressive thoughts on the current state of talent management and on how the function needs to adapt. Leaders, practitioners, and consultants alike will find useful insights and answers to relevant talent management challenges. Edited by learning and development authority Terry Bickham, this handbook covers the entire talent management cycle, from talent acquisition and engagement to leadership development and succession planning. ATD's first handbook on talent management, this book includes a foreword by ATD President and CEO Tony Bingham, highlighting the foundational components of talent development and its role within talent management.
Over the arc of his career, E. O. Wilson first embraced, then popularized, and finally rejected an extreme genetical hereditarian view of human nature. The controversy that ensued during the period ...of popularization (largely in the 1970s and 1980s) obscured the fact that empirical and theoretical research during this time undercut the assumptions necessary for this view. By the end of his career, Wilson accepted the fact that individual/kin selection models were insufficient to explain human behavior and society, and he began conducting research based upon multilevel (group) selection, an idea he had previously scorned.
PDF
