posted 21. September 2003 00:35                   

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Abstract

We describe the evolution of macromolecules as an information transmission process and apply tools from Shannon information theory to it. This allows us to isolate three independent, competing selective pressures that we term compression, transmission, and neutrality selection. The first two affect genome length: the pressure to conserve resources by compressing the code, and the pressure to acquire additional information that improves the channel, increasing the rate of information transmission into each offspring.
Noisy transmission channels (replication with mutations) give rise to a third pressure that acts on the actual encoding of information; it maximizes the fraction of mutations that are neutral with respect to the phenotype. This neutrality selection has important implications for the evolution of evolvability. We demonstrate each selective pressure in experiments with digital organisms.

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This implies that a population can minimize its mutational load by increasing the probability that a mutation is neutral, or, equivalently, decreasing the probability that a mutation is deleterious. Experiments with digital organisms
confirm this view. In particular, an analysis of an
aggregate of approximately 10 million generations of the evolution of digital organisms has never revealed a single case in which the effective fitness, Eq. (3), has decreased. The selection of neutrality has a number of interesting consequences when translated to population biology. First, it might provide a convincing mechanism to explain the actual amount of neutrality in the genomes of higher organisms. Furthermore, because a higher neutrality implies both larger fitness variations and the potential for more information acquisition, neutrality selection implies a selective pressure for the evolution of evolvability (see, e.g. Wagner and enberg, 1996; Gerhart and Kirschner, 1997; and ncel and Fontana, 2000) that is molecular at its origin, and provides added support for the idea that robustness is actively selected for in the evolution of development (Gibson and Wagner, 2000). That it may also have left traces in the
genomes of higher organisms in the form of proteins that confer neutrality to other proteins (Rutherford and Lindquist, 1998; Wagner et al., 1999; Queitsch et al., 2002) is a tantalizing suggestion that awaits confirmation.

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Abstract. – Robustness is the invariance of phenotypes in the face of perturbation. The robustness of phenotypes appears at various levels of biological organization, including gene expression, protein folding, metabolic flux, physiological homeostasis, development, and even organismal fitness. The mechanisms underlying robustness are diverse, ranging from thermodynamic stability at the RNA and protein level to behavior at the organismal level. Robustness can be directed toward either heritable perturbations (e.g. mutations) or non heritable perturbations (e.g. the weather). Here we focus on the first kind of robustness – genetic robustness – and survey three growing avenues of research: (1) measuring genetic robustness in nature, (2) understanding the evolution of genetic robustness, and (3) exploring the implications of genetic robustness on future evolution.

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posted 21. September 2003 14:49                   

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Progress has become a suspect concept in evolutionary biology, not the least because the core concepts of neo-Darwinism do not support the idea that evolution is progressive. There have been a number of attempts to account for directionality in evolution through additions to the core hypotheses of neo-Darwinism, but they do not establish progressiveness, and they are somewhat of an ad hoc collection. The standard account of fitness and adaptation can be rephrased in terms of information theory. From this, an information of adaptation can be defined in terms of a fitness function. The information of adaptation is a measure of the mutual information between biota and their environment. If the actual state of adaptation lags behind the state of optimal adaptation, then it is possible for the information of adaptation to increase indefinitely. Since adaptations are functional, this suggests the possibility of progressive evolution in the sense of increasing adaptation.

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