The evolutionary origins of modularity

A central biological question is how natural organisms are so evolvable (capable of quickly adapting to new environments). A key driver of evolvability is the widespread modularity of biological networks—their organization as functional, sparsely connected subunits—but there is no consensus regarding why modularity itself evolved. Although most hypotheses assume indirect selection for evolvability, here we demonstrate that the ubiquitous, direct selection pressure to reduce the cost of connections between network nodes causes the emergence of modular networks. Computational evolution experiments with selection pressures to maximize network performance and minimize connection costs yield networks that are significantly more modular and more evolvable than control experiments that only select for performance. These results will catalyse research in numerous disciplines, such as neuroscience and genetics, and enhance our ability to harness evolution for engineering purposes.     

The conservation and evolutionary modularity of metabolism

Background  

Cellular metabolism is a fundamental biological system consisting of myriads of enzymatic reactions that together fulfill the basic requirements of life. The recent availability of vast amounts of sequence data from diverse sets of organisms provides an opportunity to systematically examine metabolism from a comparative perspective. Here we supplement existing genome and protein resources with partial genome datasets derived from 193 eukaryotes to present a comprehensive survey of the conservation of metabolism across 26 taxa representing the three domains of life.     

The evolutionary value of recombination is constrained by genome modularity

Genetic recombination is a fundamental evolutionary mechanism promoting biological adaptation. Using engineered recombinants of the small single-stranded DNA plant virus, Maize streak virus (MSV), we experimentally demonstrate that fragments of genetic material only function optimally if they reside within genomes similar to those in which they evolved. The degree of similarity necessary for optimal functionality is correlated with the complexity of intragenomic interaction networks within which genome fragments must function. There is a striking correlation between our experimental results and the types of MSV recombinants that are detectable in nature, indicating that obligatory maintenance of intragenome interaction networks strongly constrains the evolutionary value of recombination for this virus and probably for genomes in general.     

Mechanisms of madness: evolutionary psychiatry without evolutionary psychology

Delusions are currently characterised as false beliefs produced by incorrect inference about external reality (DSM IV). This inferential conception has proved hard to link to explanations pitched at the level of neurobiology and neuroanatomy. This paper provides that link via a neurocomputational theory, based on evolutionary considerations, of the role of the prefrontal cortex in regulating offline cognition. When pathologically neuromodulated the prefrontal cortex produces hypersalient experiences which monopolise offline cognition. The result is characteristic psychotic experiences and patterns of thought. This bottom-up account uses neural network theory to integrate recent theories of the role of dopamine in delusion with the insights of inferential accounts. It also provides a general model for evolutionary psychiatry which avoids theoretical problems imported from evolutionary psychology.     

The evolutionary psychology of women's aggression

Evolutionary researchers have identified age, operational sex ratio and high variance in male resources as factors that intensify female competition. These are discussed in relation to escalated intrasexual competition for men and their resources between young women in deprived neighbourhoods. For these women, fighting is not seen as antithetical to cultural conceptions of femininity, and female weakness is disparaged. Nonetheless, even where competitive pressures are high, young women''s aggression is less injurious and frequent than young men''s. From an evolutionary perspective, I argue that the intensity of female aggression is constrained by the greater centrality of mothers, rather than fathers, to offspring survival. This selection pressure is realized psychologically through a lower threshold for fear among women. Neuropsychological evidence is not yet conclusive but suggests that women show heightened amygdala reactivity to threatening stimuli, may be better able to exert prefrontal cortical control over emotional behaviour and may consciously register fear more strongly via anterior cingulate activity. The impact of testosterone and oxytocin on the neural circuitry of emotion is also considered.     

The cognitive and evolutionary psychology of religion

The following reviews recent developments in the cognitive and evolutionary psychology of religion, and argues for an adaptationist stance.     

The evolutionary psychology of mate selection in Morocco

Patterns of mate preference in Morocco are investigated in order to test whether they support hypotheses advanced by David Buss and other evolutionary psychologists. Because of the custom of cousin marriage in Morocco, a multivariate model that included cosocialization data was developed for the purpose of testing the Westermarck hypothesis of inbreeding avoidance. Hence, two previously separate domains of research are unified in one design that permits the further exploration of questions pertaining to the domain specificity of psychological mechanisms. Multiple independent mate choice predictors were identified using logistic regression analysis. Results support the Westermarck hypothesis of inbreeding avoidance. Sleeping in the same room during childhood was found in both sexes to produce an aversion to marriage. Other evidence suggests that aversion to inbreeding extends further among females than males in that females but not males show an aversion to marriage to related individuals with whom they had daily social contact in early childhood. The evolutionary prediction that females differ from males concerning resource holding capacity was also supported. Females showed a preference for males whom they judged to have higher social status than theirs, while this criterion was unimportant for males. The predicted sex difference in preferred age of marriage partner was also supported. Contrary to previous findings, the predicted difference between the sexes with regard to physical attractiveness was not supported. This research was supported by NSF grant BSN 90-19876. Alex Walter obtained a Ph.D. in anthropology from Rutgers University in 1992. He was a research associate at Rutgers from 1994 to 1995. He has taught at Cornell College and at Rutgers and Princeton universities. He is currently working on additional articles that will present data from his dissertation research on mate selection and inbreeding avoidance in Morocco.     

Developmental modularity and the evolutionary diversification of arthropod limbs

Segmentation is one of the most salient characteristics of arthropods, and differentiation of segments along the body axis is the basis of arthropod diversification. This article evaluates whether the evolution of segmentation involves the differentiation of already independent units, i.e., do segments evolve as modules? Because arthropod segmental differentiation is commonly equated with differential character of appendages, we analyze appendages by comparing similarities and differences in their development. The comparison of arthropod limbs, even between species, is a comparison of serially repeated structures. Arthropod limbs are not only reiterated along the body axis, but limbs themselves can be viewed as being composed of reiterated parts. The interpretation of such reiterated structures from an evolutionary viewpoint is far from obvious. One common view is that serial repetition is evidence of a modular organization, i.e., repeated structures with a common fundamental identity that develop semi-autonomously and are free to diversify independently. In this article, we evaluate arthropod limbs from a developmental perspective and ask: are all arthropod limbs patterned using a similar set of mechanisms which would reflect that they all share a generic coordinate patterning system? Using Drosophila as a basis for comparison, we find that appendage primordia, positioned along the body using segmental patterning coordinates, do indeed have elements of common identity. However, we do not find evidence of a single coordinate system shared either between limbs or among limb branches. Data concerning the other diagnostic of developmental modularity--semi-autonomy of development--are not currently available for sufficient taxa. Nonetheless, some data comparing patterns of morphogenesis provide evidence that limbs cannot always be temporally or spatially decoupled from the development of their neighbors, suggesting that segment modularity is a derived character.     

The evolutionary psychology of obsessive-compulsive disorder: the role of cognitive metarepresentation

Repetitive unpleasant thoughts and ritualized behaviors are the key features of obsessive-compulsive disorder (OCD). The classical neuroethological models of OCD rely largely on behavioral similarities between animal stereotypies and human compulsive rituals and are unable to account for the cognitive component of OCD. The cognitive symptoms of OCD need to be addressed in an evolutionary psychological context that incorporates information about human brain evolution. OCD can be understood as an extreme on a continuum of evolved harm-avoidance strategies. A pathological exaggeration of our evolved capacity to cognitively represent future scenarios, including imagined consequences of our own thoughts and actions (metarepresentation), may be part of the set of evolved psychological mechanisms contributing to the psychopathology of OCD. The costly side of the adaptive ability to anticipate future needs or threats could be that etiologically heterogeneous affections of the underlying striatal-frontal brain circuits may render an individual vulnerable to develop OCD.     

The evolutionary significance of mass extinctions

Local extinctions of populations, species or groups of species in a particular area are commonly observed by biologists. There are also historical records of the total extinction of single species such as the Dodo, the Great Auk and the Tasmanian Wolf. Mass extinctions are on a much larger scale, and their study is based on the fossil record. The aims of this review are to explore the nature of mass extinctions and their evolutionary significance. The key questions are: what is mass extinction, what are the causes of mass extinctions, do mass extinctions follow a regular pattern, and how do mass extinctions affect our understanding of evolutionary processes?     

Testing the vulnerability of the phylotypic stage: on modularity and evolutionary conservation

The phylotypic stage is the developmental stage at which vertebrates most resemble each other. In this study we test the plausibility of the hypotheses of Sander [1983, Development and Evolution, Cambridge University Press] and Raff [1994, Early Life on Earth, Columbia University Press; 1996, The Shape of Life, University of Chicago Press] that the phylotypic stage is conserved due to the intense and global interactivity occurring during that stage. First, we test the prediction that the phylotypic stage is much more vulnerable than any other stage. A search of the teratological literature shows that disturbances at this stage lead to a much higher mortality than in other stages, in accordance with the prediction. Second, we test whether that vulnerability is indeed caused by the interactiveness and lack of modularity of the inductions or, alternatively, is caused by some particularly vulnerable process going on at that time. From the pattern of multiple induced anomalies we conclude that it is indeed the interactiveness that is the root cause of the vulnerability. Together these results support the hypotheses of Sander and Raff. We end by presenting an argument on why the absence of modularity in the inductive interactions may also be the root cause of the conservation of the much discussed temporal and spatial colinearity of the Hox genes. J. Exp. Zool. (Mol. Dev. Evol.) 291:195-204, 2001.     

Toward an evolutionary psychology of religiosity

How can the evolution of religiosity be explained? To answer this question, we attempt to develop an understanding of the psychological domains underlying religious behaviour. We see four evolved domains, the sum and interaction of which constitute religiosity, namely: mysticism, ethics, myths and rituals. Even if the individual content, accents and implementations differ in each specific religion, they nevertheless derive from evolved Darwinian algorithms that are species-specific adaptations of homo sapiens. Mysticism. Intuitive ontologies are the basis for mystical experiences. Usually they serve to classify reality into animate and inanimate objects, animals or plants, for example. For a variety of psychological reasons, supernatural experiences result from a mixture of different ontological categories. Ethics. The basis for ethics lies in the social competency of human beings. Ethics is founded on the concept of social exchange ("social-contract algorithm") with its ideas about reciprocity, fairness, justice, cheater detection, in-group/out-group differentiation, etc. Myths. The basis for myths is the "language instinct". We interpret myths as the verbal expression of the cognitive content of those individual modules that constitute the belief system. Above all, myths document the experience and processing of contingency and thus help social bonding. Rituals. Rituals are based on the handicap principle. By making certain symbols and acts more expensive, they signal commitment for a reliable in-group morale. In conclusion, we argue that human religiosity emerges from a cognitive interaction between these four domains. Religiosity processes contingencies and enhances co-operation through social bonding, norm setting and cheater detection. It fulfils those functions for which the mental modules of its four domains have evolved so that we feel it appears to be justified to attribute to religiosity the evolutionary status of an adaptation.     

Adaptation: "a critique of some current evolutionary thought"

In his classic Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought (1966), George Williams showed definitively that our understanding of adaptation, a central concept of evolutionary theory, must be gene-centered. The purpose of adaptations is to further the replication of genes. Genes are machines for turning out more genes; and adaptations are the means by which genes pluck resources from the world to promote this self-replication. Thus adaptations transform potential resources from part of the indifferent world-at-large into tailor-made environments, environments brimming with resources for organisms' distinctive adaptive needs. Systematically dif ferent adaptive problems therefore give rise to different environments; and so different species, for example, have different environments. Thus a gene-centered analysis of adaptations implies a gene-centered theory of environments. Without genes to specify what constitutes an environment, environments would not exist. Rather than being separate from biology, an autonomous, independent force, environments are themselves the products of biology. So a gene-centered view, far from depreciating the environment, furnishes a rich and precise understanding of its importance.     

An evolutionary critique of cultural analysis in sociology

A noteworthy development that has transpired in American sociology in the past quarter century has been the increasingly sophisticated interest in the analysis of human cultural systems. Sadly, however, these analyses reveal that social scientists rarely appreciate the profoundly evolutionary aspects of human culture. The chief purpose of this essay is to address this shortcoming and to offer some tentative suggestions toward its rectification. The essay begins by briefly reviewing recent developments in the analysis of cultural systems, primarily by reference to the influential work of Wuthnow. Second, a common flaw in these approaches is addressed—namely, the absence of any recognition of the value of grounding sociocultural theory in an informed evolutionary framework—and the case is made that this shortcoming is avoidable, even within the context of the intellectual traditions of the social sciences. Third, the evolutionary foundations of human cultural behavior are explored in terms of an analysis of relevant theoretical and empirical developments in the evolutionary neurosciences. Fourth, the value of these insights is illustrated by reference to an evolutionary critique of a recent and thought-provoking contribution to the study of modern political culture—Douglas and Wildavsky’s analysis ofRisk and Culture. Finally, the article concludes by emphasizing the value of and the necessity for incorporating evolutionary reasoning into the domain of sociocultural theory.     

Darwin in mind: new opportunities for evolutionary psychology

Evolutionary Psychology (EP) views the human mind as organized into many modules, each underpinned by psychological adaptations designed to solve problems faced by our Pleistocene ancestors. We argue that the key tenets of the established EP paradigm require modification in the light of recent findings from a number of disciplines, including human genetics, evolutionary biology, cognitive neuroscience, developmental psychology, and paleoecology. For instance, many human genes have been subject to recent selective sweeps; humans play an active, constructive role in co-directing their own development and evolution; and experimental evidence often favours a general process, rather than a modular account, of cognition. A redefined EP could use the theoretical insights of modern evolutionary biology as a rich source of hypotheses concerning the human mind, and could exploit novel methods from a variety of adjacent research fields.     

Beyond hairballs: The use of quantitative mass spectrometry data to understand protein-protein interactions

The past 10years have witnessed a dramatic proliferation in the availability of protein interaction data. However, for interaction mapping based on affinity purification coupled with mass spectrometry (AP-MS), there is a wealth of information present in the datasets that often goes unrecorded in public repositories, and as such remains largely unexplored. Further, how this type of data is represented and used by bioinformaticians has not been well established. Here, we point out some common mistakes in how AP-MS data are handled, and describe how protein complex organization and interaction dynamics can be inferred using quantitative AP-MS approaches.