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This chapter examines the developmental mechanisms underlying evolutionary novelties. It first considers the role of the environment in evolutionary innovations, with particular emphasis on how environmental perturbations result in the release of cryptic genetic variation. It then explores where the positional information for novel characters comes from before explaining derived mechanical stimuli and the origin of novelties in the avian hind limb skeleton. It also discusses the origin of character identity networks and the evolution of novel signaling centers, focusing on two novel morphological characters: the butterfly eyespot and the turtle carapace. Finally, it reflects on the developmental biology of novelties, emphasizing the complex and multifaceted nature of the evolutionary changes in the developmental mechanisms that contribute to the origin of novel body parts.

This chapter examines event perception in infancy. To address the question of infants' segmentation and integration of the units of perceptual input, it considers the nature of the auditory and visual environment itself and how it might appear to infants, as well as intermodal events, in particular development of infants' sensitivity to audiovisual information. It also focuses on the broader theme of developmental mechanisms — how it is that emerging sensory skills contribute to developments in cognitive capacities to segment, synthesize, and interpret information to make sense of events. It is shown that despite the dramatic differences between auditory and visual information processing, there are some parallels, such as an analysis of distributional information.

This chapter focuses on the development of internal representations and processes as viewed from the perspective of dual coding theory. Relevant data are interpreted in terms of the assumptions of the theory and, where such data are not available, some testable implications are proposed. The chapter begins with some views concerning developmental mechanisms. It then considers evidence that bears on the verbal-nonverbal representational distinction, functional interconnections between and within the two systems, and the different functional properties associated with them individually and jointly.

This chapter concludes by proposing that the unusual profile of people with WS can best be understood by considering the rich cognitive structures inherent in human spatial representational systems, and their modulation through variation in developmental timing. Contrary to the original description of the cognitive profile of people with WS, the chapter suggests that the profile is remarkably similar to that of much younger normally developing children, both for space and language. This outcome can be understood as the product of highly specialized systems of cognition that emerge along an abnormal developmental timeline. Thus missing genes do not directly cause abnormalities in specific cognitive systems; rather, they target developmental mechanisms that underlie the emergence of all specialized cognitive structures. This hypothesis accounts for a broad range of evidence on the spatial and linguistic profile of people with WS, and sheds new light on how normal development of space and language emerge.

This book examines homology, the correspondence of characters from different species or even within the same organism, from a mechanistic perspective. Homology is explained by derivation from a common ancestor that had the same character or trait. This explanation applies at least to characters from different species. Accordingly, this concept has applications in many fields of biology by referring to morphological characters, behaviors, proteins and genes, gene regulatory networks, and developmental mechanisms and processes. The book considers one class of homology relationships, that between morphological characters, and describes the so-called character identity networks. It argues that the evolutionary origin of characters and body plans is the origin of those gene regulatory networks that underlie character identity.

Due to the finite number of dynamic behaviours that can be implemented by regulatory systems, it should be possible to enumerate and classify different developmental mechanisms that can achieve the same biological function. For example, there are only a small number of ways by which small regulatory networks can create a stripe of gene expression in a static or growing tissue. By comparing these different mechanisms, we can discover the design principles of stripe-producing regulatory networks. Such a rigorous and mechanistic classification scheme would constitute the basis for a theory of development that characterizes and explains the regularities and recurring motifs observed in organismal morphology. This tackles a central question in biology, which has fascinated numerous researchers since the rational taxonomists first raised it in the 19th century. This chapter introduces and defines a concept of developmental mechanism suitable for this endeavour, based on the conceptual framework of dynamical systems theory, which characterizes the dynamical repertoire of regulatory networks. Equivalent mechanisms are defined as sharing the same topology of their phase portraits: they have the same number and geometrical arrangement of attracting states, saddle points, and basins of attraction, and undergo structurally stable bifurcations as systems parameters change over time. These abstract concepts and their application are illustrated using specific examples such as simulated stripe-forming networks, vertebrate limb development, and the segmentation gene network in insects. This constitutes a first, tentative step towards a more general geometrical theory of developmental mechanisms and the complex map from genotype to phenotype.

Where does our understanding of the mind come from? Here we focus on developmental plasticity and argue for a theory-theory account of children’s reasoning about the mind. Two examples are analyzed in depth: infants’ understanding of other people’s visual perspectives and children’s understanding of personality traits. In both we show that providing children particular patterns of evidence—whether about their own experience or about the behavior of others—leads them to create novel and systematic models of the mind. In both cases the idea of a “Bayesian framework principle” is invoked as a formal model of developmental change. It is argued that despite a shared initial state, key aspects of mental life vary in the myriad cultural, physical, and virtual environments human beings create. We show that theory-like inferential abilities, applied to conspecifics’ psychology, is particularly valuable for adapting to, and indeed thriving in that sort of social world.

My goal in writing this book is to change the agenda of the field of cognitive development. In particular, I want to promote greater attention to the question that I believe is inherently at the core of the field: How do changes in children’s thinking occur? Focusing on change may not sound like a radical departure from current practice, but I believe it is. It will require reformulation of our basic assumptions about children’s thinking, the kinds of questions we ask about it, our methods for studying it, the mechanisms we propose to explain it, and the basic metaphors that underlie our thinking about it. That modifications of all of these types are being proposed as a package is no accident. Just as existing approaches have directed our attention away from the change process, so may new ones lead us to focus squarely on it. This concluding chapter summarizes the kinds of changes in assumptions, questions, methods, mechanisms, and metaphors that I think are needed. My initial decision to write this book was motivated by a growing discomfort with the large gap between the inherent mission of the field—to understand changes in children’s thinking—and most of what we actually have been studying. As I thought about the problem, I came to the conclusion that existing assumptions, methods, and theories acted in a mutually supportive way to make what we typically do seem essential, and to make doing otherwise—that is, studying change directly—seem impossible. Even approaches that proclaimed themselves to be radical departures from traditional theories maintained many fundamental assumptions of those theories. An increasing body of empirical evidence, however, indicates that some of the assumptions are wrong and that the way in which they are wrong has led us to ignore fundamental aspects of development. In this section, I describe prevailing assumptions regarding variability, choice, and change, and propose alternatives that seem more consistent with empirical data and more useful for increasing our understanding of how changes occur.

Pittsburgh has many beautiful old houses, most of which have thick plaster walls. The walls are good in the sense that they effectively reduce noise coming from other rooms, but bad in the sense that they sometimes force me to interact with plasterers. My experience with plasterers has not been fun. The ones who have come to do repairs on my house haven’t put drop cloths below where they worked, have resisted or ignored requests not to smoke in the house, and have flicked cigarette ashes wherever they went. Several of them smelled bad and had alcohol on their breath, even at 8:00 A.M. On the other hand, they were really good at plastering. They fixed cracks and holes quickly and without apparent difficulty. The finished product, once painted, matched the surrounding wall or ceiling remarkably well. My own attempts at plastering have been much less successful. These attempts have taught me quite a bit, but unfortunately not how to do the job. I have learned that plastering requires many good strategy choices. Home plastering kits indicate how much plaster powder and water to mix together, and roughly when to apply the mixture, but that is only the beginning of the problem. When exactly has the plaster jelled sufficiently to apply it? If it’s too watery, it will run; if it’s too thick, it will be wavy, and soon will crack. The instructions also do not illustrate the wrist movements for applying the plaster. The package directs the reader to apply the plaster with “flexible,” “supple,” and “smooth” movements, but what does that mean? Despite considerable time spent thinking about how to plaster, and some time spent watching plasterers, my decisions invariably lead to wavy, cracked surfaces resembling those of an artistically challenged kindergaitner. I occasionally have asked the plasterers who came to my house how they know when the plaster is ready and how it should be applied. Their replies: “You just look at it.” “You can see when it’s ready.” “You put it on smoothly.” True enough, I’m sure, but not helpful.