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From Neurons to Neighborhoods: The Science of Early Childhood Development I Setting the Stage
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From Neurons to Neighborhoods: The Science of Early Childhood Development This page in the original is blank.
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From Neurons to Neighborhoods: The Science of Early Childhood Development 1 Introduction Parents have always been captivated by the rapid growth and development that characterize the earliest years of their children's lives. The first responsive smile, the first wobbly step, the first recognizable word—each is a significant personal achievement and an occasion for family celebration. As the months turn to years, unsteady toddling across the living room turns into powerful sprinting across the soccer field, spontaneous smiles evolve into rich friendships, and single words become the building blocks of simple storytelling and, eventually, complex conversations. As the infant becomes a toddler and then a preschooler and finally arrives at his or her first day in kindergarten, parents exclaim, “I can't believe how quickly my baby has grown up!”—and they frequently wonder about whether they have done a good enough job. Scientists also have had a long-standing fascination with the process of early childhood development. The systematic study of infant behavior can be traced back to the early to mid-19th century, when researchers in both embryology and evolution raised fundamental questions about the origins and course of human development across the life span (Cairns, 1998; Kessen, 1965; Maccoby, 1980). By the 1920s, practice-based investigators in the professions of pediatrics, education, and social work were increasing their interaction with psychologists in the world of child study, which led to the establishment of a vibrant, multidisciplinary, scientific discipline that has continued to grow as a blend of theory, empirical investigation, and insights derived from professional experience (Richmond, 1967). One of the most abiding issues explored by developmental scientists,
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From Neurons to Neighborhoods: The Science of Early Childhood Development and the subject of this report, concerns how biological endowment and early experience combine to affect later developmental outcomes. Are the seeds of extraordinary talent present at birth, or are they planted in early childhood? When do early delays in development signal serious problems later in life? Does early intelligence predict lifelong achievement? Do childhood bullies turn into adult criminals? Do early advantages, such as a sunny disposition and skilled parents, inoculate a child from subsequent adversity? Do early harms, such as repeated exposure to family violence, impose irrevocable constraints on subsequent outcomes? Interest in these questions is not new, but there have been significant advances in the understanding of the kinds of changes that occur, and the way those changes are grounded in both “nature” and “nurture.” Over the past three decades, the rate of generation of new knowledge about early childhood development has been staggering. It has led to a number of advances in both concepts and methods—and it promises to increase even further in the near future. This scientific explosion has been fueled by multiple contributions, ranging from theoretical and conceptual advances to dramatic leaps in both the measurement technology and the computer-based analytic capacity available to the behavioral and biological sciences. We are, for example, on the threshold of a revolution in molecular biology grounded in the decoding of the human genome. The prospect of increasing collaboration among neurobiologists, geneticists, and social scientists offers the exciting promise of still greater breakthroughs in understanding the complex interplay between nature and nurture as they jointly influence the process of human development during early childhood. Most recently, increasing interest in the developmental significance of early life experiences has been fueled by extensive media coverage of research on the developing brain. From governors and state legislators to business leaders and entertainers, virtually everyone is talking about the importance of the early childhood period, particularly the first three years of life. This growing excitement has fueled a proliferation of media campaigns and policy activities focused on infants and toddlers, as well as a host of entrepreneurial efforts to capitalize on the demand for materials and experiences to enhance early competence. At the same time, skeptics have stepped forward to question this intense interest in very young children, to point out the limits of contemporary neuroscience, and to underscore the evidence of continuing brain development far beyond the infant-toddler period (Bruer, 1999; Kagan, 1998a). To update what science now tells us about these important issues, the Board on Children, Youth, and Families of the National Research Council and the Institute of Medicine established the Committee on Integrating the Science of Early Childhood Development. The charge to the committee was to review what is now known about the nature of early development and
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From Neurons to Neighborhoods: The Science of Early Childhood Development the role of early experiences, to disentangle established knowledge from erroneous popular beliefs or misunderstandings, and to discuss the implications of this knowledge base for early childhood policy, practice, professional development, and research. The goal, then, is not purely one of summarizing what's new or what's fascinating, but rather one of connecting developmental science to its implications for action and continued inquiry. This is a familiar task for developmental scientists, albeit one that is fraught with difficulties (National Research Council, 1978, 1982; Shonkoff, 2000). Indeed, one of the most distinctive features of the science of early childhood development is the extent to which it evolves under the anxious and eager eyes of millions of parents, policy makers, and professional service providers who seek authoritative guidance as they address the challenges of promoting the health and well-being of young children. Within the framework of its charge, the committee confronted the following kinds of questions. What are the most important developmental achievements that occur from the prenatal period up to school entry? Are there truly “windows of opportunity” in the early years when critical experiences are required for healthy development? When does early adversity seem to have lasting effects? Which aspects of development are relatively robust, and which are more sensitive to differences in the environments in which young children grow up? What aspects of these environments have the most significant influence on early development? What does it take to alter the course of development for the better, and what can we realistically expect from such efforts? How do the answers to these questions vary for children with different strengths and weaknesses, and who are growing up in different circumstances? The answers to these questions define the nature of early development and the responsibilities of adults. Although the committee was most familiar with, and thus most sensitive to, the context in the United States that is now shaping discussion of these issues, it is our firm hope that this review of the scientific evidence will be seen as pertinent to children around the world. The body of research that addresses these questions is extensive, multidisciplinary, and more complex than current discourse would lead one to believe. It covers the period from before birth until the first day of kindergarten. It includes efforts to understand how early experience affects all aspects of development—from the neural circuitry of the maturing brain, to the expanding network of a child's social relationships, and to the cultural values of the society in which parents raise children. It includes efforts to understand the typical trajectories of early childhood, as well as the atypical developmental pathways that characterize the adaptations of children with disabilities. As the knowledge generated by these multiple perspectives has evolved, a number of core concepts have come to frame our understanding
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From Neurons to Neighborhoods: The Science of Early Childhood Development of the nature of early human development. They are summarized here and reemerge repeatedly throughout the report. CORE CONCEPTS Defining the boundaries of science in early childhood development is not an easy task. However, this task can be facilitated for policy makers, practitioners, and parents by differentiating among established knowledge, reasonable hypotheses, and unwarranted assertions (Shonkoff, 2000). Established knowledge is determined by strict rules of evidence and rigorous peer review. It evolves continually over time. Reasonable hypotheses are educated guesses that are derived from, but extend beyond the boundaries of, established knowledge. Although they may be confirmed or disproved by subsequent investigation, they make up a large proportion of the knowledge base that guides responsible policy, service delivery, and parenting practices at any given point in time. Unwarranted assertions distort or misrepresent current knowledge, undermine its credibility, and have the greatest potential to be harmful when they are advanced by those who are viewed as reputable scientists. They are often made to advance commercial goals or an ideological agenda. Ultimately, informed early childhood policy making, effective service delivery, and successful parenting are all dependent on mastery of the existing knowledge base, sound judgment based on reasonable hypotheses, the avoidance of irresponsible practices, and continuous reassessment over time. Understanding of child development is based on multiple sources of knowledge that include theoretical models, empirical research, program evaluation, and professional experience. The role of theory is to provide a framework for organizing what is known and for guiding further investigation. The role of empirical research and program evaluation is to ask important questions (e.g., How do children learn number concepts?) and to test specific hypotheses (e.g., High-quality child care results in language gains for toddlers from high-risk homes), using a variety of quantitative and qualitative methods. The role of professional experience is to tap the wisdom and judgment of people who work with children in a variety of service settings. Taken together, these diverse sources of knowledge advance understanding of the process of child development and enhance the capacity to promote competence, prevent disorders, and correct maladaptive patterns. A set of core concepts frames our understanding of the nature of human development during the earliest years of life and lays a foundation for addressing the following questions: Is early development highly programmed, so that certain events must
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From Neurons to Neighborhoods: The Science of Early Childhood Development happen at predetermined times, or is it more loosely open to environmental influences and primed to seize those that matter most whenever they occur? Do infants follow a smooth and predictable path toward the preschool years (and beyond) or is early growth and development characterized by bumps, detours, and unanticipated turns? Are infants initially incompetent, passive creatures or individuals who are born with an active capability to learn from the surrounding world? Are young children highly vulnerable, highly resilient, or both? The discussion provided in this section reflects the prevailing views of researchers, theorists, and clinicians who study young children. This multidimensional knowledge base has grown exponentially over the past 25 years, fueled by an explosion of scholarly work across a wide variety of disciplines. Its richness lies in the extent to which diverse perspectives have converged on a set of core concepts. Its limitations rest on the extent to which the science is based largely on studies of typical development in white, middle-class samples and developmental vulnerability in samples that do not disentangle race, ethnicity, or socioeconomic status. Focusing on the underlying principles that guide the developmental process, this report highlights ten guiding principles or core concepts. Human development is shaped by a dynamic and continuous interaction between biology and experience. Early pioneers in the field of child study approached the complexity of human development by devising simple models and testing them. Some, such as Arnold Gesell (1925, 1929), believed that the emergence of skills is driven primarily by genes. Others, such as John B. Watson (1928), believed that all behaviors are determined by the environment. These early models reflected a mechanistic conceptualization of development that was derived from the physical sciences. Over time, it became increasingly clear that humans do not behave like machines (neither the prewired nor the programmable type), and children began to be viewed through the lens of modern biology, rather than that of classical physics or chemistry. Consequently, human development is now described in interactive terms (i.e., “dynamic”), reflecting the essential characteristic of a living organism. Virtually all contemporary researchers agree that the development of children is a highly complex process that is influenced by the interplay of nature and nurture. The influence of nurture consists of the multiple nested contexts in which children are reared, which include their home, extended family, child care settings, community, and society, each of which is embedded in the values, beliefs, and practices of a given culture. The influence of
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From Neurons to Neighborhoods: The Science of Early Childhood Development nature is deeply affected by these environments and, in turn, shapes how children respond to their experiences. In simple terms, children affect their environments at the same time that their environments are affecting them. Moreover, no two children share the same environment, and no environment is experienced in exactly the same way by two different children. Two youngsters living in the same home influence each other and are affected by the other members of the family in unique ways. If one child is active and aggressive and the other is passive and subdued, each will elicit different responses from the parents—and each will be influenced differently by the behavior of the other. These concepts reflect what Sameroff and Chandler (1975) characterized as the transactional nature of the developmental process and what Bronfenbrenner (1979) described as the ecology of human development (also see Horowitz, 1999). This transactional-ecological model of development provides a useful framework that moves far beyond the misleading and tired old nature-nurture debate. It helps people think in more sophisticated ways about the complex determinants of successful adaptation and health as well as those of maladaptation and disorder. It offers insights into how the same behavioral disposition may be adaptive in one context and not in another. It also fits well with what scientists are learning about the dynamic nature of the development of the brain. Children vary in their behavioral style. Some are high-strung and some are laid-back; some are agile and some are clumsy. Children are raised in a wide variety of social circumstances and cultural contexts. Some conditions are secure and others are unstable; some encourage competition and others promote cooperation. Behaviors that are highly adaptive in one society (e.g., competitiveness among preschoolers in the United States) may not be so in another (e.g., individual assertiveness among preschoolers in Japan). Different childrearing environments promote distinctive patterns of skill development in some children and not in others (e.g., some may reinforce active, physical performance while others encourage quiet, artistic expression). At every level of analysis, from neurons to neighborhoods, genetic and environmental effects operate in both directions (Gottlieb, 1992). On one hand, the gene-environment interactions of the earliest years set an important initial course for all of the adaptive variations that follow. On the other hand, this early trajectory is by no means chiseled in stone. The considerable degree of developmental plasticity that characterizes an immature organism is embodied in the capacity of its cells to adapt in very specific ways, in both the short and the long run, to changing demands. Neurons grow new axons, sprout new dendrites, form new synapses, and modify the strength of some established connections while eliminating others selectively over time. The impacts of varied experiences are also reflected in
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From Neurons to Neighborhoods: The Science of Early Childhood Development observed differences in the brain's blood supply, its cellular (glial) support systems, its intercellular insulation (myelin), the neurochemicals that it produces, and the specific receptors that recognize each individual substance. These concepts are taken up in more detail in Chapter 2 and Chapter 8. Culture influences every aspect of human development and is reflected in childrearing beliefs and practices designed to promote healthy adaptation. The influence of culture on the rearing of children is fundamental and encompasses values, aspirations, expectations, and practices. Understanding this realm of influence is central to efforts to understand the nature of early experience, what shapes it, and how young children and the culture they share jointly influence each other over the course of development. The effects of culture on child development are pervasive. It prescribes how and when babies are fed, as well as where and with whom they sleep. It affects the customary response to an infant's crying and a toddler's temper tantrums. It sets the rules for discipline and expectations for developmental attainments. It affects what parents worry about and when they begin to become concerned. It influences how illness is treated and disability is perceived. It approves certain arrangements for child care and disapproves others. In short, culture provides a virtual how-to manual for rearing children and establishes role expectations for mothers, fathers, grandparents, older siblings, extended family members, and friends. Given the magnitude of its influence on the daily experiences of children, the relative disregard for cultural influences in traditional child development research is striking. The literature on typical development is based overwhelmingly on studies of middle-class children of European-American ancestry, often involving samples drawn from university communities. In contrast, much of the research on children of color has focused on the impacts of poverty, drawing its samples from homogeneous communities in high-risk urban environments. Moreover, relatively little is known about the impacts of racism and other forms of systematic discrimination on early childhood development, independent of the adverse effects of low maternal education and socioeconomic status. Consequently, knowledge of the full range of environmental influences on young children and their relation to typical variations during early childhood is highly skewed and incomplete. hardship and minority group status is severely compromised (Garc ía Coll and Magnuson, 2000). The influence of cultural context on early childhood development is widely acknowledged. The empirical literature in this area, however, is underdeveloped. This weakness in the knowledge base is particularly problematic in view of the increasing racial and ethnic diversity of the population of the United States. In short, the basic concept is compelling, the
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From Neurons to Neighborhoods: The Science of Early Childhood Development database is thin, and the imperative for extensive research is clear. These issues are taken up in more detail in Chapter 3. The growth of self-regulation is a cornerstone of early childhood development that cuts across all domains of behavior. Regulation is a fundamental property of all living organisms. It includes physiological and behavioral regulations that sustain life (e.g., maintenance of body temperature and conversion of food into energy), as well as those that influence complex behaviors (e.g., the capacity to pay attention, express feelings, and control impulses). Regulatory processes modulate a wide variety of functions to keep them within adaptive ranges. The simultaneous operation of these multiple systems at different levels of organization is an essential feature of human development, as we discuss at length in Chapter 5. A broad range of everyday experiences in early childhood are subject to regulation. In addition, for some children, atypical stresses can overwhelm their baseline regulatory capacities. Experience with manageable challenges (e.g., briefly having to wait to be fed or soothed) promotes healthy regulatory abilities. Repeated exposure to stresses that are overwhelming (e.g., severe malnutrition, chronic abuse) may result in significant maladaptation or disorder. Individual differences in regulatory capacities are rooted in both biological endowment and life experience. For example, the underlying neurobiology of irritability and poor attention may be affected by neurotransmitters in the central nervous system that are determined by either genetics or a chaotic environment. More commonly, regulatory dispositions involve the interplay between both endowment and experience. As children mature, their capacity to exert their own autonomous control over key regulatory functions is essential. Advances in motor skills make it possible for preschoolers to feed themselves when they are hungry and put on a sweater when they are cold. Cognitive and emotional maturation signals a greater ability to delay gratification, to sit still to read a book, and to cope with the stresses of separation or loss. Thus, development may be viewed as an increasing capacity for self-regulation, not so much in the specifics of individual behaviors but in the child's ability to function more independently in personal and social contexts (Bronson, 2000; Kopp, 2000; Sameroff, 1989; Sroufe and Waters, 1977). The behaviors children use to regulate themselves and their environments change in meaning as they get older. What is considered typical and adaptive at one age may not necessarily be viewed in a comparable fashion at another age. Crying, for example, is an early regulatory behavior that in infancy sends important signals to caregivers, yet it may become a sign of social immaturity if it is used repeatedly to express frustration in middle childhood. Adaptive behaviors also can have costs, such as the hypervigilance needed to survive in a physically dangerous environment. Finally,
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From Neurons to Neighborhoods: The Science of Early Childhood Development the socialization process and meaning of some regulatory behaviors, such as physical aggression and delayed gratification, differ across cultures. Consequently, adaptations essential to survival in one context may be maladaptive in another. Children are active participants in their own development, reflecting the intrinsic human drive to explore and master one's environment. The inborn drive to master the environment is a basic feature of human development throughout the life cycle (White, 1959), as we illustrate throughout Part II of this volume. Shortly after birth, children begin to learn about the world through their remarkable capacities to create their own knowledge from early experience. This inborn thrust is facilitated by the extent to which their environments provide opportunities and supports for growth. Parents and the general public wonder about which experiences are necessary for healthy development to unfold. Must these experiences be costly? Do they require expensive educational toys and early access to computers? The simple answer to such questions is generally “no.” Given the drive of young children to master their world, most developmentalists agree that the full range of early childhood competencies can be achieved in typical, everyday environments. A cabinet with pots and pans, for example, seems to serve the same purpose as a fancy, “made for baby” musical instrument. An extensive body of multidisciplinary research supports the notion of powerful inborn tendencies toward mastery that are apparent in earliest infancy. Piaget (1952) labeled this characteristic cognitive assimilation and considered it to be a basic fact of life. Others have called it mastery motivation (e.g., MacTurk and Morgan, 1995), emphasizing the experience of pleasure in performing newly acquired behaviors and skills. Fraiberg pointed out that this developmental thrust enhances efforts to direct development along positive pathways, commenting, “it's a little bit like having God on your side” (Fraiberg et al., 1980, p. 53). Reviewing previous research on early development, Emde (1990) specified aspects of this developmental thrust and proposed that they act as key ingredients for behavioral interventions throughout the life span. In this regard, all forms of early childhood intervention are most effective when they counteract obstacles to growth and promote the expression of a child's natural drive toward mastery. Human relationships, and the effects of relationships on relationships, are the building blocks of healthy development. From the moment of conception to the finality of death, intimate and caring relationships are the fundamental mediators of successful human adaptation. Those that are created in the earliest years are believed to differ from later relationships in that they are formative and constitute a basic structure within which all
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From Neurons to Neighborhoods: The Science of Early Childhood Development meaningful development unfolds. Because many of the regulatory systems that are essential for infant survival and emotional organization require consistent caregiving attention, it has been said (perhaps too dramatically) that without the caregiver-infant relationship, there would be no infant (Winnicott, 1965). The essential features of healthy, growth-promoting relationships in early childhood are best embodied in the concepts of contingency and reciprocity. That is to say, when young children and their caregivers are tuned in to each other, and when caregivers can read the child 's emotional cues and respond appropriately to his or her needs in a timely fashion, their interactions tend to be successful and the relationship is likely to support healthy development in multiple domains, including communication, cognition, social-emotional competence, and moral understanding (Brazelton et al., 1974; Emde, 1980; Stern, 1977). Developmental or behavioral disturbances in infants and toddlers are embedded in disturbances of the caregiver-infant relationship (Ainsworth, 1973; Bowlby, 1973; Sameroff and Emde, 1989). Because babies depend for their survival on the care of adults, it is difficult, if not impossible, to consider their problems independent from their relationships with their primary caregivers. For example, a young child may be difficult to soothe, but whether this characteristic expresses itself as a disorder that requires therapeutic attention will depend on the way it affects and is handled by the child's primary caregivers. Some adults may view such behavior as overwhelmingly negative (“he is spoiled, selfish, and unreasonable”), whereas others may see it as a positive trait (“she knows her own mind and won't settle for less than what she wants”). Most successful interventions, whether they are primarily preventive or therapeutic, are based on facilitating that relationship and helping both the child and the caregiver learn to adapt successfully to each other's individuality. These issues are taken up in more detail in Chapter 9, Chapter 11, and Chapter 13. The broad range of individual differences among young children often makes it difficult to distinguish normal variations and maturational delays from transient disorders and persistent impairments. Developmental competencies vary significantly across a wide range of individual differences, and the rank ordering of children according to their abilities changes over time. Within this broad continuum, it often can be difficult to make clear distinctions among individual differences within a normative or typical range (e.g., variations in communication skills), transient delays related to maturational lags (e.g., speech articulation errors), and diagnosed developmental disabilities (e.g., true disorders of language or cognition), especially in the early childhood years. A related issue is the fact that so many defining symptoms for disorders are also nonspecific indications that some-
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From Neurons to Neighborhoods: The Science of Early Childhood Development thing is not quite right. This applies to depression, inattention, overactivity, and anxiety—all of which can be displayed by a child who has a fever or is overly tired, as well as by a child with a specific disorder. In part, these difficulties are related to the limitations of existing developmental measures. To a large extent, however, diagnostic dilemmas are inherent in the complex and unpredictable nature of early childhood development (Boyce, 1996). All children have built-in capacities to attain developmental goals in multiple ways and under varying conditions. This is illustrated in the phenomenon of alternative developmental pathways, which provides a useful model for understanding the distinctive competencies that children develop in diverse cultural contexts, as well as the different family patterns of interaction that promote their unfolding (Erikson, 1950; Pumariega and Cross, 1997). The concept of alternative developmental pathways offers a framework for viewing individual differences, maturational delays, and actual disabilities as part of a unified continuum that applies to the development of all children. The early child-caregiver relationship, for example, can be stressed by either biological or environmental threats, yet the processes governing the relationship are organized in a comparable manner, even for children with significant impairments or for those whose development is at very high risk (Cicchetti and Beeghly, 1990; Sameroff and Emde, 1989). Similarly, all developmental transitions are susceptible to the adverse impacts of a wide range of risk factors that can produce a sense of elevated uncertainty, regardless of the nature of the child or the caregiving context (Wishart, 1993). Ultimately, such patterns are understood best when they are viewed as variations within a common developmental framework. Children born with significant biological impairments (e.g., blindness, deafness, severe motor deficits) also attain a range of basic abilities, such as representational thinking and language competence, in ways different from those experienced by children without such limitations. Greater understanding of these alternative pathways can provide guidance for interventionists in their attempts to facilitate the adaptive development of young children with a wide variety of special needs, as well as in their efforts to extend constructive support to their parents (Decarie, 1969; Fraiberg, 1977; Gleitman, 1986). These issues are further discussed in the context of the specific developmental tasks described in Part II. The development of children unfolds along individual pathways whose trajectories are characterized by continuities and discontinuities, as well as by a series of significant transitions. The process of development is essentially a process of change. In some cases (e.g., increasing memory functions), that change appears to be gradual, cumulative, and continuous.
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From Neurons to Neighborhoods: The Science of Early Childhood Development In other cases (e.g., the beginning of expressive language and self-awareness in the second year), the gains are so far-reaching that they represent a qualitative discontinuity from what has come before (Brim and Kagan, 1980; Rutter and Rutter, 1993). Such transformations are often referred to as developmental transitions. These transitional phases, which may be either smooth or characterized by stress and turmoil, have been viewed as important periods of psychological reorganization that provide useful opportunities for intervention (Brazelton, 1992). Developmental transitions occur throughout the life span, but in the early childhood years they are more frequent and involve profound psychobiological changes. A developmental transition can be thought of as a time when change is pervasive and enduring, and when it involves a major reorientation in how a child relates to the environment. It is a time when the emotional communication between children and caregivers is particularly significant (Emde, 1998). Developmental transitions are periods of psychological disequilibrium that reflect elements of both the stage that is being completed and the stage that is about to begin. The intense negativism of toddlers, who are attempting to reconcile strong feelings of attachment to their parents and a powerful drive for personal autonomy, is a familiar example of this complex phenomenon. These issues are taken up in more detail in Part II. Human development is shaped by the ongoing interplay among sources of vulnerability and sources of resilience. Individual developmental pathways throughout the life cycle are influenced by interactions among risk factors that increase the probability of a poor outcome and protective factors that increase the probability of a positive outcome (Garmezy et al., 1984; Rutter, 2000; Werner, 2000). Risk factors may be found within the individual (e.g., a temperamental difficulty, a chromosomal abnormality) or the environment (e.g., poverty, family violence). Protective factors also may be constitutional (e.g., good health, physical attractiveness) or environmental (e.g., loving parents, a strong social network). The cumulative burden of multiple risk factors is associated with greater developmental vulnerability; the cumulative buffer of multiple protective factors is associated with greater developmental resilience. Sameroff, Seifer, Barocas, Zax, and Greenspan (1987) have demonstrated that the total number of risk factors in a child's life is a better predictor of IQ scores than the specific nature of those factors. The double burden of both biological and environmental risk produces an unusually high level of vulnerability (Escalona, 1982; Parker et al., 1988; Shonkoff, 1982). Some developmental pathways follow trajectories or patterns that are deeply ingrained and thus less amenable to influences that may deflect them in a positive or negative direction. Others are highly susceptible to such risks and protective influences. Waddington (1966) compared these path-
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From Neurons to Neighborhoods: The Science of Early Childhood Development ways to the valleys and ridges that are formed by a ball rolling downhill. The further the ball rolls along a given path, the deeper are the valleys and the steeper are the ridges. Developmental characteristics that are embedded in deeply chiseled trajectories (e.g., basic motor capacities, such as crawling and walking) are less amenable to environmental modification and are described as canalized. Other trajectories have valleys that are more shallow or ridges that are less steep, which leave them more susceptible to change (e.g., basic self-care skills, early literacy). Ultimately, the extent to which any existing pathway can be modified or redirected is determined by both biological and environmental influences. The child's own expectations, and those of the significant people in his or her life, often play an important role in maintaining or changing direction. These concepts are especially pertinent to the literature reviewed in Part III regarding the contexts for early development. The timing of early experiences can matter, but, more often than not, the developing child remains vulnerable to risks and open to protective influences throughout the early years of life and into adulthood. Human adaptation derives from both the rapid consolidation of essential capacities and lifelong flexibility to adjust to changing circumstances (see Chapter 8). Efforts to understand which aspects of development become set early on and which remain open to change have been shaped by notions of critical and sensitive periods, as well as by a growing research literature on the malleability or plasticity of the human organism. The concepts of both critical and sensitive periods refer to unique episodes in development when specific structures or functions become especially susceptible to the influence of particular experiences (Bornstein, 1989; Thompson, in press(a)). Although critical periods have been well described for several behaviors in a variety of animal species (e.g., imprinting in newborn geese), the term “sensitive period” is preferred when studying humans because it implies less rigidity in the nature and timing of the required experiences, as well as less inevitability in its developmental outcome (Immelmann and Suomi, 1982). Current knowledge suggests that, although developmental progress in some domains may be relatively more amenable to facilitation or vulnerable to harm during certain periods in comparison to others (see, for example, the discussion of institutionalization in Chapter 9 and of family income in Chapter 10), advances can occur at virtually any age. The concept of developmental plasticity refers to the capacity of the brain to reorganize its structure or function, generally in response to a specific event or perturbation. Although it is determined fundamentally by genetic modification, plasticity often comes about as a result of a change in the environment (see Chapter 2 and Chapter 8). Times of developmental transition,
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From Neurons to Neighborhoods: The Science of Early Childhood Development which are often characterized by major alterations in person-environment relationships, provide important opportunities for understanding this critical adaptive phenomenon. Neurodevelopmental plasticity varies inversely with maturation. That is to say, there is more multipotentiality (i.e., greater capacity for alternative developmental adaptations) in the early childhood period than in the later years. The course of development can be altered in early childhood by effective interventions that change the balance between risk and protection, thereby shifting the odds in favor of more adaptive outcomes. Although the desire to learn, grow, and “become” is inherent in the biology of early childhood, it is also a characteristic that is open to modification based on individual experience. When the environment supports a child 's emerging sense of agency (i.e., the feeling of being able to influence events and thus having an impact on one's own life), his or her motivation to act on the world flourishes. When experience fails to support (or punishes) such action, a child's motivation diminishes, shifts, or finds problematic outlets. Early environments that facilitate competence and a sense of personal efficacy are more likely to foster children who do well. When opportunities for agency are limited, psychological growth is more likely to be compromised. A wide variety of early intervention policies and programs have been designed to create growth-promoting environments for young children whose development is threatened by biological vulnerability or adverse life circumstances (see Chapter 13). Different models employ varying combinations of strategies focused on providing direct experiences for the child, influencing the behaviors of the child's primary caregivers and/or working directly on the child-caregiver relationship. The basic objective underlying all interventions in the early childhood years is to increase the probability of a more favorable developmental trajectory for each child. This is accomplished by attempting to identify and mitigate the influence of existing risk factors, as well as to identify and enhance the buffering capacity of available protective factors. This often occurs in the context of specific therapeutic or educational services. Individual goals are determined in terms of each child's and family's baseline status in conjunction with an assessment of the extent to which relevant risk and protective factors are susceptible to change. In the final analysis, early childhood intervention is viewed most appropriately as an individualized strategy designed to increase the probability of a desired outcome, and not as a developmental panacea for all children under all circumstances. It is the art of the possible, based on the science of early childhood development.
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From Neurons to Neighborhoods: The Science of Early Childhood Development SCOPE OF THE STUDY The committee's charge to identify the implications of its scientific review was directed at three interrelated goals: (1) to inform the design and implementation of policies, services, and professional training to support the health and development of young children and their families; (2) to stimulate the formulation of an integrated research agenda to advance both the basic science of early childhood development and the applied science of early childhood intervention, extending from the prenatal period through the preschool years; and (3) to educate the public about state-of-the-art knowledge regarding human development during early childhood. The committee did not set out to produce a comprehensive handbook on early childhood development, nor did we seek to provide explicit parenting advice. We selected topics that are especially pertinent to current debates about the early childhood years and sought to help readers understand young children rather than to offer directive statements about how to raise them. Indeed, with such understanding comes humility about the complexity of the task undertaken by anyone who brings up a child, and an appreciation for the value of a firm grounding in “what develops?” and “how?” as a departure point for highly personal decisions involved in day-to-day childrearing. To select the issues on which it would focus, the committee conducted a series of interviews with practitioners and policy makers to assess their views of the most pressing issues facing contemporary early childhood practice and policy, as well as with scientific colleagues in fields ranging from basic neuroscience to anthropology and sociology. The committee also reviewed a broad range of previous reports produced by the National Research Council and the Institute of Medicine and, with few exceptions (e.g., child care, prenatal alcohol exposure), did not conduct new reviews of areas addressed previously (see Appendix A for a listing of pertinent reports). Appendix A includes a number of reports that address issues of physical health and nutrition that, while not explicitly addressed in this report, are a vitally important foundation for every aspect of development we discuss. The science summarized in this report reflects the expertise and judgment of the members of the committee, who were themselves selected for their breadth of knowledge and interdisciplinary scope. The analyses that contributed to this report draw on a variety of sources. The committee reviewed a wide body of research through targeted literature searches and direct correspondence with investigators known for their work on specific topics. Between October 1998 and February 2000, the committee met six times to identify critical issues, analyze available data, discuss research findings, seek additional information on specific ar-
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From Neurons to Neighborhoods: The Science of Early Childhood Development eas of concern, formulate conclusions and recommendations, and prepare this report. Three additional subcommittee meetings were convened to discuss pertinent literatures on neuroscience, culture and early human development, and methodological issues. Three workshops—on home visiting interventions, precursors of antisocial behavior, and the science of early childhood intervention (National Research Council and Institute of Medicine, 2000)—and five commissioned papers1 also contributed valuable scientific input to the committee's work. PLACING THE STUDY IN CONTEXT One hundred years ago, the transition from the 19th to the 20th century marked a time of significant energy, creativity, and attention to the health and well-being of the nation's children. The overlapping emergence of child development as a focus within the field of psychology, pediatrics as a specialization within the practice of medicine, and child welfare as a defined domain within the purview of both the judicial system and the world of social work provides just a few examples of the extent to which the distinctive needs of children began to appear more clearly on the social and political agenda (National Research Council, 1981, 1982). In 1912, Congress established the Children's Bureau in the Department of Labor, which proceeded to conduct studies in such diverse areas as infant mortality, day care, institutional care, and mental retardation (Lesser, 1985). Ten years later, as a growing database documented the strong association between socioeconomic factors and infant and maternal deaths, public health nursing services and state child hygiene divisions were expanded under the provisions of the Sheppard-Towner Act of 1921 (Steiner, 1976). As the crown jewel of the New Deal, the passage of the Social Security Act of 1935 formalized an expanded federal responsibility for the health and well-being of children and their mothers. Title V of the act authorized financial assistance to the states to support: (1) a broad array of maternal and child health services, including prenatal care, well-baby clinics, immunization programs, and nutrition services, with a special emphasis on underserved rural and low-income populations; (2) comprehensive services for “crippled children”; and (3) a range of child welfare services for the care and protection of homeless, dependent, and neglected youngsters (Magee 1 Topics were: the demographics of the birth to five age group, atypical language development, the developmental consequences of community violence, regulation of attention and executive function in young children, and the effects of prematurity on early brain development. In addition, over two dozen experts in the area of culture and early development were invited to respond to a brief questionnaire about key topics developed by the committee.
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From Neurons to Neighborhoods: The Science of Early Childhood Development and Pratt, 1985). Another provision of the act, Aid to Dependent Children (later renamed Aid to Families with Dependent Children) ensured a federal entitlement to a guaranteed baseline of economic security for vulnerable children and their mothers. Three decades after the onset of the New Deal, under the broad umbrella of the Great Society and the War on Poverty, the modern era of early childhood intervention was launched with the creation of Head Start and the initiation of the Handicapped Children's Early Education Program (Smith and McKenna, 1994; Zigler and Valentine, 1979). Whereas Title V of the Social Security Act had strengthened the nation's medical focus on the consequences of low income and childhood disability, the policies of the 1960s spearheaded an education strategy. Fifteen years later, during a period of significant reduction in federal social programs and devolution of authority to the states, Head Start continued to be funded as a part of the government's “safety net,” and a new federal entitlement to early intervention services for infants and toddlers with disabilities was enacted under Part H of the Education for All Handicapped Children Act Amendments of 1986 (Public Law 99-457), and reauthorized in 1997 as Part C of the Individuals with Disabilities Education Act (Public Law 105-107) (Meisels and Shonkoff, 2000). The current social, economic, and political contexts within the United States in which this report will be read and interpreted have once again changed. In recent years, federal legislation has been enacted to expand the financing of child health care through the State Children 's Health Insurance Program under Title XXI of the Social Security Act (Public Law 105-33), yet the 60-year entitlement to welfare support for families with young children has been terminated by the Personal Responsibility and Work Opportunity Reconciliation Act of 1996. Greater investment in education reform garners strong public support, universal school readiness is ranked first among the nation's education goals, and the demand for higher standards and stricter accountability in the public schools is widely endorsed. And yet, despite two high-profile White House conferences on child care and early childhood development and significant increases in public funding for early child care and education at both the federal and state levels, there is still widespread and well-entrenched resistance to the formulation and enforcement of more rigorous standards for child care providers and the settings in which they work. And despite the creation and expansion of Early Head Start for infants and toddlers, services for 3- and 4-year-olds are still available to less than half of the eligible children in the United States, more than 30 years after the opening of the first Head Start center in 1965 (Meisels and Shonkoff, 2000). Beyond specific government policies and programs, the context of this report is reflected in a set of highly interrelated social, economic, and
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From Neurons to Neighborhoods: The Science of Early Childhood Development political challenges presently facing children, their parents and other caregivers, and U.S. society in general. These include: (1) dramatic changes in the nature of work, an increasingly strong link between education and employability, and greater difficulty for families at all income levels in balancing workplace and family responsibilities; (2) ongoing increases in the racial and ethnic diversity of the U.S. population and the persistence of significant racial and ethnic disparities in health and developmental outcomes; (3) the persistent poverty of young children and a growing gap between the wealthy and the poor; (4) continued high rates of community and family violence, as well as serious mental health problems that impose significant burdens on family functioning; (5) an increased reliance on market solutions to address complex social problems; (6) the devolution of some important responsibilities for the implementation of child and family policy to the state and local levels; and (7) conflicting views about the role of government and the balance between public and personal responsibility for the health and well-being of children. The release of this report also comes at a somewhat sensitive time in the politics of early childhood intervention in the United States. Evaluations of a wide range of model programs and community-based replications have produced results both encouraging and disappointing, posing a critical challenge to those who are seeking to understand the conditions under which success is more likely than failure. This is also a time of significant expansion in state and local initiatives designed to improve the life chances of very young children. Fueled by headlines about the importance of the early years, as well as by increased national interest in school readiness, education reform, and the early roots of antisocial behavior and violent crime, this heightened public concern raises critical questions about which investments are most likely to make a significant difference for the most vulnerable young children. In this context, the most important task facing the committee is not to differentiate specific intervention programs that “work” from those that do not. Rather, it is to provide a scientifically grounded portrait of the most important achievements of early childhood and the environmental conditions that either promote or impede their accomplishment, and to point to directions for both action and further research toward those ends. This report addresses two complementary agendas. The first is focused on the future and asks: How can society use knowledge about early childhood development to maximize the development of the nation' s human capital and ensure the ongoing vitality of its democratic institutions? The second is focused on the present and asks: How can the nation use knowledge to nurture, protect, and ensure the health and well-being of all young children as an important objective in its own right, regardless of whether measurable returns can be documented in the future? The first agenda
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From Neurons to Neighborhoods: The Science of Early Childhood Development speaks to society's economic, political, and social interests. The second speaks to its ethical and moral values. The committee is clear in our responsibility to speak to both. ORGANIZATION OF THE REPORT The organization of this report reflects its charge. Part I sets the stage for understanding the material that follows. This introduction has presented an overview of the core concepts that guided the committee's inquiry. Chapter 2 takes up a reconceptualization of the long-standing debate about the interaction between nature and nurture. Chapter 3 summarizes current thinking about the multifaceted concept of culture and its role in early human development, and Chapter 4 raises important methodological issues regarding efforts to explore questions about causality in early development and early intervention. Part II addresses the central question of the nature of early development. What develops during the earliest months and years of life? What are the major behavioral and developmental tasks of the early childhood period? When should we worry? This part of the report starts with the child's emerging capacity for self-regulation, reflecting a shift in what developmentalists now believe to be a hallmark of early development (Chapter 5). Next, we turn to the remarkable accomplishments in language and learning that characterize this age period (Chapter 6) and the critical challenges associated with getting along with other children (Chapter 7), both of which represent areas of heightened interest on the part of parents, practitioners, and policy makers alike. Chapter 8 provides an updated review of research on early brain development. It comes last, reflecting the fact that developmental neuroscience is a recent addition to the study of the child. Furthermore, processes of brain development are better understood when considered in relation to the significant and concurrent emotional, mental, and social advances of early childhood. Part III turns to the role of early environments as they shape early development. The chapters review research on the multiple, overlapping contexts in which development unfolds, beginning with the most active ingredient of early environmental influences, namely the parent-child relationship (Chapter 9). We then discuss the contribution of the economic niche occupied by the family (Chapter 10), the influence of child care (Chapter 11), and the role of the community in which the child lives (Chapter 12). Together, these chapters paint a vivid picture of the environments and experiences that foster or impede adaptation and well-being. Chapter 13 is a critical overview of the scientific foundations of early childhood intervention, thereby complementing what is known about early develop-
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From Neurons to Neighborhoods: The Science of Early Childhood Development ment as it unfolds naturally over time with a view based on efforts to alter its course. The committee's charge to draw out the implications of its research review is addressed in the final chapter (Chapter 14), which provides conclusions and makes recommendations for policy, practice, and professional development, as well as for research.
Representative terms from entire chapter: