When we began our longitudinal studies in the 1970s there was great skepticism regarding the lasting role for early experience in human development (e.g., Clarke & Clarke, 1976
). Early longitudinal work, such as the Fels study, had indeed shown only modest continuity and virtually none from the first 3 years of life to later periods (Kagan & Moss, 1962
). This and other findings led Kagan (1984)
to argue that life was like a tape recorder with the record button always on, such that new experiences would write over and replace earlier experiences. However, early studies were based on linear, homotypic models of continuity and/or focused on rather robust aspects of cognitive development. The question remained whether more developmentally appropriate assessments, more complex models, and assessments that included social and emotional aspects of development would be more successful.
Recently, of course, due to advances in neuroscience, there has been an upsurge of interest in early experience and persuasive demonstrations of its power to impact development, primarily based on animal studies. Studies have now shown that normal brain development requires relevant experience (“experience expectant” brain development; Greenough, Black & Wallace, 1987
) and that variations in experience can produce notable differences in brain structure and even the expressions of genes (e.g., Black, Jones, Nelson, & Greenough, 1998
; Kaffman & Meaney, 2007
; Nelson & Bosquet, 2000
; Marshall & Kenney, 2009
; Stiles, 2008
). The human data currently available are limited, speculative regarding specific brain systems, and based almost solely on quite extreme variations in experience, such as institutionalization (e.g., Gunnar, 2001
; Rutter, Kreppner, & Sonuga-Barke, 2009
). Still, at this point no one doubts that human brain development depends upon the experience of the individual (e.g., Schore, 2002
Despite the outpouring of work in neuroscience, there remains considerable skepticism in developmental psychology that more typical variations in early human experience significantly influence the course of development, with arguments often centering on the transformative effects of subsequent experience (e.g., Harris, 1998
; Lewis, 1998
). In addition, little has been heretofore known about specific kinds of linkages that might be more pronounced, about the mechanisms of change, about the fate of early experience following developmental change, or about developmental processes that promote continuity when it is found. These were all issues we were able to address to some extent in our longitudinal study.
The Minnesota longitudinal study of parents and children has followed 180 individuals from 3 months before birth to now age 34 years (e.g., Erickson, Sroufe, & Egeland, 1985
; Sroufe, Egeland, & Kreutzer, 1990
; Sroufe, Egeland, Carlson, & Collins, 2005b
; Vaughn, Waters, & Egeland, 1979
). The children were born into poverty, leading to a substantial range in quality of care and developmental outcome. The study was well cast to assess the impact of early experience, as well as a host of other features of development, because measures were detailed, comprehensive, and densely gathered in all age periods. Direct observation, as well as formal assessments and parent interviews, were utilized age by age, including 8 assessments in the first 18 months. The study tapped all domains of development (cognition, language, socio-emotional) and multiple arenas (home, school, laboratory, and peer group). Beginning early, we were able to assess temperament in infancy, as well as quality of care over time. Many aspects of parenting were examined, including provision of a secure base for attachment, structure and limit setting, and cognitive stimulation. Finally, the broader developmental context was assessed (e.g., parent characteristics, family life stress, and social support), for purposes of statistical control and to provide factors that might influence continuity and change in child development.
Evaluating the role of variations in early human experience turns out to be more complicated than first meets the eye. There are a number of complexities. First, it is clearly not always the case that early experience is most critical. Prenatal development provides excellent examples of both early and later events being important (DeHart, Sroufe, & Cooper, 2004
). Numerous teratogens, including many drugs and viruses, have dramatically more profound affects in the first trimester of pregnancy when basic organ systems are first forming. Often the timing is exquisite, wherein a teratogen with devastating effects in the early weeks has no effect whatsoever a week or two later. The presumption is that this is due to the disruption of normal differentiation. For example, brain neurons can migrate, interconnect, and organize into systems only if the neurons are formed in the first place. This is compelling. However, maternal nutrition during pregnancy is a dramatic contrary example. While certain nutrients like folic acid are critically important in the early embryonic period, poor general
maternal nutrition has almost no demonstrable effects in the first trimester, because the tiny developing organism can simply take many of the nutrients it needs from maternal stores. However, in the third trimester, when rapid fetal size and weight gain is occurring, adequate maternal nutrition is crucial to prevent babies born too small for gestational age, a serious risk for compromised development.
A classic study by Schaffer and Callender (1959)
provides an interesting example from postnatal life. Infants hospitalized in the first few months of life showed few negative reactions or readjustment problems. In contrast, babies older than 7 months protested mightily, were negative toward the hospital staff, and needed a period of readjustment upon returning home. Likewise, a group of infants who experienced early caregiving instability, but were adopted by age 4 months, showed no decrease in security of attachment (Singer, Brodzinsky, Ramsay, Steir, & Waters, 1985
). These examples call attention to the more general issue of timing. Systems appear to be most vulnerable when they are emerging. Thus, “early” is a relative concept, being anchored by developmental considerations. We will provide other such examples later in the paper.
Second, it is often the case that the consequences of earlier and later experience are cumulative or are seen primarily in the context of other risk factors. For example, experimental deprivation studies with rhesus monkeys showed that those deprived in the first 6 months of life (equivalent to more than a year in human terms) later were more socially handicapped than those isolated for the second 6 months (Sackett, 1968
; Suomi, 1977
). However, those monkeys that were deprived for the entire
first year were clearly more handicapped than those monkeys deprived for just the first 6 months, important as that was. A classic study by Cadoret and colleagues (Cadoret, Troughton, Merchant, & Whitters, 1990
) found that an early experiential risk factor (number of placements prior to adoption or age of permanent placement) by itself had rather little power in predicting later depression; however, in concert with a genetic risk factor (biological mother diagnosed with depression) there was notable predictive power. The genetic risk factor also had little impact by itself. In our own research we found that disorganized attachment in infancy predicted later dissociative symptoms, but it did so much more strongly if there was subsequent abuse (Ogawa, Sroufe, Weinfield, Carlson, & Egeland, 1997
). These are just a few of many possible examples. It should be noted, however, that such considerations do not negate the role of early experience; to the contrary, they suggest that its role might be best appreciated when considered within a broader view of development.
Third, and related to the above, the potential impact of early experience may at times be transformed by subsequent experience; that is, there may be change away from an early trajectory. As one example, the observation that premature birth did not have negative consequences in the context of middle class environments spurred development of the widely influential “transactional model” of Sameroff and Chandler (1975)
. Research documented that premature infants tend to catch up over the first year or two of life in a supportive, middle class context (Crockenberg, 1981
; Sigman, Cohen, Beckwith, & Parmelee, 1981
), apparently because parents in supportive contexts are prompted to increase their responsiveness to such needy infants (Cohen & Beckwith, 1979
). This is a case where a negative early event leads to subsequent corrective experience. In our work we find that changes in parental life stress, social support, or depression are frequently associated with changes in early developmental trajectories (Sroufe, Egeland, Carlson, & Collins, 2005b
). Other, more complex examples will be presented below.
Many specific outcomes of interest are likely sensitive to particular experiences at varying points in time. Sometimes what is happening during or just before a period of development may be as much or more important than what happened years earlier. At the least, the particular outcome, the particular kind of experience under study, and age will all be relevant.
Beyond all of these issues, there are important process questions surrounding the role of early experience; that is, how does early experience have its impact? And how does it interact with later experience to produce developmental outcomes? A related question concerns why what appear to be similar early experiences have apparent consequences for only some individuals. These issues currently are often discussed in terms of moderation and mediation. Thus, the primary question is not whether early experience is more important than later experience, but, rather, what is the (and when is there a) particular role for early experience in development? In general, early experience can be conceptualized in terms of creating vulnerabilities or strengths with regard to later experience, including what experiences are sought and how they are interpreted, rather than as directly producing particular outcomes.
Thus, certain patterns of adaptation may be established early in development and then have their power because of their impact on the subsequent environment. That is, at times early experience sets in motion a chain of experiences each impacting the next, such that if at any time forestalled, the impact of early experience would no longer be seen. In this way, for example, a child who has adopted an understandable strategy of withholding emotional expression due to rejection in the face of expressed need may later isolate himself from others and thereby preclude the corrective experiences that could alter the early pattern (Sroufe, 1983
). From a non-linear process view, early experience often would have its affect indirectly through an on-going transaction between child and environment.
Our prospective longitudinal study from prenatal life to adulthood provided an opportunity to wrestle with these complexities, as well as to examine the power of early experience for predicting an array of outcomes. In conducting this research we were guided by a transactional, hierarchical, and “cumulative pathways” model of development (e.g., Bowlby, 1973
; Sameroff & Chandler, 1975
; Werner, 1948
). Bowlby (1973
, p.412) summarized a core feature of this viewpoint in the following way: “Development turns at each and every stage of the journey on an interaction between the organism as it has developed up to that moment and the environment in which it then finds itself.” In this perspective, development is not determined by early experience, but by the cumulative history of the child interacting with the environment. The early years merit special attention because the initial adaptations they promote become the starting place for subsequent transactions, framing how new experiences are engaged. Thus, again, the primary question concerns not the relative importance of early experience but the particular nature of its role in development. Moreover, in this view early experience may be transformed but is not erased by subsequent experience, as is argued by some theorists (e.g., Kagan, 1984
; Lewis, 1998
). It remains in force. Thus, the position is unique in simultaneously postulating that early experience is not deterministic yet always remains a part of the developmental landscape.
On subsequent pages we will provide empirical examples to illustrate each of the issues outlined above. At the same time, our detailed, comprehensive study allowed us to resolve a number of methodological problems that plague efforts to demonstrate any role for typical variations in early experience. Even with prospective, longitudinal data, numerous controls are needed to infer any kind of causal connection between an early obtained measure and a later outcome. For example, correlations between early rejecting care and later school problems or conduct problems could be due to a variety of factors. The question of common genetic factors could be raised. Perhaps, for example, parent low IQ accounts for both rejecting parenting and child problems. Alternatively, perhaps irritable child temperament leads to the rejecting care in the first place and indirectly (or directly) to later child problems. Finally, rejecting care may be a pattern that is continued from the early years to the later years, and it may be care at the later time is actually responsible for the child behavior problems, not the early care at all. Comprehensive, age by age assessments of parenting, child factors, IQ of parent and child, life stress, and social support, among other things, are required to begin addressing these potential confounds. Our array of empirical examples will illustrate how we coped with these methodological problems.