Developmental Systems Theory Accounting for Stability and Variability

Developmental Systems Theory: Accounting for Stability and Variability at Different Time Scales Robert Lickliter Florida International University Miami, FL

The 19 th century novelist, satirist, and amateur biologist Samuel Butler once said: “Life is like giving a concert on the violin while learning to play the instrument”

Butler’s insight that development occurs “in the middle of things” was a brilliant observation and highlights one of the key insights common to both dynamic systems and connectionist approaches to development: development is activity and experience based (and as I hope to show, activity and experience can have very long-term effects)

Dynamic Systems and Connectionist approaches to development both agree that: developmental outcomes are realized in large part by the real-time events that organisms encounter and take part in as they live their lives thus, nothing in biology or psychology makes sense except in the light of its own history

Developmental Explanation This is so because we know that development is a multilevel affair involving the physical and social environments, anatomy, physiology, hormones, and genes of the developing organism. Any outcome (genetic activity, neural activity, behavior) is necessarily the result of a large set of prior internal and external developmental resources and processes. In other words, all phenotypic outcomes have a specific developmental history that helps to explain their emergence.

Requirements of Developmental Explanation Given that developmental processes occurring at various time scales both generate the reliable reproduction of form and function (stability) and introduce variation in form and function (variability) observed within and across individuals, a complete theory of development must account for both stability and variability over time

Development results from changing relationships over various time scales between a structured organism and a structured environment developing organism developmental milieu (genes, hormones, neural systems, etc. ) (physical, biological, and social environments)

Dynamic and Connectionist approaches to development certainly appreciate these themes and a significant dividend of both approaches has been to emphasize • the historical and contingent nature of the developmental process (time and timing matter) • the need for a theory that accounts for both the stability and variability of form and function seen within and across individuals

What is Different About A Developmental Systems Approach? Building on its conceptual and empirical roots in developmental psychobiology, a developmental systems view holds that phenotypes are generated from constructive interactions among multiple recurrent resources (e. g. , “the developmental system” including genes, cellular machinery, the reliable presence of physical and biological features of the habitat, social resources, and the results of previous development) (not that different from connectionist and dynamic systems assumptions)

What is Different? • However, a central concern of a developmental systems approach is the identification of the developmental processes that allow for the repeated assembly of these constructive interactions within and across generations (recurrences of the developmental system) • Advances in our understanding in this area can allow us to finally lay to rest the worn dichotomies of nature vs. nurture, genes vs. environment, etc. which continue to plague content areas within both the biological and psychological sciences

A Developmental Systems Approach Environment Behavior Neural Activity Genetic Activity Individual Development an emphasis on the bi-directional traffic between levels, see Gottlieb, 1991

Common Themes Across Dynamic and Developmental Systems Approach • Nonpreformationism: developmental information is not preformed and is not limited to genes; it appears in a wide range of developmental resources, including genes, cells, and hormones, as well as physical, biological, and social environments • Context Sensitivity and Contingency: whether resources for development come together as required (the right place at the right time) is a contingent affair involving networks of interactions • Distributed Causality: causal power or control for phenotypic outcomes resides in the contingent relations between these distributed developmental resources and interactants

In addition, a developmental systems approach emphasizes • Extended Inheritance: genes are but one of many inherited developmental resources; heredity transmission involves the reliable reconstruction of resources-in-interactive networks across generations This emphasis additional complexity to our notions of time scales

there are nested levels of time • real time – the immediate experiences and encounters of the organism with its physical, biological, and social environment • developmental time - the continuing influence of past experiences on the organism’s ongoing interaction with its environment • evolutionary time – the transgenerational effects of the organism’s experiences during its individual ontogeny

The role of transgenerational effects • a focus on the transgenerational effects of the organism’s activity and experiences during individual ontogeny has a long history in developmental psychobiology (e. g. , Denenberg, Levine) and represents an important contribution to current concerns with the sources of stability and variability in development • this body of work has shown that activity and experience may not only affect the development of the parental phenotype, but also can guide and constrain offsprings’ reaction to available developmental resources and environmental influences

Intergenerational Transfer of Experience these parental effects can impact offspring development at a number of points in time: • while the (maternal) gametes are developing prior to fertilization • in the post-fertilization phase of offspring development (fetal effects) • postnatally (for example, in the case of the well documented neural and physiological effects of maternal grooming on young rodents)

For example, early handling and enriched environment studies have provided a range of dramatic findings, including that modified early experience in one generation can influence physiological and behavioral developmental outcomes in subsequent generations even in the absence of the experiential modification early handling increased exploration, problem solving, and novelty seeking in offspring and grandoffspring

Transgenerational Influences That is, developmental modifications can be transmitted across generations in the absence of the original, precipitating conditions (such parental effects on offspring have been demonstrated in a wide array of organisms, affecting traits ranging from egg size, growth rate, resistance to pathogens, reaction to stress, etc. ) How this transgenerational inheritance of experience works and the underlying biology involved remains poorly understood, as does its developmental and evolutionary implications (significant advances are, however, being made at the genetic, cellular, hormonal and behavioral levels of analysis)

The Value of a Developmental Systems Approach Developmental Systems Theory has a unique role to play in defining and describing the links between development and evolution, in large part because its aims, purposes, and time-scales are not the well represented in other complementary approaches to development (e. g. Dynamic and Connectionist approaches)

The Value of a Developmental Systems Approach These include: • a concern with the developmental dynamics contributing to both the stability and variability of form and function observed across generations • a concern with the role of behavioral development in the evolutionary process - particularly in generating novel phenotypes, which can then be subjected to the filter of natural selection, providing an engine for evolutionary change

possible evolutionary consequences For example, animals that have had considerable variation in social and physical experiences early in life appear more likely to seek out variation later in life, showing greater levels of exploratory behavior, problem solving, and novelty seeking than animals having more limited early experience

possible evolutionary consequences This sort of behavioral plasticity increases the likelihood of particular individuals utilizing or migrating to new environments, where they might encounter different types of functional demands from their surround Although many changes in functional demands would be transient, others could be long lasting and persist across generations, resulting in morphological, physiological, or behavioral variability not typically expressed in original environments

making sense of evolution requires making sense of development Given that all phenotypic characters arise during ontogeny as products of individual development, the only way for evolutionary change to occur is by variation in the patterns of development that give rise to individual phenotypes Contrary to the dogma of the last century, development is thus a key ingredient in understanding evolution – and developmental systems theory is positioned to continue to provide empirical and conceptual advances in the integration of developmental theory with evolutionary theory

thanks to: • John Spencer and Jay Mc. Clelland for organizing this conference forum • National Institute of Mental Health, National Institute of Child Health and Human Development, and the National Science Foundation for support of my research and scholarship • Collaborators: Gilbert Gottlieb, Lorraine Bahrick, Hunter Honeycutt • Graduate students and post-docs: Rebecca Markham, Mark Jaime, Chris Harshaw, and Susan Schneider