A Unified Theory of Development: A Dialectic Integration of Nature
and Nurture
Arnold Sameroff
University of Michigan
The understanding of nature and nurture within developmental science has evolved with alternating ascen-
dance of one or the other as primary explanations for individual differences in life course trajectories of suc-
cess or failure. A dialectical perspective emphasizing the interconnectedness of individual and context is
suggested to interpret the evolution of developmental science in similar terms to those necessary to explain
the development of individual children. A unified theory of development is proposed to integrate personal
change, context, regulation, and representational models of development.
The attention of philosophers and then scientists to
human development has always begun with a con-
cern that children should grow up to be good citi-
zens who would contribute to society through
diligent labor, moral family life, civil obedience,
and, more recently, to be happy while making these
contributions. The mo tivation for these concerns
was that there were many adults who were not.
Although attention was paid to the socialization
and education of children, it was ultimately in the
service of improving adult performance. The socie-
tal concern has always had a life-span perspective.
Without healthy, productive adults no culture
could continue to be successful. This concern
continues to be a major motivator for society to
support child development research. Although the
intellectual interests of contemporary develop-
mental researchers range widely in cognitive and
social–emotional domains, the political justification
for supporting such studies is that they will lead to
the understandi ng and ultimate prevention of
behavioral problems that are costly to society.
With these motivations and supports there have
been major advances in our understanding of the
intellectual, emotional, a nd social behavior of
children, adolescents, and adults. Moreover these
understandings have increasingly involved multi-
level processes cutting across disciplinary bound-
aries in the social and natural sciences. This
progress has forced conceptual reorientations as
earlier unidirectional views that biological or social
circumstance controlled individual behavior are
becoming multidirectional perspectives where indi-
vidual behavior reciprocally changes both biologi-
cal and social circumstance.
The models we use to understand how individ-
uals change over time have increased in complex-
ity from linear to interactive to transactive to
multilevel dynamic systems. Was this progression
in complexity an expression of empirical advances
in our developmental research or is it relate d to
more general progressions in the history of science
as a whole? Several years ago during a discussion
of a need for a critical social history of develop-
mental psychology by a number of distinguished
scientists (Bronfenbrenner, Kessel, Kessen, &
White, 1986), Sheldon White argued that it is nec-
essary to engage and deconstruct the history of the
field in parallel with efforts to understand the
child. He contin ued by pointing out that the study
of development needs a self-concept, just as each
child requires ‘‘the building of some kind of self-
referential, self-regulating, self-knowing set of
structures.’’
If there is a more soph isticated understanding of
the development of humans, is there a more sophis-
ticated understanding of the development of our
science? The models we use to understand the his-
tory of our field from child psychology to develop-
mental science should increase in complexity.
Understanding developmental science requires
developmental science. And as in the study of any
Correspondence concerning this article should be addressed to
Arnold Sameroff, Center for Human Growth and Development,
University of Michigan, 300 N. Ingalls Building, Ann Arbor, MI
48109-0406. Electronic mail may be sent to sameroff@umich.edu.
Child Development, January/February 2010, Volume 81, Number 1, Pages 6–22
2010, Copyright the Author(s)
Journal Compilation 2010, Society for Research in Child Development, Inc.
All rights reserved. 0009-3920/2010/8101-0002
historical process there should be hope that under-
standing the past will help us predict the future.
The premise of the general systems theories that
arose in the 1930s was that there were gene ral prin-
ciples of organization in every scientific domain
that were at a level of abstraction somewhere
between mathematical formulations and the spe-
cific processes being studied (Boulding, 1956). Thi s
has become apparent in every discipline from phys-
ics to political science, as each has moved to models
of dynamic regulation, where parts cannot be sepa-
rated from wholes and useful predictions can only
be made based on local interactions of multiple sys-
tems. The hope of the founders of general systems
theory (cf. von Bertalanffy, 1968) was that scientists
would use a top-down strat egy to interpret empiri-
cal data from a complexity perspective (Sameroff,
1983). This aspiration was not realized because each
science has tried to be as theoretically simplistic as
possible, resisting the demise of deterministic mod-
els until overwhelmed by the complexity of empiri-
cal data. The science of psychology has been no
exception.
Developmental research aspired to the dicta of
Ockham’s razor in the hope of finding simple basic
elements and processes that would explain the
emergence of life’s comp lexity. Up through the
1960s and into the 1970s statistically significant
t tests and analyses of variance gave an illusion that
science was advancing, but when regression mod-
els became dominant and the metric changed to
size of effects (Cohen, 1988), it became clear that
the field was not doing well at explaining how chil-
dren were growing up. Contemporary developmen-
talists are quite competent at short-term predictions
of similar cognitive or emotional constructs but
much worse at the prediction of long-term success-
ful life adaptations starting from initial conditi ons.
Increasingly, sophisticated statistical models have
been sought to separate the behavioral signal of
interest from the noise of real life. This effort has
led to some frustration in the decreasing amounts
of variance that can be attributed to any single fac-
tor when every thing imaginable is controlled and
obscured the possibility that the unexplained vari-
ance, the noise, might contain the signals of many
other dimensions of the individual or context that
are necessary for meaningful long-term predictive
models.
Applicability may not be the most salient criteria
for getting research accepted for publication, but it
is highly salient for suggesting ways to change
developmental outcomes. The science paid for by
the public is increasingly being asked to meet a
translational rather than a statistical crite rion with
the application of research to policy an important
consideration (Huston, 2008). The primary question
remains as to how we can improve the fate of indi-
viduals growing up in our society. To answer that
question requires a continuing examination of the
models we need both to study and to understand
development. In what follows I will present a con-
temporary summary of what such mode ls should
contain and offer a suggestion for an integrated
view of development that captures much of the var-
iance that needs explaining. No part of what I pro-
pose has not been previously suggested by creative
others. Combining these elements into a unified
developmental theory acknowledges the contempo-
rary zeitgeist moving toward more dynamic con-
ceptualizations at every level of analysis that is
taking place in every other scientific discipline.
A Rough History of the Nature Versus Nurture
Question
Before comp lexity was simplicity. For developmen-
tal explanations, simplicity was expressed in
appeals to aspects of an individual’s nature or nur-
ture. The history of developmental psychology has
been characterized by swings between opinions
that determinants of an individual’s behavior could
be found either in their irreducible fundamental
units or in their irreducible fundamental experi-
ences. The growth process between babyhood and
adulthood could be explained either by appeals to
intrinsic properties of the child or to extrinsic prop-
erties of experience. The nature–nurture question
has been a central content of developmental
research, but it can also be considered to be a major
context for developmental research in its appeal to
deterministic thinking. As a consequence the his-
tory of the nature–nurture question can be used as
an organizing construct to understand the history
of our field.
Practically, the nature–nurture question comes
into play when a child has a problem and the ques-
tion arises, ‘‘Who is responsible?’’ Most parents’
first response is to blame the child and most profes-
sionals’ first response is to blame the parents. How-
ever, most scientists know that it is both. It is both
child and parent, but it is also neurons and neigh-
borhoods, synapses and schools, proteins and
peers, and genes and governments. But that conclu-
sion does not explain how it is both. Do natur e and
nurture interact deterministically so that the pro-
portions attributable to each can be decomposed or
Unified Theory of Development 7
do they transact probabilistically so that the contri-
bution of each can only be an abstraction from the
activity of dynamic systems? How this question has
been answered in the course of recent history offers
a window into how developmental science has
evolved and a perspective on how the question will
be answered in the future.
Since ancient times philosophers have weighed
in with their perspectives on the relative influences
of constitution and experience in determining the
life course, but it is in the last few hundred years
that these positions have been well articulated,
most notably John Locke in the 17th century and
Rousseau in the 18th. I will begin my rough histori-
cal account in the late 19th century with the begin-
nings of empirical psychological research in the
work of Francis Galton (see Table 1). Francis Galton
coined the ‘‘nature versus nurture’’ phrase and in
his view inherited characteristics were the origins
of human nature. The nurture counterpoint was
most strongly stated in the work of John Watson in
the 1920s who propounded a new approach he
labeled behaviorism, extending Pavlov’s condition-
ing processes to explain human individual differ-
ences. Learning theory came to dominate human
developmental research for almost 50 years
strengthened by the operant paradigms promoted
in the work of the Skinnerians.
This tilt toward nurture began to shift in the
1960s under assault from three directions—ethol-
ogy, behavioral genetics, and the cognitive revolu-
tion. Where S-R theorists had argued that the laws
of learning were primary in explaining develop-
mental change, ethologists were demonstrating that
many complex behaviors did not seem to need any
reinforcement (Lorenz, 1950) and that S-R contin-
gencies that worked in one species did not work in
another (Breland & Breland, 1961). For example,
rats could learn to push a lever to avoid a
shock but pigeons could not. Ethologists argued
that the nature of the species put large restrictions
on the effects of nurture such that certain
prepared responses were impervious to experience
(Seligman, 1970). Statist ical advances and data from
large samples of twins permitted behavioral gene-
ticists to argue that the effects of genes and envi-
ronments could be separate d, a nd that very large
proportions of behavioral differences could be
explained by genetic differences (Defries &
McLearn, 1973). The cognitive revolution character-
ized in the work of Jean Piaget placed the source of
development in the mind of the child. Experience
was necessary for the child to construct the world
but it did not play a role in individual differences.
Where the nativist shift in the 1960s was driven
by advances in biological science, the nurturist shift
in the 1980s was driven by three advances in the
social science—the war on poverty, the concept of a
social ecology, and cultural dec onstruction. Where
behaviorist research focused on proximal connec-
tions between reinforcements and performance, sci-
entists in other social disciplines were arguing that
economic circumstance was a major constraint on
the availability of reinforcements, such that the
developmental environments of the poor were
deprived in contrast with those of the affluent. Sim-
ilar individuals in different social classes would
have quite different developmental outcomes.
Bronfenbrenner (1977) in his vision of the social
ecology offered a more differentiated model than
provided by economics alone. He identified the
distal influences of family, school, work, and
culture on the availability of reinforcements to the
child, providing a more comprehensive empirical
model for predicting individual differences in
development. The influence of postmodernist
deconstruction was manifest in the emergence of a
cultural psychology that went beyond cross-
cultural descriptive studies. Meaning rather than
behavior became dominant through demonstrations
that the same child behaviors could be given
different meanings in different societies leading
to different developmental consequences, and
conversely, different behaviors could be given the
same mea ning leading to the same consequences.
The new millennium coincided with another
swing of the pendulum in the nativist direction,
again tied to major advances in biological science.
Neuroscience and molecular biology have been
making major contributions to our understanding
Table 1
Rough History of Nature–Nurture
Historical era Empirical advance
1880–1940s—Nature Inherited differences
Instincts
1920–1950s—Nurture Reinforcement theory
Psychoanalytic theory
1960–1970s—Nature Ethology—species differences
Behavioral genetics
Cognitive revolution
1980–1990s—Nurture Poverty
Social ecology
Cultural deconstruction
2000–2010s—Nature Molecular biology
Neuroscience
8 Sameroff
of development with new technologies for imaging
the brain and manipulati ng the genome. But, as
will be discussed below, the more recent swings
between nature and nurture have been getting
shorter and their intermingling has been increasing.
An examination of Table 1 emphasizes the
swings between the popularity of nature and nur-
ture as developmental explanations. At each point
in time there are strong adherents of both positions
waiting for some new technological advance to
reinforce their point of view. Although this polarity
provides motivation for empirical innovation, it has
the unfortunate side effect of inhibiting theoretical
innovation. Despite the alternating claims that the
argument is now closed by those on the frontier of
new explorations of nature or nurture, the fact
remains that after each advance most of the vari-
ance in long-term developmental outcomes is still
unexplained. It is the pressure of unexplained vari-
ance that continually negates claims of ascendancy
and dialectically motivates continuing exploration.
I have presented a descriptive case for the
cycling of exp lanations between nature and nurture
to raise the question if there is an explanation of
the repetitive pattern. It could be interpreted as
simply the result of technological or theoretical
advances, but it also could be a phenomenon in
itself. The development of the nature–nurture
debate might follow developmental principles simi-
lar to those that regulate human development and
the examination of the two in parallel might illumi-
nate both.
Nonlinear Models of Development
An appreciation of cycling requires an appreciation
of a number of nonlinear processes that I will dis-
cuss under the general rubric of dialectical theory
with specific attention to a developmental helix and
processes of differentiation and integration. Dialec-
tics have been directly or indirectly emphasized for
studying develop ment and especially relationships
(Hinde, 1997; Riegel, 1976). An initial appro ach to
dialectics is best captured by consideration of the
Taoist diagram of the dark yin and the light yang
(see Figure 1) that emphasizes that opposites are in
a mutu ally constituting relationship. They were cre-
ated together and remain bound to each othe r. This
philosophical statement is empirically validated at
the most fundamental level of physics where
quarks, the cu rrent basic entities, are always in a
relationship with each other. At the most funda-
mental level of the universe there are no ultimate
units, only ultimate relationships. In the dialectical
yin–yang there is a unity of opposites and an inter-
penetration of opposites. The unity is indicated by the
mutual embrace of the yin and the yang, as seen in
the figure, but yin and yang also interpenetrate
each other as depicted by the small black spot of
yin within the yang and small white spot of yang
within the yin.
In the psychological realm these ideas have been
applied frequently, beginning with the philosophi-
cal writings of Hegel and most manifest in Piaget’s
theory of cognitive development. There is a unity
of opposites between one’s cognitions and the
world that is being cognize d. Without the world
there would be nothing to cognize, and without the
cognizer there would be no cognitions. But there is
also an interpenetration of opposites. One’s cogni-
tion leads to one’s action which becomes part of the
world (the small black dot in the white area), and
then the changed world becomes a part of one’s
cognition (the small white dot in the black area) in
a continuing dialectica l progression.
The dialectical perspective on nature and nurture
is that they mutually constitute each other. There is
a unity of opposites in that development will not
occur without both, and there is an interpenetration
of opposites in that one’s nature changes one’s nur-
ture and conversely one’s nurture changes one’s
nature, as captured in current transactional models.
Moreover, and most salient, without the one, the
other would not exist. Species and their enviro n-
ments evolved together in a coactive and transac-
tional relationship. Gottlieb’s (1992) construct of
probablistic epigenesis centered on the joint regula-
tion by organismic and experiential factors that
produced development with neither having priority
over the other. The reciprocal bootstrapping
between cultural change in groups and cognitive
Figure 1. Unity of opposites and interpenetration of opposites in
yin and yang diagram. Nu = nurture; Na = nature.
Unified Theory of Development 9
change in individuals is well articulated by Cole
(2006) in his description of human phylogeny.
Although Galton and Watson are the straw men
that nurturists and nativists, resp ectively, rail
against, both appreciated the unity of constitutions
and environments. Galton (1876) recognized the
influence of social class and wrote, ‘‘Nature pre-
vails enormously over nurture when the differences
of nurture do not exceed what is commonly to be
found among persons of the same rank in society
and in the same country.’’ Watson (1914), in turn,
recognized that individual and species differences
were important, ‘‘effectiveness of habit training
would be facilitated by knowledge of an animal’s
individual instinctive responses.’’ The unity and
interpenetration of nature and nurture will be more
fully explored in the unified model of development
to follow.
The Developmental Double Helix
The dynamic dialectical interplay betwee n oppo-
sites can best be captured as an image of a helix
that depicts the developmental aspects of changes
over time as can be seen in Figu re 2a. A simple
example of a developmental progression is the
daily cycle where spiraling to the right would be
the movement toward day and spiraling left would
be the movement toward night. Although this is a
repetitive cycle, it becomes helical in that each day
is different because of the experience of the previ-
ous night and each night is different because of the
experience of the preceding day. A more complex
example would be the development of representa-
tion in children (Werner, 1948). Initially, infants
represent the world as images of here and now
experiences. Preschoolers cycle over the same mate-
rial but now have the capacity to depict images in
drawings that may have a one-to-one correspon-
dence to the images but are not the same as the
images. In a few years they will recycle over the
same contents but now with the ability to do
abstract representations such as maps where the
pictorial aspects may be completely eliminated in
favor of words and symbols. Such developmental
recycling also occurs in the social-emotional
domain where relationship experiences and repre-
sentations derived from early parent–child relation-
ships are reworked as children enter into peer
relationships and reworked again in the romantic
relationships beginning in adoles cence. Erikson
(1959), although not known for his empiricism, was
very articulate in describing the recycling of iden-
tity issues that are never resolved but through a
balancing of opposites provide the impetus for each
succeeding stage. The figure of the helix empha-
sizes that the same issues in a variety of domains
are revisited again and again during development.
The ubiquity of this helical concept is even found
in Graduate Record Examination practice questions
Figure 2. (a) Developmental helix. (b) Differentiation and integration of helix. (c) Developmental double helix of nature and nurture.
10 Sameroff
