300 word essay comparing and contrasting Erickson's and Piaget's Child Development Theories and an "A Conception of Adult Development" article

A Conception of Adult Development Daniel J. Levinson Yale University

ABSTRACT: Adult development is becoming an important field o f study for psychology and other disciplines. Little has been done, however, to conceptualize the nature o f adult development and to define the major issues in this field. The author summarizes his own formulations o f life course, life cycle, life structure, and the adult development o f the life structure in early and middle adulthood. He then discusses six major issues that must be dealt with by every structural approach to adult development: What are the alternative ways o f defining a structural stage or period? What relative emphasis is given to the structures as compared to the transitional periods? How can we make best use o f the distinction between hierarchical levels and seasons o f development? Are there age-linked develop- mental periods in adulthood? What are the relative merits and limitations o f various research methods? How can we bring together the developmental perspective and the so- cialization perspective?

The study of adult development is, one might say, in its infancy. It has been taken seriously in the human sciences for only the past 30 years or so, largely under the impact of Erikson's (1950, 1958, 1969) germinal writings. Er- ikson's most obvious contribution was his theory of stages in ego development. What is less obvious is that his view of development is deeply grounded in his conceptions of the life cycle and the life course. Each ego stage has its primacy at a particular age level or segment of the life cycle, from infancy to old age. The sequence of age seg- ments and ego stages thus provides a representation of the life cycle as a whole; the meaning of a stage is defined in part by its place in the total sequence. In addition, his developmental concepts arose out of his primary concern with the individual life course: the process of living, the idea of life history rather than case history, the use of biography rather than therapy or testing as his chief re- search method. Without abandoning the distinction be- tween self (psyche, personality, inner world) and external world (society, culture, institutions, history), he gave first consideration to the life course--the engagement of self with world.

Although a good deal has been learned since the 1950s about specific features of adult life, very little has been done to advance the general theory of adult devel- opment. At the same time, various fields of psychology (such as child development, gerontology, personality, so- cial, clinical, and counseling psychology), as well as the social sciences and humanities, are becoming more aware that they n e e d - - a n d lack--an adult development per- spective. Adult development is, in short, a significant

problem for psychology as a discipline and an important link between psychology and other disciplines, including sociology, biology, and history.

I have two primary aims here. First, I will present my conception of adulthood and of a developmental pro- cess within it. My intention is to explicate a theoretical position, not to prove it nor to argue for its superiority over others. The theory originated in my initial study of men's lives (Levinson, 1977, 1978). It has evolved over the last few years, particularly through my current re- search on women's lives (Levinson, in press). It is sup- ported by a number of other studies (e.g., Gooden, 1980; Holt, 1980; Kellerman, 1975; Levinson, 1984; Stewart, 1976), but a great deal must yet be done to test and modify it. The theory includes the following elements: (a) The concepts of life course and life cycle, which provide an essential framework for the field of adult development; within this framework, studies of one process or age level can be connected to others, but without it, we have a miscellany of findings and no integrated domain of in- quiry; (b) the concept of the individual life structure, which includes many aspects of personality and of the external world but is not identical with any of these and evolves in its own distinctive way; and (c) a conception o f adult development--the evolution of the life structure in early and middle adulthood. Life structure development is different from, and should not be confused with, the development of personality, social roles, or other com- monly studied processes.

Second, I will discuss adult development as a field of study. I will consider six major issues that help to define what the field is about and what work must be done to establish it more securely. The list is not complete, but it provides a useful starting point. Reference will be made to the work of others, but the main goal is to clarify my own position. Let it be clear that my aim is not to give a comprehensive review of the work in this field nor to seek consensus among the disparate approaches. I hope that others will be stimulated to present contrasting views.

T h e L i f e C o u r s e

Life course is one of the most important yet least ex- amined terms in the human sciences. It is a descriptive term, not a high-level abstraction, and it refers to the concrete character of a life in its evolution from beginning to end. Both words in this term require careful attention.

The word course indicates sequence, temporal flow, the need to study a life as it unfolds over the years. To study the course of a life, one must take account of sta- bility and change, continuity and discontinuity, orderly progression as well as stasis and chaotic fluctuation. It is

January 1986 �9 American Psychologist Copyright 1986 by the American Psychological Association, Inc. 0003-066X/86/$00.75 Vol. 41, No. 1, 3-13

n o t enough to focus solely on a single m o m e n t ; nor is it enough to study a series o f three or four m o m e n t s widely separated in time, as is ordinarily done in longitudinal research. It is necessary, in Robert White's (1952) felic- itous phrase, to examine "lives in progress" and to follow the temporal sequence in detail over a span o f years.

The word life is also o f crucial importance. Research on the life course must include all aspects o f living: inner wishes and fantasies; love relationships; participation in family, work, a n d other social systems; bodily changes; good t i m e s and b a d - - e v e r y t h i n g that has significance in a life. To study the life course, it is necessary first to look at a life in all its complexity at a given time, to include all its components a n d their interweaving into a partially integrated pattern. Second, one must delineate the evo- lution o f this pattern over time.

The study o f the life course has presented almost insuperable problems to the h u m a n sciences as they are now constituted. Each discipline has claimed as its special d o m a i n one aspect o f life, such as personality, social role, or biological functioning, a n d has neglected the others. Every discipline has split the life course i n t o disparate segments, such as childhood or old age. Research has been done from such diverse theoretical perspectives as biological aging, moral development, career development, adult socialization, enculturation, and adaptation to loss or stress, with m i n i m a l recognition o f their interconnec- tions. The resulting fragmentation is so great that n o dis- cipline or viewpoint conveys the sense o f an individual life and its temporal course.

The recognition is slowly dawning that the m a n y specialties and theoretical approaches are not isolated entities but aspects o f a single field: the study o f the in- dividual life course. During the next decade, this study will emerge as a new multidisciplinary field in the h u m a n sciences, linking the various disciplines. With the for- mation o f a more comprehensive, systematic conception o f the life course, the parts will become less isolated and each part will enrich the others.

T h e L i f e C y c l e

The idea o f the life cycle goes beyond that o f the life course. In its origin this idea is metaphorical, n o t de- scriptive or conceptual. It is useful to keep the p r i m a r y imagery while moving toward more precise conceptual- ization a n d study. The imagery o f "cycle" suggests that there is an underlying order in the h u m a n life course; although each individual life is unique, everyone goes through the same basic sequence. The course o f a life is n o t a simple, continuous process. There are qualitatively different phases or seasons. The metaphor o f seasons ap- pears in m a n y contexts. There are seasons in the year. Spring is a t i m e o f blossoming, and poets allude to y o u t h

I would like to thank my wife, Judy D. Levinson, for her contributions to the substance and spirit of this article and my colleague, Boris M. Astrachan, for his intellectual, moral, and administrative support.

Correspondence concerning this article should be addressed to Daniel J. Levinson, Department of Psychiatry, Yale University School of Medicine, 34 Park St., New Haven, CT 06519.

as the springtime o f the life cycle. S u m m e r is the season o f greatest passion a n d ripeness. An elderly ruler is "'the lion in winter.'" There are seasons within a single d a y - - dawn, noon, twilight, the full dark o f n i g h t m e a c h having its counterpart in the life cycle. There are seasons in love, war, politics, artistic creation, and illness.

The imagery o f the life cycle thus suggests that the life course evolves through a sequence o f definable forms. A season is a major segment o f the total cycle. Change goes on within each season, and a transition is required for the shift from one to the next. Every season has its own time, although it is part o f and colored by the whole. No season is better or more i m p o r t a n t t h a n a n y other. Each has its necessary place a n d contributes its special character to the whole.

W h a t are the major seasons in the life cycle? Neither popular culture nor the h u m a n sciences provide a clear answer to this question. The m o d e r n world has no estab- lished conceptionmscientific, philosophical, religious, or l i t e r a r y ~ o f t h e life cycle as a whole a n d o f its c o m p o n e n t phases. There is no standard language t h a t demarcates and identifies several gross segments o f the life cycle. The p r e d o m i n a n t view, rarely stated explicitly, divides it into three parts: (a) an initial segment o f about 20 years, in- cluding childhood and adolescence (preadulthood); (b) a final segment starting at a r o u n d 65 (old age); a n d (c) be- tween these segments, an amorphous time vaguely known as adulthood.

A good deal is known about the preadult years, which for a century have been the m a i n province o f the field o f h u m a n development. The developmental per- spective has been o f crucial importance here. The idea is now accepted that in the first 20 years or so all h u m a n beings go through an underlying sequence o f p e r i o d s ~ prenatal, infancy, early childhood, middle childhood, pubescence, and adolescence. Although all children go through c o m m o n developmental periods, they grow in infinitely varied ways as a result o f differences in biolog- ical, psychological, and social conditions. In its concrete form, each individual life course is unique. The study o f preadult development seeks to determine the universal order and the general developmental principles t h a t gov- ern the process by which h u m a n lives become increasingly individualized.

Historically, the great figures in the study o f child development, such as Freud and Piaget, have assumed that development is largely completed at the end o f ad- olescence. Given these assumptions, they had no basis for concerning themselves with the possibilities o f adult development or with the nature o f the life cycle as a whole. An impetus to change came in the 1950s when geriatrics and gerontology were established as fields o f h u m a n ser- vice and research. Unfortunately, gerontology has n o t gone far in developing a conception o f the life cycle. One reason, perhaps, is that it skipped from childhood to old age without examining the intervening adult years. Pres- ent understanding o f old age will be enhanced when more is known about adulthood; thus, old age can be connected more organically to the earlier seasons.

4 J a n u a r y 1986 �9 American Psychologist

There is now very little theory, research, or cultural wisdom about adulthood as a season (or seasons) o f the life cycle. We have no popular language to describe a series of age levels after adolescence. Words such as youth, maturity, and middle age are ambiguous in their age link- ages and meanings. The ambiguity of language stems from the lack of any cultural definition of adulthood and how people's lives evolve within it. In the human sciences, too, we have no adequate conception of the nature o f adulthood. We have a detailed picture o f many trees but no view of the forest and no map to guide our journey through it.

I turn now to my own view ofthe life cycle. It derives from my research and draws upon the work of earlier investigators such as Erikson (1950, 1969), Jung, von Franz, Henderson, Jacobi, and Jaffe (1964), Neugarten (1968), Ortega y Gasset (1958), and van Gennep (1960). (For a fuller review, see Levinson & Gooden, 1985.)

Eras: The Macrostructure of the Life Cycle I conceive of the life cycle as a sequence of eras. Each era has its own biopsychosocial character, and each makes its distinctive contribution to the whole. There are major changes in the nature of our lives from one era t o the next, and lesser, though still crucially important, changes within eras. They are partially overlapping: A new era begins as the previous one is approaching its end. A cross- era transition, which generally lasts about five years, ter- minates the outgoing era and initiates the next. The eras and the cross-era transitional periods form the macro- structure of the life cycle, providing an underlying order in the flow of all human lives yet permitting exquisite variations in the individual life course.

Each era and developmental period begins and ends at a well-defined modal age, with a range of about two years above and below this average. The idea of age-linked phases in adult life goes against conventional wisdom. Nevertheless, these age findings have been consistently obtained in the initial research and in subsequent studies. The idea of age-linked eras and periods now has the status of an empirically grounded hypothesis that needs further testing in various cultures.

The first era, Preadulthood, extends from conception to roughly age 22. During these "formative years" the individual grows from highly dependent, undifferentiated infancy through childhood and adolescence to the begin- nings o f a more independent, responsible adult life. It is the era of most rapid biopsychosocial growth. The first few years of life provide a transition into childhood. Dur- ing this time, the neonate becomes biologically and psy- chologically separate from the mother and establishes the initial distinction between the " m e " and the "not m e " - - the first step in a continuing process of individuation.

The years from about 17 to 22 constitute the Early Adult Transition, a developmental period in which preadulthood draws to a close and the era of early adult- hood gets underway. It is thus part of both eras, and not fully a part of either. A new step in individuation is taken as the budding adult modifies her or his relationships

with family and other components of the preadult world and begins to form a place as an adult in the adult world. From a childhood-centered perspective, one can say that development is now largely completed and the child has gained maturity as an adult. The field of developmental (i.e., child) psychology has traditionally taken this view. Taking the perspective of the life cycle as a whole, however, we recognize that the developmental attainments of the first era provide only a base, a starting point from which to begin the next. The Early Adult Transition represents, so to speak, both the full maturity of preadulthood and the infancy of a new era. One is at best off to a shaky start, and new kinds of development are required in the next era.

The second era, early adulthood, lasts from about age 17 to 45 and begins with the Early Adult Transition. It is the adult era of greatest energy and abundance and of greatest contradiction and stress. Biologically, the 20s and 30s are the peak years of the life cycle. In social and psychological terms, early adulthood is the season for forming and pursuing youthful aspirations, establishing a niche in society, raising a family, and as the era ends, reaching a more "senior" position in the adult world. This can be a time of rich satisfaction in terms o f love, sexuality, family life, occupational advancement, creativ- ity, and realization of major life goals. But there can also be crushing stresses. Most of us simultaneously undertake the burdens of parenthood and of forming an occupation. We incur heavy financial obligations when our earning power is still relatively low. We must make crucially im- portant choices regarding marriage, family, work, and life-style before we have the maturity or life experience to choose wisely. Early adulthood is the era in which we are most buffeted by our own passions and ambitions from within and by the demands of family, community, and society from without. Under reasonably favorable conditions, the rewards of living in this era are enormous, but the costs often equal or even exceed the benefits.

The Midlife Transition, from roughly age 40 to 45, brings about the termination of early adulthood and the start of middle adulthood. The distinction between these two eras, and the concept of Midlife Transition as a de- velopmental period that separates and connects them, are among the most controversial aspects o f this schema. The research indicates, however, that the character o f liv- ing always changes appreciably between early and middle adulthood (Holt, 1980; Gooden, 1980; Levinson, 1978, 1984, in press). Similar observations, based on different methods and evidence, are given in the work of Jung, Ortega, Erikson and others, noted earlier. The process of change begins in the Midlife Transition (though the forms and degree of change vary enormously) and continues throughout the era. One developmental task of this tran- sition is to begin a new step in individuation. To the extent that this occurs, we can become more compassionate, more reflective and judicious, less tyrannized by inner conflicts and external demands, and more genuinely lov- ing o f ourselves and others. Without it, our lives become increasingly trivial or stagnant.

January 1986 �9 American Psychologist 5

T h e t h i r d era, middle adulthood, lasts f r o m a b o u t age 40 to 65. D u r i n g this era o u r biological capacities are below those o f early a d u l t h o o d b u t are n o r m a l l y still suf- ficient for an energetic, personally satisfying a n d socially valuable life. Unless o u r lives are h a m p e r e d in some spe- cial way, m o s t o f us d u r i n g o u r 40s and 50s b e c o m e "se- nior m e m b e r s " in o u r own p a r t i c u l a r worlds, however grand or m o d e s t they m a y be. We are responsible n o t only for o u r own work and perhaps the work o f others, b u t also for the d e v e l o p m e n t o f the c u r r e n t generation o f y o u n g adults w h o will soon e n t e r the d o m i n a n t genera- tion.

T h e n e x t era, late adulthood, starts at a b o u t age 60. T h e Late Adult Transition, f r o m 60 to 65, links middle and late a d u l t h o o d and is p a r t o f both. I will n o t discuss late a d u l t h o o d here. M y speculations regarding this era (and a subsequent one, late late a d u l t h o o d ) are given in Levinson (1978).

T h e L i f e S t r u c t u r e a n d I t s Development in Adulthood M y a p p r o a c h to adult d e v e l o p m e n t grows out of, an d is shaped by, the foregoing views regarding the life course a n d the life cycle. I a m p r i m a r i l y interested in appre- hending the n a t u r e o f a person's life at a particular t i m e and the course o f that life over the years. Personality at- tributes, social roles, and biological characteristics are aspects o f a life; they should be regarded as aspects an d placed within the context o f the life.

T h e key c o n c e p t to emerge f r o m m y research is the life structure." the underlying pattern or design o f a person's life at a given time. It is the pillar o f m y c o n c e p t i o n o f adult development. W h e n I speak o f periods in adult de- velopment, I a m referring to periods in the evolution o f the life structure. I will first i n t r o d u c e the c o n c e p t o f life s t r u c t u r e a n d t h e n describe m y t h e o r y and findings a b o u t its evolution in a d u l t h o o d .

T h e m e a n i n g o f this t e r m can be clarified by a co m - parison o f life s t r u c t u r e and personality structure. A the- o r y o f personality s t r u c t u r e is a way o f conceptualizing answers to a c o n c r e t e question: " W h a t kind o f person a m I?" Different theories offer n u m e r o u s ways o f thinking a b o u t this question and o f characterizing oneself or others; for example, in t e r m s o f traits, skills, wishes, conflicts, defenses, or values.

A t h e o r y o f life s t r u c t u r e is a way o f conceptualizing answers to a different question: " W h a t is m y life like n o w ? " As we begin reflecting on this question, m a n y oth- ers c o m e to m i n d . W h a t are the m o s t i m p o r t a n t parts o f m y life, a n d how are t h e y interrelated? W h e r e do I invest m o s t o f m y t i m e a n d energy? Are there some relation- s h i p s - - t o spouse, lover, family, occupation, religion, lei- sure, or w h a t e v e r - - t h a t I would like to m a k e m o r e sat- isfying or meaningful? Are there some things n o t in m y life t h a t I would like to include? Are there interests an d relationships, which now o c c u p y a m i n o r place, t h a t I would like to m a k e m o r e central?

In p o n d e r i n g these questions, we begin to identify those aspects o f the external world that have the greatest

significance to us. We characterize o u r relationship with each o f t h e m and ex am i n e the interweaving o f the various relationships. We find t h at o u r relationships are i m p e r - fectly integrated within a single p a t t e r n o r structure.

T h e p r i m a r y c o m p o n e n t s o f a life s t r u c t u r e are the person's relationships with various others in the external world. T h e o t h er m a y be a person, a group, institution or culture, or a p a r t i c u l a r object o r place. A significant relationship involves an investment o f self (desires, values, c o m m i t m e n t , energy, skill), a reciprocal i n v est m ent b y the other person or entity, an d one o r m o r e social contexts t h at contain the relationship, shaping it an d b e c o m i n g p a r t o f it. Every relationship shows b o t h stability and change as it evolves over time, a n d it has different func- tions in the person's life as the life structure itself changes.

A n individual m ay have significant relationships with m a n y kinds o f others. A significant o t h e r might be an actual person in the individual's c u r r e n t life. We n eed to study interpersonal relationships between friends, lovers, an d spouses; between parents an d t h ei r adult offspring at different ages; between bosses an d subordinates, teachers and students, an d m e n t o r s a n d prot6g6s. A significant other might be a person f r o m the past (e.g., Ezra P o u n d ' s vital relationship with the figure o f D an t e) or a symbolic o r imagined figure f r o m religion, m y t h , fiction, o r private fantasy. T h e o t h er might n o t be an individual b u t might be a collective entity such as a group, institution, o r social m o v e m e n t ; n a t u r e as a whole, o r a p a r t o f n a t u r e such as the ocean, m o u n t a i n s , wildlife, whales in general, or M o b y Dick in particular; o r an object or place such as a farm, a city or country, " a r o o m o f one's own," o r a b o o k o r painting.

T h e c o n c e p t o f life s t r u c t u r e requires us t o e x a m i n e the n a t u r e an d patterning o f an adult's relationships with all significant others a n d the evolution o f these relation- ships over the years. These relationships are the stuff o u r lives are m a d e of. T h e y give shape a n d substance to the life course. T h e y are the vehicle b y which we live o u t - - or b u r y - - v a r i o u s aspects o f o u r selves an d b y which we participate, for b et t er o r worse, in the world a r o u n d us. Students o f the life course seek to d e t e r m i n e the character o f each relationship, its place within the person's evolving life, an d the m e a n i n g o f this life for the person a n d his or her world.

At a n y given time, a life st ru ct u re m a y have m a n y an d diverse c o m p o n e n t s . We found, however, t h a t only o n e or two c o m p o n e n t s - - r a r e l y as m a n y as t h r e e - - o c - cupy a central place in the structure. Mo st often, mar- ri ag e-fam i l y an d o c c u p a t i o n are the central c o m p o n e n t s o f a person's life, although wide variations o c c u r in their relative weight an d in the i m p o r t a n c e o f o t h e r c o m p o - nents. T h e central c o m p o n e n t s are those t h a t have the greatest significance for the self an d the evolving life course. T h e y receive the largest share o f the individual's time and energy, and they strongly influence the character o f the o t h er c o m p o n e n t s . T h e peripheral c o m p o n e n t s are easier to change or detach; t h ey involve less i n v estment o f self an d can be modified with less effect o n the fabric o f the person's life.

6 J a n u a r y 1986 �9 A m e r i c a n Psychologist

In t e r m s o f open systems theory, life structure forms a b o u n d a r y between personality struc t ure a nd social structure and governs the transactions between them. A b o u n d a r y structure is p a r t o f the two adjacent systems it connects, yet is partially separate or a u t o n o m o u s . It can be u n d e r s t o o d only if we see it as a link between them. T h e life structure mediates the relationship between the individual and the e n v i r o n m e n t . It is in pa rt the cause, the vehicle, and the effect o f t ha t relationship. T h e life structure grows out o f the engagement o f the self and the world. Its intrinsic ingredients are aspects o f the self and aspects o f the world, a n d its evolution is shaped by factors in the self and in the world. It requires us to think con- j o i n t l y a b o u t the self a nd the world ra the r t h a n making one p r i m a r y a n d the o t h e r se c onda ry or derivative. A t h e o r y o f life structure must draw equally upon psychol- ogy and the social sciences.

Developmental Periods in Early and Middle Adulthood

In tracing the evolution o f the life st ruc ture in the lives o f m e n a n d women, I have f o u n d an invariant basic pat- tern (with infinite manifest variations): T h e life structure develops t h r o u g h a relatively orderly sequence o f age- linked periods during the adult years. I want to emphasize that this is a finding, not an a priori hypothesis. It was as surprising to m e as to others that the life structure should show such regularity in its adult development, given the absence o f similar regularity in ego development, mor al development, career development, and other specific as- pects o f the life.

T h e sequence consists o f an alternating series o f structure-building a nd structure-changing (transitional) periods. O u r p r i m a r y task in a structure-building period is to f o r m a life struc ture a nd e n h a n c e o u r life within it: We must m a k e certain key choices, f o r m a structure a r o u n d t h e m , and pursue o u r values and goals within this structure. Even when we succeed in creating a structure, life is n o t necessarily tranquil. T h e task o f building a structure is often stressful indeed, and we m a y discover t h a t it is not as satisfactory as we h a d hoped. A structure- building p e r i o d ordinarily lasts 5 to 7 years, 10 at the most. T h e n the life structure tha t has f o r m e d the basis for stability comes into question a nd must be modified.

A transitional period t e rmi na t e s the existing life structure and creates the possibility for a new one. T h e p r i m a r y tasks o f every transitional period are to reap- praise the existing structure, t o explore possibilities for change in the self a nd the world, and to move toward c o m m i t m e n t to the crucial choices that f o r m the basis for a new life structure in the ensuing period. Transitional periods ordinarily last a b o u t five years. Almost half o u r adult lives is spent in developmental transitions. N o life s t r u c t u r e is p e r m a n e n t - - p e r i o d i c change is given in the n a t u r e o f o u r existence.

As a transition comes to an end, one starts making crucial choices, giving t h e m me a ni ng a nd c o m m i t m e n t , and building a life s t ruc ture a r o u n d them. T h e choices are, in a sense, the m a j o r p r o d u c t o f the transition. W h e n all the efforts o f the transition are d o n e - - t h e struggles to

improve work or marriage, to explore alternative possi- bilities o f living, to c o m e m o r e t o t e r m s with the s e l f - - choices must be m a d e and bets mus t be placed. O n e must decide " T h i s I will settle for," a n d start creating a life structure that will serve as a vehicle for the n e x t step in the journey.

Within early and middle adulthood, the develop- mental periods u n f o l d as follows (see Figure 1). We have f ound that each period begins and ends at a well-defined average age; there is a variation o f plus or m i n u s two years a r o u n d the mean. (For a discussion o f the age-link- ages, see Issue 4 below.)

1. T h e Early Adult Transition, f r o m age 17 to 22, is a developmental bridge between preadulthood and early adulthood.

2. T h e Entry Life Structure for Early Adulthood (22 to 28) is the time for building and maintaining an initial m o d e o f adult living.

3. T h e Age 30 Transition (28 to 33) is an oppor tunity to reappraise and modify the entr y structure and to create the basis for the next life structure.

4. T h e Culminating Life Structure for Early Adult- hood (33 to 40) is the vehicle for completing this era and realizing o u r youthf ul aspirations.

5. T h e Midlife Transition (40 to 45) is a n o t h e r o f the great cross-era shifts, serving b o t h to t e r m i n a t e early a d u l t h o o d and to initiate middle adulthood.

6. T h e Entry Life Structure for Middle Adulthood (45 to 50), like its c o u n t e r p a r t above, provides an initial basis for life in a new era.

7. T h e Age 50 Transition (50 to 55) offers a mid- era o p p o r t u n i t y for modifying and perhaps impr oving the entr y life structure.

8. T h e Culminating Life Structure for Middle Adulthood (55 to 60) is the framework in which we con- clude this era.

9. T h e Late Adult Transition (60 to 65) is a b o u n d - ary period between middle and late adulthood, separating and linking the two eras.

T h e first three periods o f early adulthood, f r o m roughly 17 to 33, constitute its " n o v i c e phase." T h e y pro- vide an opportunity to move beyond adolescence, to build a provisional b u t necessarily flawed e n t r y life structure, and to learn the limitations o f that structure. T h e two final periods, f r o m 33 to 45, f o r m the " c u l m i n a t i n g phase," which brings to fruition the efforts o f this era.

A similar sequence exists in middle adulthood. It, too, begins with a novice phase o f three periods, f r o m 40 to 55. T h e Midlife Transition is b o t h an ending and a beginning. In o u r early 40s we are in the full m a t u r i t y o f early a d u l t h o o d and are completing its final chapter; we are also in the infancy o f middle adulthood, jus t beginning to learn a b o u t its promise and its dangers. We r e m a i n novices in every era until we have had a chance to t r y out an e n t r y life s tr uctur e and then to question and m o d - ify it in the mid- er a transition. Only in the per iod o f the Culminating Life Structure, and the cross-era transition that follows, do we reach the conclusion o f that season and begin the shift to the next. D u r i n g the novice phase

J a n u a r y 1986 �9 A m e r i c a n Psychologist 7

Figure 1 Developmental Periods in the Eras of Early and Middle Adulthood

L a t e A d u l t T r a n

Culminating Life Structure for M i d d l e A d u l t h o o d : 55-60

Age 50 Transition: 50-55

Entry Life Structure for M i d d l e A d u l t h o o d : 45-50

M i d - I i f e T r a n s i t i o n: Age 40-45

ERA O f MIDDLE ADULTHOOD: 40-65 Culminating Life Structure for Early A d u l t h o o d : 33-40

Age 30 Transition: 28-33

Entry Life Structure for Early A d u l t h o o d : 22-28

E a r I y A d u I t T a n s i 1 i o n : Age 17-22

ERA O f EARLY ADULTHOOD: 17-45

i 1 i o n : A g e 60-65

ERA OF LATE ADULTHOOD: 60-f

ERA OF PREADULTHOOD: 0-22

Note. This is an expended adaptation of an eadler version that appeared in The Seasons eta Man's Life (p. 57) by D. J. Levtnson with C. N. Derrow, E. B. Klein, M. H. Levinson, and B. McKee, 1978, New York: Alfred A. Knopf, Inc. Copyright 1978 by Alfred A. Knopf, Inc. Adapted by perrnission.

we are, to varying degrees, both excited and terrified by the prospects for living in that era. To varying degrees, likewise, we experience the culminating phase as a time o f rich satisfactions and of bitter disappointments, dis- covering as we so often do that the era ultimately gives us much more and much less than we had envisioned.

This sequence of eras and periods holds for men and women of different cultures, classes, and historical epochs. There are, of course, wide variations in the kinds of life structures people build, the developmental work they do in transitional periods, and the concrete sequence of social roles, events, and personality change. The theory thus provides a general framework of human development within which we can study the profound differences that often exist between classes, genders, and cultures.

The Field of Adult Development: Six Major Issues Like Pirandello's (1964) play, "Six Characters in Search of an Author," the study of adult development might be titled Dozens of Fragments in Search of an Animating Source and a Unifying Plot. The fragments have to do with personality change and development (cognitive,

moral, ego, and the like), occupational career develop- ment, marriage and family development, adult socializa- tion, biological development, adaptation to stress, and more. Diverse studies deal with one or another o f these topics, but they have no evident connection with each other and no clear place in a larger scheme of things.

It is time we asked more seriously, What do we mean by "adult development"? What are the main tasks con- fronting us as we attempt to define and establish it as a field of study? I have attempted to pursue these questions by identifying six fundamental issues. These issues are important to anyone entering this field, whatever the ap- proach. In dealing with the issues, one is taking a position, explicit or implicit, regarding the nature of the field. No position, my own included, has as yet been more than minimally conceptualized and subjected to empirical test.

I will discuss each issue primarily from the vantage point of my own theory and research. To exemplify the diversity of approaches, comparisons will be drawn be- tween life structure theory and other, more or less struc- tural theories of development. These include the structural stage theories of Kegan (1982), Kohlberg (1969, 1973), Loevinger (1976), Piaget (1970) and Werner (1940). Also

8 January 1986 �9 American Psychologist

relevant are personality theories in which the idea o f structure is i m p o r t a n t but is less fully articulated, such as Freud's theory o f psychosexual stages, Jung's (Jung, von Franz, Henderson, Jacobi, & Jaffe, 1964) theory o f adult individuation, and Erikson's (1950) theory o f ego stages.

I will n o t deal here with other, nonstructural ap- proaches. The most c o m m o n o f these is to look for age- linked changes in specific variables. A set o f " a g e curves'" showing regular increase or decrease in certain variables with age m a y be interpreted as evidence for an underlying developmental sequence. This approach tends to be quantitative a n d variable centered a n d to portray devel- o p m e n t as a continuous, incremental process. The struc- turalists, in contrast, emphasize patterns rather than single variables, and they look for a series o f qualitatively (structurally) different stages rather t h a n continuous, quantitative change. The two approaches are not mutually exclusive but are rarely held conjointly. Coming to a more balanced view o f their relative merits is one o f the im- portant issues in the field, but it is beyond the scope o f this article.

The basic structural model, most clearly articulated by Piaget (1970) and held with variations by m a n y de- velopmental theorists, is that development in any d o m a i n involves the evolution o f a structure (cognitive, moral, ego, or whatever), The structure develops through a series o f stages or periods. Structural theorists generally use the t e r m stage. I use the t e r m period, partly to avoid the connotation o f hierarchical progression so c o m m o n in the other theories. W h e n I need a very general term re- ferring to a segment (stage, period, era, or whatever) within a developmental sequence, I speak o f phase. In every structural theory, a phase o f building and main- taining a structure is followed by a phase o f transfor- mation or transition, which leads to the formation o f a qualitatively different structure. One research problem is to identify a sequence o f structures. Another is to un- derstand what happens in a transition: the process by which one structure is transformed into another and the factors that shape this process.

It is n o t m y goal here to examine and evaluate the various theories. All o f t h e m have been useful, and all reflect the rather primitive stage o f psychology as a dis- cipline. All o f us are groping our way in the dark, working with imperfect concepts, methods, and evidence. O u r chief task at this time is n o t to make exaggerated claims b u t to further the growth o f a n infantile discipline. M y intent in identifying the following issues is to provide an analytic basis on which we can compare various ap- proaches, clarify the similarities and differences among them, and consider the state o f this field as a whole.

In question form, the six issues m a y be stated as follows:

1. W h a t are the alternative ways o f defining a struc- tural stage or period?

2. W h a t relative emphasis is given to the structures and structure-building periods or stages, as compared to the transitional, structure-changing periods?

3. How can we make best use o f the distinction be- tween hierarchical levels and seasons o f development?

4. Are there age-linked developmental periods in adulthood?

5. W h a t are the relative merits and limitations o f various research methods?

6. How can we bring together the developmental perspective and the socialization perspective?

Issue 1. W h a t are the alternative ways o f defining a structural stage or period? In the Piagetian tradition, development is a sequence o f stages. Each stage is defined in terms o f the structure that characterizes it. A stage, in this view, is a structure; or to p u t it another way, a stage is a time o f building a n d maintaining a structure. Other developmental theorists, such as Erikson and Freud, de- fined a stage in terms o f its developmental tasks. Thus, Erikson identified each ego stage in terms o f a polarity (trust vs. mistrust, generativity vs. stagnation or exclu- sivity). A person is in a stage when that polarity is o f central importance in experiencing the self and relating to the world. The p r i m a r y developmental tasks o f a stage are to come to terms with both o f its polar opposites and to arrive at some balance or integration o f the poles, so that they are no longer entirely antithetical. One positive outcome o f the developmental work is the formation o f a stage-specific virtue; such as fidelity or caring. However, Erikson did n o t posit a single optimal ego structure as the defining characteristic o f an ego stage. Rather, he de- scribed various kinds o f developmental work on the tasks and various kinds o f developmental achievement or im- pairment that m a y be the products o f the stage.

Like Erikson and Freud, I define each period pri- marily in terms o f its developmental tasks. I a m also con- cerned with the kinds o f life structures that are formed in every structure-building period, and in t h a t sense I a m perhaps more o f a "structuralist" than they. Unlike Piaget, however, I do n o t identify a particular structure as the p r e d o m i n a n t or optimal one for a given period; the life structures generated in any period are infinitely varied.

Issue 2. W h a t relative emphasis is given to the structures and structure-building periods or stages as compared to the transitional, structure-changing periods? Piaget tended to focus mainly on the sequence o f struc- tures. W h e n he spoke o f a stage, he m e a n t a structure. His successive stages in cognitive development f o r m a hierarchical series o f cognitive levels or structures. Al- though recognizing that transitions are required for the shift from one structure to another, he did n o t study the transitional process. He treated the transitions as lacunae or zones o f ambiguity between the structures, rather t h a n as stages in their own right, possessing a distinctive char- acter o f their own. By a n d large, Piaget studied the struc- tures rather than the course o f development as a con- tinuing evolution.

In contrast, there is now a growing body o f research on transitions; for example, periods o f change and read- j u s t m e n t following a major life event such as marriage, divorce, the birth o f a child, retirement, or the loss o f a loved one (Hareven & Adams, 1982; Lowenthal, T h u r n -

J a n u a r y 1986 �9 American Psychologist 9

her, & Chiriboga, 1975). In this work, the focus on the process o f change is often so strong that little attention is given to the states (structures) that precede and follow it. A transition is a shift from state A to state B; it is as important to study A and B as it is to study the intervening process o f change. M u c h o f the recent theory and research on transitions is centered narrowly on adaptation and change s t e m m i n g from a single event. This work con- tributes to our knowledge o f events and adaptations, but it is generally not based on a theory o f adult development, and it cannot, in itself, generate a theory o f adult devel- o p m e n t (Levinson, 1980).

In studying the development o f the life structure, I give equal weight to the structure-building periods and the structure-changing periods. Adults spend almost as m u c h time in the latter as in the former, and both play a crucial part in adult development. To those who focus chiefly on structures, I would emphasize the importance o f the transitional, structure-changing periods. A n d to those who deal primarily with transitions, I would em- phasize that a crucially important feature o f any transition is the new structure emerging from it. I a m equally con- cerned with the life structures people form at different ages and with the transitions that lead from one life struc- ture to another. I study the sequence by which individuals build, live within, modify, and rebuild the life structure over a span o f m a n y years. The standard methods o f cross- sectional and longitudinal research are not adequate for this task. We must develop biographical methods that more fully capture the flow o f the life course (see Issue 5, below).

Issue 3. How can we make best use o f the distinc- tion between hierarchical levels and seasons o f develop- ment? In the Piagetian approach, the successive stages form a hierarchical progression from lower to higher on a developmental scale. Stage 3 is developmentally more advanced t h a n stage 2, and less advanced t h a n stage 4. In other theories, such as Freud's, Erikson's, and mine, the phases have more o f the character o f seasons. Phase 3 comes after phase 2 and to some extent builds upon it, b u t phase 3 is not necessarily more "advanced." Each phase has its own intrinsic value, appropriate to its place in the life cycle. The sequence o f phases is seen within the framework o f the life cycle rather t h a n as a temporal order governed solely by its own internal logic.

This issue is o f fundamental importance in the study o f adult development. The imagery o f a hierarchy o f de- velopmental stages is prevalent in the study o f childhood, where development takes primarily the form o f positive growth. There are generally agreed-upon criteria for judg- ing that one stage represents a "higher level" than another in preadulthood, where we make such dramatic advances in body shape and size, cognitive complexity, adaptive capability, and character formation. The variables that show such rapid growth until age 20 or so tend to stabilize in early a d u l t h o o d and then gradually decline over the course o f middle and late adulthood. At the same time, other psychosocial qualities may develop to greater ma- t u r i t y in middle a n d late adulthood.

It is essential to keep in m i n d that development is not s y n o n y m o u s with growth. Rather, it has the twin as- pects o f "growing u p " and "growing down." Perhaps the best term for the former is adolescing, which means mov- ing toward adulthood, and for the latter, senescing, which means moving toward old age and dissolution. The bal- ance o f the two varies from era to era.

In preadulthood we are mostly, though n o t only, adolescing. In late a d u l t h o o d we are mostly senescing, though there is some vitally i m p o r t a n t adolescing to be done as we come to the culmination o f the entire life cycle and a t t e m p t to give fuller meaning to our own lives, to life and death as ultimate states, and to the condition o f being h u m a n . At the end o f the life cycle, as we engage in the final process o f biological senescing, we are also engaged in the final work o f psychosocial adolescing, o f growing up to our full adulthood. It is a costly oversim- plification to equate childhood with growth and old age with decline.

In early and middle adulthood, adolescing a n d se- nescing coexist in an uneasy balance. Biologically, the forces o f senescence come to equal and then gradually to exceed those o f adolescence. Psychosocially, there are possibilities for further growth, b u t they are by no means assured o f realization and they are jeopardized by external constraints as well as inner vulnerabilities. We must deal with this coexistence o f growth and decline in our own lives and in our research on adult development. Simple models o f growth do n o t hold in adulthood. It is inap- propriate to study adult development with childhood- centered models. Adulthood has its own distinctive char- acter and must be studied in its own right, not merely as an extrapolation from childhood. Erikson warned us o f this long ago, and Jung even earlier, b u t it is a hard lesson to learn.

In studying the development o f the life structure, we are not yet wise enough about life to say with precision that one life structure is developmentally higher, or more advanced, t h a n another. We still know very little about the complexities and contradictions o f the h u m a n life course. When we have learned much more about the kinds o f life structures people build at different ages, under dif- ferent conditions, we may be more able to evaluate, con- ceptualize, and measure the variations in developmental level among life structures.

It is clearly unrealistic to assume that a person's cul- minating life structure for early adulthood (in the 30s) will necessarily be more advanced developmentally t h a n the preceding entry life structure (in the 20s). A n d when we compare the culminating life structure for early adult- hood with the entry life structure for middle adulthood, we have to take account o f the change in eras, which presents new possibilities and new burdens. The great challenge now, as we go about establishing this field, is to observe and describe the individual life course as richly as possible and to generate concepts that represent its underlying complexity, order, and chaos.

Taking a small step toward evaluation, I have been developing the concept o f the satisfactoriness o f the life

10 J a n u a r y 1986 �9 American Psychologist

structure (Levinson, 1978). Like m a n y o f m y concepts, this one has both an external and an internal reference. Externally, it refers to the viability o f the life structure in the external w o r l d - - h o w well it works and what it pro- vides in the way o f advantages and disadvantages, suc- cesses a n d failures, rewards and deprivations. Internally, it refers to the suitability o f the life structure for the self. The key questions here are the following: W h a t aspects o f the self can be lived out within this structure? W h a t aspects must be neglected or suppressed? W h a t are the benefits and costs o f this structure for the self?.

Satisfactoriness o f the life structure is n o t the same as "level o f adjustment," "sense o f well being," or "life satisfaction" as these are usually assessed in questionnaire or brief interview studies. Some people feel quite satisfied with lives t h a t are reasonably comfortable and orderly but in which they have m i n i m a l engagement or sense o f purpose. Their lives have m u c h viability in the world b u t little suitability for the self. W h e n the self is so little in- vested in the life, the life in t u r n can offer little to the s e l f - - t h o u g h m a n y adults settle for this condition. Like- wise, people who are passionately engaged in living, and who invest the self freely in the life structure, m a y ex- perience m u c h t u r m o i l and suffering. They ask more o f life t h a n it can readily provide. The intense engagement in life yields more a b u n d a n t fruits b u t exacts a different and in some ways greater toll.

Assessing the satisfactoriness o f the life structure is thus a complex matter. We c a n n o t do it by means o f a few behavioral criteria or questionnaire items. Moreover, the basis for assessment must be different in different sea- sons o f life. The range o f possibilities in building an entry life structure for early a d u l t h o o d is m u c h different from that in, say, the culminating life structure for middle adulthood.

It is i m p o r t a n t also to distinguish between the de- velopment o f the life structure and the development o f the self during the adult years. Psychologists who have strong intellectual origins in the study o f childhood tend to think o f development as growth in various aspects o f the self, such as cognition, morality, and ego functions. The study o f adulthood, and especially o f life structure development, takes us beyond the focus on the self: It requires us to examine the life course in its complexity, to take into account the external world as well as the self, to study the engagement o f the self in the world, and to move beyond an encapsulated view o f the self. As we learn more about the lived life and the evolution o f the life structure, we will have a sounder basis for studying the adult development o f the self.

Issue 4. Are there age-linked developmental periods in adulthood? The discovery o f age-linked periods in the adult development o f the life structure is one o f the most controversial findings o f m y research. The most c o m m o n response among psychologists a n d social scientists is in- credulity. It is simply not possible, they aver, that devel- o p m e n t should unfold in so orderly a sequence during a d u l t h o o d - - a standard series o f periods, each beginning at a well-defined modal age with a range o f only four or

five years a r o u n d it. They note that the available evidence goes against the hypothesis o f age-linked stages in adult personality development. Moreover, social roles a n d ca- reers evolve in accord with institutionally defined time- tables that vary widely among institutions a n d cultures. Those who regard a d u l t h o o d as a series o f major life events (such as marriage, loss, and retirement) that m a y bring about changes in individual adaptation or person- ality, and who have no conception o f adult development as a source o f order in the life course, m a i n t a i n that these life events occur at widely varying ages and thus make impossible the kind o f temporal order I have found.

I have replied (1978, 1980, 1981) to these objections on both theoretical a n d empirical grounds. I agree t h a t neither individual personality nor social roles evolve through a standard sequence o f age-linked stages in adulthood. The only investigator who posited such a se- quence o f personality stages was G o u l d (1978), b u t his hypothesis awaits further testing. Erikson (1950) and Vaillant (1977) proposed a sequence o f ego stages b u t were less specific about the age linkages. I agree, further, that major life events occur at varying ages. The study o f events does n o t in itself provide a basis for a theory o f adult development. It is abundantly evident that, at the level o f events, roles, or personality, individual lives unfold in m y r i a d ways. I make no claim for order in the concrete individual life course; indeed, I believe that there is m u c h more diversity and disorder t h a n most researchers have been able to see, through their narrow theoretical lenses and methodological constraints.

I do propose, however, that there is an underlying order in the h u m a n life course, an order shaped by the eras a n d by the periods in life structure development. Personality, social structure, culture, social roles, major life events, biology--these and other influences exert a powerful effect on the actual character o f the individual life structure at a given time and on its development dur- ing adulthood. It is m y hypothesis, however, that the basic nature and timing o f life structure development are given in the life cycle at this time in h u m a n evolution.

As I have emphasized from the start, I offer this viewpoint as a tentative, empirically grounded hypothesis, n o t as a fully demonstrated truth. I did n o t have it in m i n d when I started m y research on the adult develop- ment o f men. The concept o f life structure emerged slowly during the first years o f that research. The discovery o f a sequence o f alternating, age-linked structure-building and transitional periods came even more slowly. T h a t se- quence has been found in the intensive study o f m a n y lives: the accounts o f the 40 m e n interviewed in m y first study (1978) and the 45 women interviewed in m y current study (Levinson, in press); the accounts o f over 100 m e n and women, from different countries and historical pe- riods, whose lives have been sufficiently portrayed in bi- ographies, autobiographies, novels, and plays; a study o f women's lives into their 30s by Stewart (1976); a study o f Black m e n by G o o d e n (1980); biographical studies o f Jung (Holt, 1980) and ofWilli Brandt (Kellerman, 1975); a pilot sample o f 30 to 40 m e n and women interviewed

J a n u a r y 1986 �9 American Psychologist 11

for my forthcoming project on middle adulthood; and accounts of the life cycle written over 2,000 years ago by Confucius, Solon, and the authors of the Talmud (Lev- inson, 1978). I know of no systematic evidence discon- firming the hypothesis. As new evidence comes in, the theory will, no doubt, be modified, amplified, and made more complex.

The hypothesis of age-linked periods in life structure development is thus well grounded in empirical evidence, though not in quantitative, large-sample research. To say that it " m u s t " be wrong, that it "doesn't make sense," is simply to say that it violates the conventional wisdom or the assumptions of other theories. We cannot confirm or disconfirm a theory of life structure by studying changes in personality, social role, moral functioning, or the like. Such a theory can be tested adequately only by intensive studies of the individual life course, through which we follow the evolution of the life structure over a span of years.

Issue 5. What are the relative merits and limitations of various research methods? The favored methods in developmental research have traditionally been the cross- sectional and the longitudinal. Cross-sectional research is the most efficient and manageable, but it has severe limitations as a means of exploring the process o f devel- opment.

Longitudinal research has the great advantage of en- abling us to study a sample over a span of years, but it has major disadvantages as well. The initial concepts and methods may become outmoded after a few years, but the method requires administration of the same measures at periodic intervals over the course of at least several adult years. The measures may have different meanings and validities at one point in history than at others. This is a particular difficulty in research on adult development. Longitudinal research ordinarily involves massive testing and interviewing at intervals of 1 to 10 or more years. The sample means are then used to plot continuous age curves, which may represent developmental sequences. This method is at its best when we have well-identified variables that stem directly from developmentally im- portant concepts and for which we have measures of es- tablished reliability and validity. We are far from this ideal in the field of adult development. Even when interesting age curves are found, we are often uncertain about the validity of the measures, the significance of the variables, and the theory of development for which the findings are relevant. A premature emphasis on quantification often keeps us from exploring the phenomena under study and from generating powerful concepts from which appro- priate measures can be derived.

The biographical method is an effort to reconstruct the life course by interviewing the person and by using various other sources, much as the biographer does in writing a book-length life story. Like the cross-sectional and longitudinal methods, it is not a single entity but a broad approach, with many variations in research design, techniques, and aims. It, too, has inherent limitations, especially in its reliance on memory and reconstruction.

It is not ideal for all purposes and to the exclusion o f other methods. Still, it has certain advantages and ought to be recovered from the limbo to which psychology has for so long relegated it. For the study of life structure development, we have no other method of comparable value. The biographical method is the only one that en- ables us to obtain a complex picture of the life structure at a given time and to delineate the evolution of the life structure over a span of years. It is well suited for gaining a more concrete sense of the individual life course, for generating new concepts, and in time, for developing new variables, measures, and hypotheses that are rooted in theory and are relevant to life as it actually evolves.

lssue 6. How can we bring together the developmental perspective and the socialization perspective? Different theories deal with different variables or domains, yet the differences are often blurred or ignored. By and large, psychologists study the development of properties of the personmcognition, morality, ego, attitudes, interests, or psychodynamics. When we find a basic order in the evo- lution of these properties, the order is assumed to have its origins in the nature of the organism. External con- ditions influence the specific forms of individual growth and decline and serve to facilitate or hinder the process, but the basic developmental scheme is considered organ- ismically given. Indeed, a developmental perspective in psychology has traditionally meant the search for a mat- urationally built-in, epigenetic, preprogrammed se- quence.

The social sciences, on the other hand, look pri- marily to the sociocultural world for the sources of order in the life course. They show how culturally defined age grades, institutional timetables, and systems o f accultur- ation and socialization shape the sequence of our lives. What we may broadly term the socialization perspective (Clausen, 1972; Hareven & Adams, 1982; Lowenthal et al., 1975; Neugarten, 1968 ) holds that the timing of life events and the evolution of adult careers in occupation, family, and other institutions is determined chiefly by forces in the external world; forces in the individual bi- ology or psyche produce minor variance around the ex- ternally determined norms. A balanced approach to the search for order in the life course would obviously draw jointly upon the perspectives of development and social- ization. Yet this integration has rarely been attempted.

What about the evolution of the life structure? Is it determined primarily from within or from without? Is it a product more of development or of socialization? As I have already indicated, the life structure constitutes a b o u n d a r y u a mediating zone between personality struc- ture and social structure. It contains aspects o f both and governs the transactions between them. The life structure is a pattern of relationships between the self and the world. It has an inner-psychological aspect and an external-so- cial aspect. The universal sequence of periods in the evo- lution of the life structure has its origins in the psycho- biological properties of the human species, as well as in the general nature of human society at this phase of its evolution (Levinson, 1978, Ch. 20). Each individual life

12 January 1986 �9 American Psychologist

s t r u c t u r e p r o g r e s s e s t h r o u g h t h e s u c c e s s i v e p e r i o d s i n i t s o w n u n i q u e way, i n f l u e n c e d b y a m u l t i p l i c i t y o f s p e c i f i c b i o l o g i c a l , p s y c h o l o g i c a l , a n d s o c i a l c o n d i t i o n s .

B e c a u s e t h e life s t r u c t u r e is n o t s o l e l y a p r o p e r t y o f t h e i n d i v i d u a l , i t s e v o l u t i o n c a n n o t b e u n d e r s t o o d s o l e l y f r o m a n i n t r a o r g a n i s m i c , d e v e l o p m e n t a l p e r s p e c t i v e . Be- c a u s e t h e life s t r u c t u r e is n o t s i m p l y a m a t t e r o f e x t e r n a l l y i m p o s e d e v e n t s a n d r o l e s , its e v o l u t i o n c a n n o t b e u n d e r - s t o o d s i m p l y f r o m a s o c i a l i z a t i o n p e r s p e c t i v e . I t is n e e - essary, i n s t e a d , t o c r e a t e a n e w p e r s p e c t i v e t h a t c o m b i n e s d e v e l o p m e n t a n d s o c i a l i z a t i o n a n d t h a t d r a w s e q u a l l y o n b i o l o g y , p s y c h o l o g y , a n d s o c i a l s c i e n c e , a s w e l l a s o n t h e h u m a n i t i e s . M o v e m e n t i n t h i s d i r e c t i o n is n o t easy, vi- o l a t i n g a s i t d o e s t h e c u r r e n t v e s t e d i n t e r e s t s o f e a c h d i s - c i p l i n e i n v o l v e d . F o r t u n a t e l y , i t is b e c o m i n g i n c r e a s i n g l y e v i d e n t t h a t t h e s h a r p d i v i s i o n s a m o n g t h e s e d i s c i p l i n e s , w h a t e v e r t h e i r v a l u e i n t h e p a s t , a r e n o w v e r y costly. N e w c r o s s - d i s c i p l i n a r y b o u n d a r y s y s t e m s m u s t b e g e n e r a t e d i f w e a r e t o p r o g r e s s i n t h e s t u d y o f b a s i c i n d i v i d u a l a n d s o c i a l p h e n o m e n a - - n o t t h e l e a s t o f w h i c h is t h e h u m a n life c o u r s e . T h e s t u d y o f t h e life s t r u c t u r e a n d its d e v e l - o p m e n t is a n e f f o r t i n t h i s d i r e c t i o n .

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