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Life Cycle

Life Cycle

The eight stages of life



The observer of life is always immersed in it and thus unable to transcend the limited perspectives of his stage and condition. Religious world views usually evolve pervasive configurations of the course of life: one religion may envisage it as a continuous spiral of rebirths, another as a cross-roads to damnation or salvation. Various “ways of life” harbor more or less explicit images of life’s course: a leisurely one may see it as ascending and descending steps with a comfortable platform of maturity in between; a competitive one may envision it as a race for spectacular success—and sudden oblivion. The scientist, on the other hand, looks at the organism as it moves from birth to death and, in the larger sense, at the individual in a genetic chain; or he looks at the cultural design of life’s course as marked by rites of transition at selected turning points.

The very choice of the configuration “cycle of life,” then, necessitates a statement of the writer’s conceptual ancestry—clinical psychoanalysis. The clinical worker cannot escape combining knowledge, experience, and conviction in a conception of the course of life and of the sequence of generations—for how, otherwise, could he offer interpretation and guidance? The very existence of a variety of psychiatric “schools” is probably due to the fact that clinical practice and theory are called upon to provide a total orientation beyond possible verification.

Freud confessed only to a scientific world view, but he could not avoid the attitudes (often in contradiction to his personal values) that were part of his times. The original data of psychoanalysis, for example, were minute reconstructions of “pathogenic” events in early childhood. They supported an orientation which—in analogy to teleology— could be called originology, i.e., a systematic attempt to derive complex meanings from vague beginnings and obscure causes. The result was often an implicit fatalism, although counteracted by strenuously “positive” orientations. Any theory em-bracing both life history and case history, however, must find a balance between the “backward” view of the genetic reconstruction and the “forward” formulation of progressive differentiation in growth and development; between the “downward” view into the depth of the unconscious and the “upward” awareness of compelling social experience; and between the “inward” exploration of inner reality and the “outward” attention to historical actuality.

This article will attempt to make explicit those psychosocial insights that often remain implicit in clinical practice and theory. These concern the individual, who in principle develops according to predetermined steps of readiness that enable him to participate in ever more differentiated ways along a widening social radius, and the social organization, which in principle tends to invite such developmental potentialities and to support the proper rate and the proper sequence of their unfolding.

“Cycle” is intended to convey the double tendency of individual life to “round itself out” as a coherent experience and at the same time to form a link in the chain of generations from which it receives and to which it contributes both strength and weakness.

Strategic in this interplay are developmental crises—“crisis” here connoting not a threat of catastrophe but a turning point, a crucial period of increased vulnerability and heightened potential, and, therefore, the ontogenetic source of generational strength and maladjustment.

The eight stages of life

Man’s protracted childhood must be provided with the psychosocial protection and stimulation which, like a second womb, permits the child to develop in distinct steps as he unifies his separate capacities. In each stage, we assume a new driveand-need constellation, an expanded radius of potential social interaction, and social institutions created to receive the growing individual within traditional patterns. To provide an evolutionary rationale for this (for prolonged childhood and social institutions must have evolved together), two basic differences between animal and man must be considered.

We are, in Ernst Mayr’s terms (1964), the “generalist” animal, prepared to adapt to and to develop cultures in the most varied environments. A long childhood must prepare the newborn of the species to become specialized as a member of a pseudo species (Erikson 1965), i.e., in tribes, cultures, castes, etc., each of which behaves as if it were the only genuine realization of man as the heavens planned and created him. Furthermore, man’s drives are characterized by instinctual energies, which are, in contrast to other animals, much less bound to instinctive patterns (or inborn release mechanisms). A maximum of free instinctual energy thus remains ready to be invested in basic psychosocial encounters which tend to fix developing energies into cultural patterns of mutuality, reliability, and competence. Freud has shown the extent to which maladaptive anxiety and rage accompany man’s instinctuality, while postulating

Figure 1Psychosocial crises in the life cycle

Source: Adapted from Childhood and Society, by Erik H. Erikson, Copyright 1950, © 1963 by W. W. Norton & Company. Reproduced with permission of W. W. Norton & Company, Inc. and Hogarth Press, Ltd.

the strength of the ego in its defensive and in its adaptive aspects (see Freud 1936; Hartmann 1939). We can attempt to show a systematic relationship between man’s maladjustments and those basic strengths which must emerge in each life cycle and re-emerge from generation to generation (Erikson 1964).

In Figure 1, above, the various psychosocial crises and thus the ontogenetic sources of adaptation and of maladjustment are arranged according to the epi gene tic principle. The diagonal signifies a successive development and a hierarchic differentiation of psychosocial strengths.

If a favorable ratio of basic trust over basic mistrust is the first step in psychosocial adaptation, and the second step a favorable ratio of autonomy over shame and doubt, the diagram indicates a number of fundamental facts. Each basic psycho-social trend (1, 2, etc.) meets a crisis (I, 1; II, 2; etc.) during a corresponding stage (I, II, etc.), while all must exist from the beginning in some form (broken line) and in later stages (solid lines) must continue to be differentiated and reintegrated with newly dominant trends. An infant will show something like autonomy from the time of birth (I, 2), but it is not until the second year (II, 2) that he is ready to experience and to manage the critical conflict of becoming an autonomous creature while continuing to be dependent. At this time those around him will convey to him a cultural and personal version of the ratio of autonomy and dependence. The diagonal thus indicates a necessary sequence of such encounters but leaves room for variations in tempo and intensity.

The epi genetic pattern will have to be kept in mind as we now state for each stage: (a) the psychosocial crisis evoked by social interaction, which is in turn facilitated and necessitated by newly developing drives and capacities, and the specific psychosocial strength emanating from the solution of this crisis; (fc) the specific sense of estrangement awakened at each stage and its connection with some major form of psychopathology;(c) the special relationship between all of these factors and certain basic social institutions (Erikson 1950).

Infancy (basic trust versus mistrust—hope)

The resolution of the first psychosocial crisis is performed primarily by maternal care. The newborn infant’s more or less coordinated readiness to in-

corporate by mouth and through the senses meets the mother’s and the society’s more or less coordinated readiness to feed him and to stimulate his awareness. The mother must represent to the child an almost somatic conviction that she (his first “world”) is trustworthy enough to satisfy and to regulate his needs. But the infant’s demeanor also inspires hope in adults and makes them wish to give hope; it awakens in them a strength which they, in turn, are ready and needful to have confirmed in the experience of care. This is the on togenetic basis of hope, that first and basic strength which gives man a semblance of instinctive certainty in his social ecology.

Unavoidable pain and delay of satisfaction, however, and inexorable weaning make this stage also prototypical for a sense of abandonment and helpless rage. This is the first of the human estrangements against which hope must maintain itself throughout life.

In psychopathology, a defect in basic trust can be evident in early malignant disturbances or can become apparent later in severe addictionor in habitual or sudden withdrawal into psychotic states.

Biological motherhood needs at least three links with social experience—the mother’s past experience of being mothered, a method of care in trust-worthy surroundings, and some convincing image of providence. The infant’s hope, in turn, is one cornerstone of the adult’s faith, which throughout history has sought an institutional safeguard in organized religion. However, where religious institutions fail to give ritual actuality to their formulas they may become irrelevant to psychosocial strength.

Hope , then, is the first psychosocial strength. It is the enduring belief in the attainability of primal wishes in spite of the anarchic urges and rages of dependency.

Early childhood (autonomy versus shame, doubt —will power)

Early childhood sets the stage for psychosocial autonomy by rapid gains in muscular maturation, locomotion, verbalization, and discrimination. All of these, however, create limits in the form of spatial restrictions and of categorical divisions between “yes and no,” “good and bad,” “right and wrong,” and “yours and mine.” Muscular matu-ration sets the stage for an ambivalent set of social modalities—holding on and letting go. To hold on can become a destructive retaining or restraining, or a pattern of care—to have and to hold. To let go, too, can turn into an inimical letting loose, or a relaxed “letting pass” and “letting be.” Freud calls this the anal stage of libido development be-cause of the pleasure experienced in and the conflict evoked over excretory retention and elimination.

This stage, therefore, becomes decisive for the ratio of good will and willfulness. A sense of self-control without loss of self-esteem is the ontogenetic source of confidence in free will; a sense of overcontrol and loss of self-control can give rise to a lasting propensity for doubt and shame. The matter is complicated by the different needs and capacities of siblings of different ages—and by their rivalry.

Shame is the estrangement of being exposed and conscious of being looked at disapprovingly, of wishing to “bury one’s face” or “sink into the ground.” This potentiality is exploited in the “shaming” used throughout life by some cultures and causing, on occasion, suicide. While shame is related to the consciousness of being upright and exposed, doubt has much to do with the consciousness of having a front and a back (and of the vulnerability of being seen and influenced from behind). It is the estrangement of being unsure of one’s will and of those who would dominate it.

From this stage emerges the propensity for compulsive overcompliance or impulsive defiance. If denied a gradual increase in autonomy of choice the individual may become obsessed by repetitiveness and develop an overly cruel conscience. Early self-doubt and doubt of others may later find their most malignant expression in compulsion neuroses or in paranoiac apprehension of hidden critics and secret persecutors threatening from behind.

We have related basic trust to the institutions of religion. The enduring need of the individual to have an area of free choice reaffirmed and delineated by formulated privileges and limitations, obligations and rights, has an institutional safeguard in the principles of law and order and of justice. Where this is impaired, however, the law itself is in danger of becoming arbitrary or formalistic, i.e., “impulsive” or “compulsive” itself.

Will power is the unbroken determination to exercise free choice as well as self-restraint in spite of the unavoidable experience of shame, doubt, and a certain rage over being controlled by others. Good will is rooted in the judiciousness of parents guided by their respect for the spirit of the law.

Play age (initiative versus guilt—purpose)

Able to move independently and vigorously, the child, now in his third or fourth year, begins to comprehend his expected role in the adult world and to play out roles worth imitating. He develops a sense of initiative. He associates with age-mates and older children as he watches and enters into games in the barnyard, on the street corner, or in the nursery. His learning now is intrusive; it leads him into ever new facts and activities, and he becomes acutely aware of differences between the sexes. But if it seems that the child spends on his play a purposefulness out of proportion to “real” purposes, we must recognize the human necessity to simultaneously bind together infantile wish and limited skill, symbol and fact, inner and outer world, a selectively remembered past and a vaguely anticipated future—all before adult “reality” takes over in sanctioned roles and adjusted purposes.

The fate of infantile genitality remains determined by the sex roles cultivated and integrated in the family. In the boy, the sexual orientation is dominated by phallic-intrusive initiative; in the girl, by inclusive modes of attractiveness and “motherliness.”

Conscience, however, forever divides the child within himself by establishing an inner voice of self-observation, self-guidance, and self-punishment. The estrangement of this stage, therefore, is a sense of guilt over goals contemplated and acts done, initiated, or merely fantasied. For initiative includes competition with those of superior equipment. In a final contest for a favored position with the mother, “oedipal” feelings are aroused in the boy, and there appears to be an intensified fear of finding the genitals harmed as punishment for the fantasies attached to their excitability.

Infantile guilt leads to the conflict between unbounded initiative and repression or inhibition. In adult pathology this residual conflict is expressed in hysterical denial, general inhibition, and sexual impotence, or in overcompensatory exhibitionism and psychopathic acting-out.

The word “initiative” has for many a specifically American, or “entrepreneur,” connotation. Yet man needs this sense of initiative for whatever he learns and does, from fruit gathering to commercial enterprise—or the study of books.

The play age relies on the existence of some form of basic family, which also teaches the child by patient example where play ends and irreversible purpose begins. Only thus are guilt feelings inte-grated in a strong (not severe) conscience; only thus is language verified as a shared actuality. The “oedipal” stage thus not only results in a moral sense restricting the horizon of the permissible, but it also directs the way to the possible and the tangible, which attract infantile dreams to the goals of technology and culture. Social institutions, in turn, offer an ethos of action, in the form of ideal adults fascinating enough to replace the heroes of the picture book and fairy tale.

That the adult begins as a playing child means that there is a residue of play acting and role playing even in what he considers his highest purposes. These he projects on a larger and more perfect historical future; these he dramatizes in the ceremonial present with uniformed players in ritual arrangements; thus men sanction aggressive initiative, even as they assuage guilt by submission to. a higher authority.

Purpose, then, is the courage to envisage and pursue valued and tangible goals guided by con-science but not paralyzed by guilt and by the fear of punishment.

School age (industry versus inferiority—competence)

Before the child, psychologically a rudimentary parent, can become a biological parent, he must begin to be a worker and potential provider. Genital maturation is postponed (the period of latency). The child develops a sense of industriousness, i.e., he begins to comprehend the tool world of his culture, and he can become an eager and absorbed member of that productive situation called “school,” which gradually supersedes the whims of play. In all cultures, at this stage, children receive systematic instruction of some kind and learn eagerly from older children.

The danger of this stage lies in the development of a sense of inadequacy. If the child despairs of his skill or his status among his tool partners, he may be discouraged from further learning. He may regress to the hopeless rivalry of the oedipal situation. It is at this point that the larger society becomes significant to the child by admitting him to roles preparatory to the actuality of technology and economy. Where he finds, however, that the color of his skin or the background of his parents rather than his wish and his will to learn will decide his worth as an apprentice, the human propensity for feeling unworthy (inferior) may be fatefully aggravated as a determinant of character development.

But there is another danger: If the overly conforming child accepts work as the only criterion of worthwhileness, sacrificing too readily his imagination and playfulness, he may become ready to submit to what Marx called a “craft-idiocy,” i.e., become a slave of his technology and of its established role typology.

This is socially a most decisive stage, preparing the child for a hierarchy of learning experiences which he will undergo with the help of cooperative peers and instructive adults. Since industriousness involves doing things beside and with others, a first sense of the division of labor and of differential opportunity—that is, a sense of the technological ethos of a culture—develops at this time. Therefore, the configurations of cultural thought and the manipulations basic to the prevailing technology must reach meaningfully into school life.

Competence, then, is the free exercise (unim-paired by an infantile sense of inferiority) of dex-terity and intelligence in the completion of serious tasks. It is the basis for cooperative participation in some segment of the culture.

Adolescence (identity versus identity confusion— fidelity)

With a good initial relationship to skills and tools, and with the advent of puberty, child-hood proper comes to an end. The rapidly growing youths, faced with the inner revolution of puberty and with as yet intangible adult tasks, are now primarily concerned with their psychosocial identity and with fitting their rudimentary gifts and skills to the occupational prototypes of the culture.

The integration of an identity is more than the sum of childhood identifications. It is the accrued confidence that the inner sameness and continuity gathered over the past years of development are matched by the sameness and continuity in one’s meaning for others, as evidenced in the tangible promise of careers and life styles.

The adolescent’s regressive and yet powerful impulsiveness alternating with compulsive restraint is well known. In all of this, however, an ideological seeking after an inner coherence and a durable set of values can be detected. The particular strength sought is fidelity—that is, the opportunity to fulfill personal potentialities (including erotic vitality or its sublimation) in a context which permits the young person to be true to himself and true to significant others.“Falling in love” also can be an attempt to arrive at a self-definition by seeing oneself reflected anew in an idealized as well as eroticized other.

From this stage on, acute maladjustments due to social anomie may lead to psychopathological regressions. Where role confusion joins a hopelessness of long standing, borderline psychotic episodes are not uncommon.

Adolescents, on the other hand, help one another temporarily through much regressive insecurity by forming cliques and by stereotyping themselves, their ideals, and their “enemies.” In this they can be clannish and cruel in their exclusion of all those who are “different.” Where they turn this repudiation totally against the society, delinquency may be a temporary or lasting result.

As social systems enter into the fiber of each succeeding generation, they also absorb into their lifeblood the rejuvenative power of youth. Adolescence is thus a vital regenerator in the process of social evolution, for youth can offer its loyalties and energies to the conservation of that which it feels is valid as well as to the revolutionary correction of that which has lost its regenerative significance.

Adolescence is least “stormy” among those youths who are gifted and well trained in the pursuit of productive technological trends. In times of unrest, the adolescent mind becomes an ideological mind in search of an inspiring unification of ideas. Youth needs to be affirmed by peers and confirmed by teachings, creeds, and ideologies which express the promise that the best people will come to rule and that rule will develop the best in people. A society’s ideological weakness, in turn, expresses itself in weak utopianism and in widespread identity con-fusion.

Fidelity, then, is the ability to sustain loyalties freely pledged in spite of the inevitable contradictions of value systems. It is the cornerstone of identity and receives inspiration from confirming ideologies and “ways of life.”

Young adulthood (intimacy versus isolation— love)

Consolidated identity permits the self-abandonment demanded by intimate affiliations, by passionate sexual unions, or by inspiring encounters. The young adult is ready for intimacy and solidarity—that is, he can commit himself to affiliations and partnerships even though they may call for significant sacrifices and compromises. Ethical strength emerges as a further differentiation of ideological conviction (adolescence) and a sense of moral obligation (childhood).

True genital maturity is first reached at this stage; much of the individual’s previous sex life is of the identity-confirming kind. Freud, when asked for the criteria of a mature person, is reported to have answered:“Lieben und Arbeiten” (“love and work”). All three words deserve equal emphasis.

It is only at this stage that the biological differences between the sexes result in a full polarization within a joint life style. Previously established strengths have helped the two sexes to converge in capacities and values which enhance communication and cooperation, while divergence is now of the essence in love life and in procreation. Thus the sexes first become similar in consciousness, language, and ethics in order then to be maturely different. But this, by necessity, causes ambivalences.

The danger of this stage is possible psychosocial isolation—that is, the avoidance of contacts which commit to intimacy. In psychopathology isolation can lead to severe character problems of the kind which interfere with“love and work,” and this often on the basis of infantile fixations and lasting immaturities.

Man, in addition to erotic attraction, has developed a selectivity of mutual love that serves the need for a new and shared identity in the procession of generations. Love is the guardian of that elusive and yet all-pervasive power of cultural and personal style which binds into a “way of life” the affiliations of competition and cooperation, procreation and production. The problem is one of transferring the experience of being cared for in a parental setting to an adult affiliation actively chosen and cultivated as a mutual concern within a new generation.

The counterpart of such intimacy, and the danger, is man’s readiness to fortify his territory of intimacy and solidarity by exaggerating small differences and prejudging or excluding foreign influences and people. Insularity thus aggravated can lead to that irrational fear which is easily exploited by demagogic leaders seeking aggrandizement in war and in political conflict.

Love, then, is a mutuality of devotion greater than the antagonisms inherent in divided function.

Maturity (generativity versus stagnation—care)

Evolution has made man the teaching and instituting as well as the learning animal. For dependency and maturity are reciprocal: mature man needs to be needed, and maturity is guided by the nature of that which must be cared for.

Generativity, then, is primarily the concern with establishing and guiding the next generation. In addition to procreativity, it includes productivity and creativity; thus it is psychosocial in nature. From the crisis of generativity emerges the strength of care.

Where such enrichment fails, a sense of stagnation and boredom ensues, the pathological symptoms of which depend on variations in mental epidemiology: certainly where the hypocrisy of the frigid mother was once regarded as a most significant malignant influence, today, when sexual “adjustment” is in order, an obsessive pseudo intimacy and adult self-indulgence are nonetheless damaging to the generational process. The very nature of generativity suggests that the most circumscribed symptoms of its weakness are to be found in the next generation in the form of those aggravated estrangements which we have listed for childhood and youth.

Generativity is itself a driving power in human organization. For the intermeshing stages of child-hood and adulthood are in themselves a system of generation and regeneration given continuity by institutions such as extended households and divided labor.

Thus, in combination, the basic strengths enumerated here and the structure of an organized human community provide a set of proven methods and a fund of traditional reassurance with which each generation meets the needs of the next.

Various traditions transcend divisive personal differences and confusing conditions. But they also contribute to a danger to the species as a whole, namely, the defensive territoriality of the pseudo species, which on seemingly ethical grounds must discredit and destroy threateningly alien systems and may itself be destroyed in the process.

Care is the broadening concern for what has been generated by love, necessity, or accident—a concern which must consistently overcome the ambivalence adhering to irreversible obligation and the narrowness of self-concern.

Old age (integrity versus despair—wisdom)

Strength in the aging and sometimes in the old takes the form of wisdom in its many connotations—ripened “wits,” accumulated knowledge, inclusive understanding, and mature judgment. Wisdom maintains and conveys the integrity of experience, in spite of the decline of bodily and mental functions. Responding to the oncoming generation’s need for an integrated heritage, the wisdom of old age remains aware of the relativity of all knowledge acquired in one lifetime in one historical period. Integrity, therefore, implies an emotional integration faithful to the image bearers of the past and ready to take (and eventually to renounce) leadership in the present.

The lack or loss of this accrued integration is signified by a hidden fear of death: fate is not accepted as the frame of life, death not as its finite boundary. Despair indicates that time is too short for alternate roads to integrity: this is why the old try to “doctor” their memories. Bitterness and disgust mask such despair, which in severe psycho-pathology aggravates senile depression, hypochondria, and paranoiac hate.

A meaningful old age (preceding terminal invalidism) provides that integrated heritage which gives indispensable perspective to those growing up, “adolescing,” and aging. But the end of the cycle also evokes “ultimate concerns,” the paradoxes of which we must leave to philosophical and religious interpreters. Whatever chance man has to transcend the limitations of his self seems to depend on his full (if often tragic) engagement in the one and only life cycle permitted him in the sequence of generations. Great philosophical and religious systems dealing with ultimate individuation seem to have remained (even in their monastic establishments) responsibly related to the cultures and civilizations of their times. Seeking transcendence by renunciation, they remain ethically concerned with the maintenance of the world. By the same token, a civilization can be measured by the meaning which it gives to the full cycle of life, for such meaning (or the lack of it) cannot fail to reach into the beginnings of the next generation and thus enhance the potentiality that others may meet ultimate questions with some clarity and strength.

Wisdom, then, is a detached and yet active con-cern with life in the face of death.


From the cycle of life such dispositions as faith, will power, purposefulness, efficiency, devotion, affection, responsibility, and sagacity (all of which are also criteria of ego strength) flow into the life of institutions. Without them, institutions wilt; but without the spirit of institutions pervading the patterns of care and love, instruction and training, no enduring strength could emerge from the sequence of generations.

We have attempted, in a psychosocial frame, to account for the ontogenesis not of lofty ideals but of an inescapable and intrinsic order of strivings, which, by weakening or strengthening man, dictates the minimum goals of informed and responsible participation.

Psychosocial strength, we conclude, depends on a total process which regulates individual life cycles, the sequence of generations, and the structure of society simultaneously, for all three have evolved together.

Each person must translate this order into his own terms so as to make it amenable to whatever kind of trait inventory, normative scale, measurement, or educational goal is his main concern. Science and technology are, no doubt, changing essential aspects of the course of life, wherefore some increased awareness of the functional wholeness of the cycle may be mandatory. Interdisciplinary work will define in practical and applicable terms what evolved order is common to all men and what true equality of opportunity must mean in planning for future generations.

The study of the human life cycle has immediate applications in a number of fields. Paramount is the science of human development within social institutions. In psychiatry (and in its applications to law), the diagnostic and prognostic assessment of disturbances common to life stages should help to outweigh fatalistic diagnoses. Whatever will prove tangibly lawful about the cycle of life will also be an important focus for anthropology insofar as it assesses universal functions in the variety of institutional forms. Finally, as the study of the life history emerges from that of case histories, it will throw new light on biography and thus on history itself.

Erik H. Erikson



Buhler, Charlotte (1933) 1959 Der menschliche Lebenslauf als psychologisches Problem. 2d ed., rev. Leipzig: Hirzel.

Buhler, Charlotte 1962 Values in Psychotherapy. New York: Free Press.

Erikson, Erik H. (1950) 1964 Childhood and Society.2d ed., rev. & enl. New York: Norton.

Erikson, Erik H. 1958 Young Man Luther. New York:Norton.

Erikson, Erik H. 1964 Insight and Responsibility.New York: Norton.

Erikson, Erik H. 1965 The Ontogeny of Ritualisation in Man. Unpublished manuscript.

Reud, Anna (1936) 1957 The Ego and the Mechanisms of Defense. New York: International Universities Press. → First published as Das Ich und die Abwehrmechanismen.

Freud, Anna 1965 Normality and Pathology in Childhood: Assessment of Development. New York: International Universities Press.

Hartmann, Heinz (1939) 1958 Ego Psychology and the Problem of Adaptation. Translated by David Rapa-port. New York: International Universities Press.→ First published as Ich-Psychologie und Anpassungs-problem.

Mayr, Ernst 1964 The Evolution of Living Systems. National Academy of Sciences, Proceedings 51:934-941.

Werner, Heinz (1926) 1965 Comparative Psychology of Mental Development. Rev. ed. New York: International Universities Press.→ First published as Einfiihrung in die Entwicklungspsychologie.

Eaik H.Erikson

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life cycle

life cycle The complete sequence of events undergone by organisms of a particular species from the fusion of gametes in one generation to the same stage in the following generation. In most animals gametes are formed by meiosis of germ cells in the reproductive organs of the parents. The zygote, formed by the fusion of two gametes, eventually develops into an organism essentially similar to the parents. In plants, however, the products of meiosis are spores, which develop into plants (the gametophyte generation) often very different in form from the spore-forming (sporophyte) generation. The sporophyte generation is restored when gametes, formed by the gametophyte generation, fuse. See alternation of generations.

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life cycle

life cycle The series of developmental changes undergone by the individuals comprising a population, including fertilization, reproduction, and the death of those individuals and their replacement by a new generation. The life ‘cycle’ in fact is linear with respect to individuals, but cyclical with respect to populations. In many animals there is a succession of individuals in the entire cycle with sexual or asexual production linking them. In vertebrates, the life cycle is confined to the period from fusing of the gametes to the death of the resulting individuals.

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MICHAEL ALLABY. "life cycle." A Dictionary of Zoology. 1999. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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life cycle

life cycle A series of developmental changes undergone by the individuals comprising a population, including fertilization, reproduction, and the death of those individuals, and their replacement by a new generation. The life cycle in fact is linear with respect to individuals but cyclical with respect to populations. In many plants there is a succession of individuals in the entire cycle, with sexual or asexual reproduction linking them.

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MICHAEL ALLABY. "life cycle." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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MICHAEL ALLABY. "life cycle." A Dictionary of Plant Sciences. 1998. Retrieved May 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O7-lifecycle.html

life cycle

life cycle A series of developmental changes undergone by the individuals comprising a population, including fertilization, reproduction, and the death of those individuals, and their replacement by a new generation. The life cycle in fact is linear in respect of individuals but cyclical in respect of populations. In many plants there is a succession of individuals in the entire cycle, with sexual or asexual reproduction linking them.

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MICHAEL ALLABY. "life cycle." A Dictionary of Ecology. 2004. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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life cycle

life cy·cle • n. the series of changes in the life of an organism, including reproduction.

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"life cycle." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

"life cycle." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 24, 2016). http://www.encyclopedia.com/doc/1O999-lifecycle.html

"life cycle." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-lifecycle.html

Life Cycle


This entry includes three subentries:

Elders/Old Age

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"Life Cycle." New Dictionary of the History of Ideas. 2005. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

"Life Cycle." New Dictionary of the History of Ideas. 2005. Encyclopedia.com. (May 24, 2016). http://www.encyclopedia.com/doc/1G2-3424300424.html

"Life Cycle." New Dictionary of the History of Ideas. 2005. Retrieved May 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3424300424.html

life cycle

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JOHN DAINTITH. "life cycle." A Dictionary of Computing. 2004. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

JOHN DAINTITH. "life cycle." A Dictionary of Computing. 2004. Encyclopedia.com. (May 24, 2016). http://www.encyclopedia.com/doc/1O11-lifecycle.html

JOHN DAINTITH. "life cycle." A Dictionary of Computing. 2004. Retrieved May 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O11-lifecycle.html

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