Aging (life cycle)

Aging, or ageing (British English) is any change in an organism over time. Aging refers to a multidimensional process of physical, psychological, and social change. Some dimensions of aging grow and expand over time, while others decline. Reaction time, for example, may slow with age, while knowledge of world events and wisdom may expand. Research shows that even late in life potential exists for physical, mental, and social growth and development. Aging is an important part of all human societies reflecting the biological changes that occur, but also reflecting cultural and societal conventions. Age is usually measured in full years — and months for young children. A person's birthday is often an important event.

The term "aging" is somewhat ambiguous. Distinctions may be made between "universal aging" (age changes that all people share) and "probabilistic aging" (age changes that may happen to some, but not all people as they grow older, such as the onset of Type Two diabetes). Chronological aging, referring to how old a person is, is arguably the most straightforward definition of aging and may be distinguished from "social aging" (society's expectations of how people should act as they grow older) and "biological aging" (an organism's physical state as it ages). There is also a distinction between "proximal aging" (age-based effects that come about because of factors in the recent past) and "distal aging" (age-based differences that can be traced back to a cause early in person's life, such as childhood poliomyelitis).^[1]

Differences are sometimes made between populations of children;divisions are sometimes made between the young old (65-74), the middle old (75-84) and the oldest old (those aged 85 and above). However, problematic in this is that chronological age does not correlate perfectly with functional age, i.e. two people may be of the same age, but differ in their mental and physical capacities.

Population aging is the increase in the number and proportion of older people in society. Population aging has three possible causes: migration, longer life expectancy (decreased death rate), and decreased birth rate. The societal effects of aging are great. Young people tend to commit most crimes, they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government as opposed to young people, and frequently differing values as well. Older people are also far more likely to vote, and in many countries the young are forbidden from voting. Thus, the aged have comparatively more political influence.

Senescence

Main article: Senescence

In biology, senescence is the state or process of aging. Cellular senescence is a phenomenon where isolated cells demonstrate a limited ability to divide in culture (the Hayflick Limit, discovered by Leonard Hayflick in 1965), while Organismal senescence is the aging of organisms.

After a period of near perfect renewal (in humans, between 20 and 50 years of age^{[citation needed]}), organismal senescence is characterized by the declining ability to respond to stress, increasing homeostatic imbalance and increased risk of disease. This irreversible series of changes inevitably ends in death.

Some researchers (specifically biogerontologists) are treating aging as a disease. As genes that have an effect on aging are discovered, aging is increasingly being regarded in a similar fashion to other genetic conditions, potentially "treatable."

Indeed, aging is not an unavoidable property of life. Instead, it is the result of a genetic program. Numerous species show no sign of aging ("negligible senescence'), the best known being trees like the bristlecone pine, fish like the sturgeon, invertebrates like the quahog or sea anemone ^[2].

Aging is believed to be favored by natural selection because it accelerates the evolution rate of a species by increasing the number of generations per unit of time. By dying away, the old individuals liberate the resources for their offspring, thus increasing their chance of survival. Essentially, aging is the result of investing resources in reproduction rather than maintenance of the body, the "Disposable Soma" theory of Kirkwood & Holiday ^[3].

In humans and other animals, cellular senescence has been attributed to the shortening of telomeres with each cell cycle; when telomeres become too short, the cells die. The length of telomeres is therefore the "molecular clock," predicted by Hayflick. Telomere length is maintained in immortal cells (e.g. germ cells) by the enzyme telomerase. In the laboratory, mortal cell lines can be immortalized by the activation of their telomerase gene, present in all cells but active in few cell types. Cancerous cells must become immortal to multiply without limit. This important step towards carcinogenesis implies, in 85% of cancers, the reactivation of their telomerase gene by mutation. Since this mutation is rare, the telomere "clock" can be seen as a protective mechanism against cancer ^[4].

Other genes are known to affect the aging process, the sirtuin family of genes have been shown to have a significant effect on the lifespan of yeast and nematodes. Over-expression of the RAS2 gene increases lifespan in yeast substantially.

In addition to genetic ties to lifespan, diet has been shown to substantially affect lifespan in many animals. Specifically, caloric restriction (that is, restricting calories to 30-50% less than an ad libitum animal would consume, while still maintaining proper nutrient intake), has been shown to increase lifespan in mice up to 50%. Caloric restriction works on many other species beyond mice (including species as diverse as yeast and Drosophila), and appears (though the data is not conclusive) to increase lifespan in primates according to a study done on Rhesus monkeys at the National Institute of Health (US). Since, at the molecular level, age is counted not as time but as the number of cell doublings, this effect of calorie reduction could be mediated by the slowing of cellular growth and, therefore, the lengthening of the time between cell divisions.

Drug companies are currently searching for ways to mimic the lifespan-extending effects of caloric restriction without having to severely reduce food consumption.

Dividing the lifespan

A human life is often divided into various ages. Historically, the lifespan of man was divided into seven ages; because biological changes are slow moving and vary from person to person, arbitrary dates are usually set to mark periods of human life. In some cultures the divisions given below are quite varied.

In the USA, adulthood legally begins at the age of eighteen or nineteen, while old age is considered to begin at the age of legal retirement (approximately 65).

• Pre-conception: ovum, spermatozoon, possible pre-existence
• Conception: fertilization
• Pre-birth: conception to birth
• Infancy: Birth to 2
• Childhood: 2 to 12
• Adolescence: 13 to 19
• Early adulthood: 20 to 34
• Middle adulthood: 35 to 54
• Late adulthood: 55+
• Death
• Post-Death: Decomposition and possible afterlife

Ages can also be divided by decade:

• Denarian: someone between 10 and 19 years of age
• Vicenarian: someone between 20 and 29 years of age
• Tricenarian: someone between 30 and 39 years of age
• Quadragenarian: someone between 40 and 49 years of age
• Quinquagenarian: someone between 50 and 59 years of age
• Sexagenarian: someone between 60 and 69 years of age
• Septuagenarian: someone between 70 and 79 years of age
• Octogenarian: someone between 80 and 89 years of age
• Nonagenarian: someone between 90 and 99 years of age
• Centenarian: someone between 100 and 109 years of age
• Supercentenarian: someone over 110 years of age

Cultural variations

In some cultures (for example Serbian and Russian) there are two ways to express age: by counting years with or without including current year. For example, it could be said about the same person that he is twenty years old or that he is in twenty-first year of his life.

Considerable numbers of cultures have less of a problem with age compared with what has been described above, and it is seen as an important status to reach stages in life, rather than defined numerical ages. Advanced age is given more respect and status.

East Asian age reckoning is different from that found in Western culture. Traditional Chinese culture uses a different aging method, called Xusui (虛歲) with respect to common aging which is called Zhousui (周歲). In the Xusui method, people are born at age 1, not age 0.

Society

Legal

There are variations in many countries as to what age a person legally becomes an adult.

Most legal systems define a specific age for when an individual is allowed or obliged to do something. These ages include voting age, drinking age, age of consent, age of majority, age of criminal responsibility, marriageable age, age where one can hold public office, and mandatory retirement age. Admission to a movie for instance, may depend on age according to a motion picture rating system. A bus fare might be discounted for the young or old.

Similarly in many countries in jurisprudence, the defense of infancy is a form of defense by which a defendant argues that, at the time a law was broken, they were not liable for their actions, and thus should not be held liable for a crime. Many courts recognize that defendants who are considered to be juveniles may avoid criminal prosecution on account of their age.

Economics and marketing

The economics of aging are also of great import. Children and teenagers have little money of their own, but most of it is available for buying consumer goods. They also have considerable impact on how their parents spend money.

Young adults are an even more valuable cohort. They often have jobs with few responsibilities such as a mortgage or children. They do not yet have set buying habits and are more open to new products.

The young are thus the central target of marketers.^[5] Television is programmed to attract the range of 15 to 35 year olds. Movies are also built around appealing to the young.

Health care demand

Many societies in the rich world, i.e. Western Europe and Japan, have aging populations. While the effects on society are complex, there is a concern about the impact on health care demand. The large number of suggestions in the literature for specific interventions to cope with the expected increase in demand for long-term care in aging societies can be organized under four headings: improve system performance; redesign service delivery; support informal caregivers; and shift demographic parameters.^[6]

Cognitive effects

Steady decline in many cognitive processes are seen across the lifespan, starting in one's thirties. Research has focused in particular on memory and aging, and has found decline in many types of memory with aging, but not in semantic memory or general knowledge such as vocabulary definitions, which typically increases or remains steady. Early studies on changes in cognition with age generally found declines in intelligence in the elderly, but studies were cross-sectional rather than longitudinal and thus results may be an artefact of cohort rather than a true example of decline. Intelligence may decline with age, though the rate may vary depending on the type, and may in fact remain steady throughout most of the lifespan, dropping suddenly only as people near the end of their lives. Individual variations in rate of cognitive decline may therefore be explained in terms of people have different lengths of life.^[1]

Coping and well-being

Psychologists have examined coping skills in the elderly. Various factors, such as social support, religion and spirituality, active engagement with life and having an internal locus of control have been proposed as being beneficial in helping people to cope with stressful life events in later life.^[7][8][9] Social support and personal control are possibly the two most important factors that predict well-being, morbidity and mortality in adults.^[10] Other factors that may link to well-being and quality of life in the elderly include social relationships (possibly relationships with pets as well as humans), and health.^[11]

Individuals in different wings in the same retirement home have demonstrated a lower risk of mortality and higher alertness and self-rated health in the wing where residents had greater control over their environment,^[12][13] though personal control may have less impact on specific measures of health.^[9] Social control, perceptions of how much influence one has over one's social relationships, shows support as a moderator variable for the relationship between social support and perceived health in the elderly, and may postiviely influence coping in the elderly.^[14]

Religion

Religion has been an important factor used by the elderly in coping with the demands of later life, and appears more often than other forms of coping later in life.^[15] Religious commitment may also be associated with reduced mortality,^{[citation needed]} though religiosity is a multidimensional variable; while participation in religious activities in the sense of participation in formal and organized rituals may decline, it may become a more informal, but still important aspect of life such as through personal or private prayer.^[16]

Self-rated health

Self-ratings of health, the beliefs in one's own health as excellent, fair or poor, has been correlated with well-being and mortality in the elderly; positive ratings are linked to high well-being and reduced mortality.^[17][18] Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better than that of their ill counterparts, though this link has been observed even in studies which have controlled for socioeconomic status, psychological functioning and health status.^[19] This finding is generally stronger for men than women,^[18] though the pattern between genders is not universal across all studies, and some results suggest sex-based differences only appear in certain age groups, for certain causes of mortality and within a specific sub-set of self-ratings of health.^[19]

Retirement

Retirement, a common transition faced by the elderly, may have both positive and negative consequences.^[20]

Societal impact

Societal aging refers to the demographic aging of populations and societies.^[21] Cultural differences in attitudes to aging have been studied.^{[citation needed]}

Emotional improvement

Given the physical and cognitive declines seen in aging, a surprising finding is that emotional experience improves with age. Older adults are better at regulating their emotions and experience negative affect less frequently than younger adults and show a positivity effect in their attention and memory. The emotional improvements show up in longitudinal studies as well as in cross-sectional studies, and so cannot be entirely due to only the happier individuals surviving.

Terminology

The concept of successful aging can be traced back to the 1950s, and popularised in the 1980s. Previous research into aging exaggerated the extent to which health disabilities, such as diabetes or osteoporosis, could be attributed exclusively to age, and research in gerontology exaggerated the homogeneity of samples of elderly people.^[22][23]

Successful aging consists of three components:^[24]

1. Low probability of disease or disability;
2. High cognitive and physical function capacity;
3. Active engagement with life.

A greater number of people self-report successful aging than those that strictly meet these criteria.^[22]

Successful aging may be viewed an interdisciplinary concept, spanning both psychology and sociology, where it is seen as the transaction between society and individuals across the life span with specific focus on the later years of life.^[25] The terms "healthy aging"^[22] "optimal aging" have been proposed as alternatives to successful aging.

Six suggested dimensions of successful aging include:^[9]

1. No physical disability over the age of 75 as rated by a physician;
2. Good subjective health assessment (i.e. good self-ratings of one's health);
3. Length of undisabled life;
4. Good mental health;
5. Objective social support;
6. Self-rated life satisfaction in eight domains, namely marriage, income-related work, children, friendship and social contacts, hobbies, community service activities, religion and recreation/sports

Theories

Non-biological theories

Modernization Theory

This is the view that the status of the elderly has declined since industrialization and the spread of technology.

Cognitive Theory

A view of aging that emphasizes individual subjective perception, rather than actual objective change itself, as the factor that determines behavior associated with advanced age.

Demographic Transition Theory

The idea that population aging can be explained by a decline in both birthrates and death rates following industrialization.

Disuse Theory

The idea states that cognitive and physical skills will atrophy unless one continuously practices them.

Exchange Theory

The idea that interaction in social groups is based on the reciprocal balancing of rewards depending on actions performed

Political Economy Theory

A societal perspective on the aging process that explains that the status and resources of the elderly, as well as how people age, are shaped by each person's place in the social structure and the economic and political forces that impact their sociopolitical location.

Disengagement Theory

This is the idea that separation of older people from active roles in society is normal and appropriate, and benefits both society and older individuals. Disengagement theory, first proposed by Cumming and Henry, has received considerable attention in gerontology, but has been much criticised.^[1] The original data on which Cumming and Henry based the theory were from a rather small sample of older adults in Kansas City, and from this select sample Cumming and Henry then took disengagement to be a universal theory.^[26] There are research data suggesting that the elderly who do become detached from society as those were initially reclusive individuals, and such disengagement is not purely a response to aging.^[1]

Activity Theory

In contrast to disengagement theory, this theory implies that the more active elderly people are, the more likely they are to be satisfied with life. The view that elderly adults should maintain well-being by keeping active has had a considerable history, and since 1972, this has become to be known as activity theory.^[26] However, this theory may be just as inappropriate as disengagement for some people as the current paradigm on the psychology of aging is that both disengagement theory and activity theory may be optimal for certain people in old age, depending on both circumstances and personality traits of the individual concerned.^[1] There are also data which query whether, as activity theory implies, greater social activity is linked with well-being in adulthood.^[26]

• Selectivity Theory - mediates between Activity and Disengagement Theory, which suggests that it may benefit older people to become more active in some aspects of their lives, more disengaged in others.^[26]

  Continuity Theory

  The view that in aging people are inclined to maintain, as much as they can, the same habits, personalities, and styles of life that they have developed in earlier years. Continuity theory is Atchley's theory that individuals, in later life, make adaptations to enable them to gain a sense of continuity between the past and the present, and the theory implies that this sense of continuity helps to contribute to well-being in later life.^[11] Disengagement theory, activity theory and continuity theory are social theories about ageing, though all may be products of their era rather than a valid, universal theory.

  Biological theories

  Telomere Theory

  Telomeres (structures at the ends of chromosomes) have experimentally been shown to shorten with each successive cell division. Shortened telomeres activate a mechanism that prevents further cell multiplication. This may be an important mechanism of aging in tissues like bone marrow and the arterial lining where active cell division is necessary.

  Reproductive-Cell Cycle Theory

  The idea that aging is regulated by reproductive hormones that act in an antagonistic pleiotrophic manner via cell cycle signaling, promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence (dyosis).

  Wear-and-Tear theory

  The idea that changes associated with aging are the result of chance damage that accumulates over time.

  Somatic Mutation Theory

  The biological theory that aging results from damage to the genetic integrity of the body’s cells.

  Error Accumulation Theory

  The idea that aging results from chance events that gradually damage the genetic code.

  Accumulative-Waste Theory

  The biological theory of aging that points to a buildup of cells of waste products that presumably interferes with metabolism.

  Autoimmune Theory

  The idea that aging results from an increase in autoantibodies that attack the body's tissues. A number of diseases associated with aging, such as atrophic gastritis and Hashimoto's thyroiditis, are probably autoimmune in this way.

  Aging-Clock Theory

  The theory that aging results from a preprogrammed sequence, as in a clock, built into the operation of the nervous or endocrine system of the body. In rapidly dividing cells the shortening of the telomeres would provide just such a clock.

  Cross-Linkage Theory

  The idea that aging results from accumulation of cross-linked compounds that interfere with normal cell function.

  Free-Radical Theory

  The idea that free radicals (unstable and highly reactive organic molecules, also named reactive oxygen species or oxidative stress) create damage that gives rise to symptoms we recognize as aging.

  Mitohormesis

  It has been known since the 1930s that restricting calories while maintaining adequate amounts of other nutrients prevents aging across a broad range of organism. Recently, Michael Ristow has shown that this delay of aging is due to increased formation of free radicals within the mitochondria causing a secondary induction of increased antioxidant defence capacity.^[27]

  Measure of age

  The normal point of time from where to measure the age of a human being is from birth. Age in prenatal development is normally measured in gestational age, taking the last menstruation of the woman as a point of beginning. Alternatively, fertilization age, beginning from fertilization can be taken.

  Age is often rounded downward to an integer, where the time of birth is taken to have been 0:00 (in other words, the number of days is first rounded upward, before rounding downward to whole years). Thus the age range 4-11 is until the 12th birthday.

  See also

  

  Look up aging in Wiktionary, the free dictionary.

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  Wikiquote has a collection of quotations related to:

  Aging (life cycle)

  • Adultism
  • Aging brain
  • Aging Research Centre
  • Biodemography
  • Biological immortality
  • Calorie restriction
  • Life expectancy
  • List of life extension-related topics
  • Longevity
  • Maturity (psychological)
  • Memory and aging
  • Michael Ristow
  • Mitohormesis
  • Orthomolecular medicine
  • Population aging
  • Retirement
  • Senescence
  • The Grim Reaper Gene
  • Youth bulge

  Notes

  1. ^ ^{a b c d e}
  2. ^ Physiological Basis of Aging and Geriatrics, By Paola S. Timiras, p.26, Published 2003 Informa Health Care, ISBN 0849309484
  3. ^ Genetic Effects on Aging II, By David E. Harrison, p.9, Published 1990 CRC Press, ISBN 0936923318
  4. ^ name="pmid10647931">Hanahan D, Weinberg RA (2000). "The hallmarks of cancer". Cell 100 (1): 57–70. PMID 10647931. 
  5. ^ Krulwich, Robert (2006). Does Age Quash Our Spirit of Adventure?. All Things Considered. NPR. Retrieved on 2006-08-22.
  6. ^ Saltman, R.B.; Dubois, H.F.W.; Chawla, M. (2006). "The Impact Of Aging On Long-term Care In Europe And Some Potential Policy Responses". International Journal of Health Services 36 (4): 719-746. Retrieved on 2008-02-11. 
  7. ^ Schulz R, Heckhausen J (1996). "A life span model of successful aging". Am Psychol 51 (7): 702–14. PMID 8694390. 
  8. ^ Windsor TD, Anstey KJ, Butterworth P, Luszcz MA, Andrews GR (2007). "The role of perceived control in explaining depressive symptoms associated with driving cessation in a longitudinal study". Gerontologist 47 (2): 215–23. PMID 17440126. 
  9. ^ ^{a b c} Diane F. Gilmer; Aldwin, Carolyn M. (2003). Health, illness, and optimal aging: biological and psychosocial perspectives. Thousand Oaks: Sage Publications. ISBN 0-7619-2259-8. 
  10. ^ Smith GC, Kohn SJ, Savage-Stevens SE, Finch JJ, Ingate R, Lim YO (2000). "The effects of interpersonal and personal agency on perceived control and psychological well-being in adulthood". Gerontologist 40 (4): 458–68. PMID 10961035. 
  11. ^ ^{a b} Bowling, Ann (2005). Ageing well: quality of life in old age. [Milton Keynes]: Open University Press. ISBN 0335215092. 
  12. ^ Langer EJ, Rodin J (1976). "The effects of choice and enhanced personal responsibility for the aged: a field experiment in an institutional setting". J Pers Soc Psychol 34 (2): 191–8. PMID 1011073. 
  13. ^ Rodin J, Langer EJ (1977). "Long-term effects of a control-relevant intervention with the institutionalized aged". J Pers Soc Psychol 35 (12): 897–902. PMID 592095. 
  14. ^ Bisconti, T.L. (1999). "Perceived social control as a mediator of the relationships among social support, psychological well-being, and perceived health". The Gerontologist 39 (1): 94-103. Retrieved on 2008-02-11. 
  15. ^ McFadden, S (2005), Gerontology and the Psychology of Religion; inPark, Crystal L.; Raymond F. Paloutzian. Handbook of the Psychology of Religion and Spirituality. New York: The Guilford Press. ISBN 1-57230-922-9. 
  16. ^ Mindel CH, Vaughan CE (1978). "A multidimensional approach to religiosity and disengagement". J Gerontol 33 (1): 103–8. PMID 618958. 
  17. ^ Idler, E.L. (2003). "Discussion: Gender Differences in Self-Rated Health, in Mortality, and in the Relationship Between the Two". The Gerontologist 43 (3): 372-375. Retrieved on 2008-02-11. 
  18. ^ ^{a b} Deeg, D.J.H.; Bath, P.A. (2003). "Self-Rated Health, Gender, and Mortality in Older Persons: Introduction to a Special Section". The Gerontologist 43 (3): 369-371. Retrieved on 2008-02-11. 
  19. ^ ^{a b} Benyamini, Y.; Blumstein, T.; Lusky, A.; Modan, B. (2003). "Gender Differences in the Self-Rated Health-Mortality Association: Is It Poor Self-Rated Health That Predicts Mortality or Excellent Self-Rated Health That Predicts Survival?". The Gerontologist 43 (3): 396-405. Retrieved on 2008-02-11. 
  20. ^ Panek, Paul E.; Hayslip, Bert (1989). Adult development and aging. San Francisco: Harper & Row. ISBN 0060450126. 
  21. ^ Sarah Harper, 2006, Aging Societies: Myths, Challenges and Opportunities.
  22. ^ ^{a b c} Strawbridge WJ, Wallhagen MI, Cohen RD (2002). "Successful aging and well-being: self-rated compared with Rowe and Kahn". Gerontologist 42 (6): 727–33. PMID 12451153. 
  23. ^ Rowe JW, Kahn RL (1987). "Human aging: usual and successful". Science 237 (4811): 143–9. PMID 3299702. 
  24. ^ Rowe JW, Kahn RL (1997). "Successful aging". Gerontologist 37 (4): 433–40. PMID 9279031. 
  25. ^ Fentleman, DL (1990), Successful aging in a postretirement society; in Baltes, Margret M.; Baltes, Paul B. (1990). Successful aging: perspectives from the behavioral sciences. Cambridge, UK: Cambridge University Press. ISBN 052143582X. 
  26. ^ ^{a b c d}
  27. ^ Schulz TJ, Zarse K, Voigt A, Urban N, Birringer M, Ristow M (2007). "Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress". Cell Metab. 6 (4): 280–93. doi:10.1016/j.cmet.2007.08.011. PMID 17908557. 

  
  

  References

  • Bass, S.A. (2006). Gerontological Theory: The Search for the Holy Grail. The Gerontologist, 46, 139-144.
  • Bath, P.A. (2003). Differences between older men and woman in the Self-Rated Health/ Mortality Relationship. The Gerontologist, 43 387-94
  • Charles, S.T., Reynolds, C.A., & Gatz, M. (2001). Age-related differences and change in positive and negative affect over 23 years. Journal of Personality and Social Psychology, 80, 136-151.
  • Fentleman, D.L., Smith, J. & Peterson, J. (1990). Successful aging in a postretirement society. In P.B. Baltes and M.M. Baltes (Eds.).Successful aging: Perspectives from the Behavioural Sciences. pp50-93
  • Mather, M., & Carstensen, L. L. (2005). Aging and motivated cognition: The positivity effect in attention and memory. Trends in Cognitive Sciences 9, 496-502. PDF
  • Masoro E.J. & Austad S.N.. (eds.): Handbook of the Biology of Aging, Sixth Edition. Academic Press. San Diego, CA, USA, 2006. ISBN 0-12-088387-2
  • Moody, Harry R. Aging: Concepts and Controversies. 5th ed. California: Pine Forge Press, 2006.
  • Rowe, J.D. & Kahn, R.L. (1987). Human aging: Usual and successful. Science, 237, 143-149
  • Rowe, J.D. & Kahn, R.L.(1997). Successful aging. The Gerontologist, 37 (4) 433-40
  • Strawbridge, W.J., Wallhagen, M.I. & Cohen, R.D. (2002). Successful aging and well-being: Self-rated compared with Rowe and Kahn. The Gerontologist, 42, (6)
  • Zacks, R.T., Hasher, L., & Li, K.Z.H. (2000). Human memory. In F.I.M. Craik & T.A. Salthouse (Eds.), The Handbook of Aging and Cognition (pp. 293-357). Mahwah, NJ: Erlbaum.

  External links

  • The arrow of time - a photo-essay of a family aging, with yearly portraits over 30 years
  • National Institute on Aging (U.S.)
  • Books on Aging published in 2007

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  Other	Metamorphosis - Regeneration - Aging - Model organisms - Compartment

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  Stages	Prenatal development • Pre- and perinatal psychology • Infancy • Toddlerhood • Childhood • Preadolescence • Puberty • Adolescence • Adulthood - Early adulthood • Middle adulthood • Late adulthood
  Development	Child development (stages) • Youth development • Ageing & Senescence
  Theorists-theories	John Bowlby-attachment • Erik Erikson-psychosocial • Sigmund Freud-psychosexual • Lawrence Kohlberg-moral • Jean Piaget-cognitive • Lev Vygotsky-cultural-historical

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