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AGING

We tend to think of aging in terms of human beings living in time, and, in particular, as the chronology of human experience in later life. But human aging is set in a much wider context, encompassing the biological, geological, and cosmological spheres. Aging is the elegant and continuous means by which the forces of nature, from the microscopic to the universal, create the conditions for regeneration. Many scholars consider aging to be a great equalizer, because it submits all forms of matter, including biological life, to a common set of principles. In human life, there are forms of aging not tied to the individual life course, but to human creations and even whole societies. Buildings become beautiful through weathering; furniture gains a fine patina and great value as it ages; and wines and cheeses are deliberately aged through intricate processes of fermenting, ripening, curing, and storing to enhance their flavor. As for societies across time, they take on the status of "civilizations" if they trace their ancestry and lasting achievements across an extensive span, such as "Old World" European or Asian societies as compared to "New World" countries such as Canada or the United States. The concept of aging, grounded in the realities of both the biological and nonliving material worlds, has thus inspired the human artistic and cultural imagination for millennia.

Rates of aging

Everything that exists in time ages, but rates of aging within living and nonliving realms vary greatly. Geologists and paleontologists who study the earth's history use terms of reference in the hundreds of millions of years. Evidence for the earth's aging is sought in the erosion of mountain ranges or the effects of plate tectonics on the making of continents, and sedimented fossils of extinct plant and animal species mark out a precise record of the earth's aging. These, and related phenomena, beyond the human experience to discern, are subject to the restless vicissitudes of what scientists call the earth's deep time. Physicists, meanwhile, indicate the decay of subatomic particles in units of time so brief as to be unintelligible to the ordinary human mind. Living organisms also vary greatly, but within time spans ranging from minutes to millennia, rather than microseconds to millions or billions of years. From the days or weeks of unicellular organisms to the months of rodents or decades of primates, animal aging appears tied in part to size and complexity. Many plants, however, do not appear to have a "natural" lifespan: There are trees living up to three thousand years, such as the giant California sequoias (the General Sherman Tree in California's Sequoia National Park is estimated to be between three and four thousand years old). Among vertebrates, certain families of species seem to live longer than others: parrots among birds, tortoises among reptiles, and elephants and primates among mammals. What is biologically important is the tempo at which such creatures live their lives rather than the actual length of time they live. In turn, a species' or a creature's tempo is determined by laws of size, environmental niches, reproductive cycles, and metabolic rates. As Stephen Jay Gould notes, a rat may live at a faster rate than an elephant, but this does not mean that it lives any less than an elephant (Gould, 1977).

Among primates, Homo sapiens fully evince the paradox of aging posed by the higher primates. On the one hand, humans live the longest and take the longest time to mature. On the other hand, humans are the most "youthful" primate, because their lengthy neotenic, postnatal development ensures an extended retention of youthful mammalian features (such as a large brain relative to body size and a playful curiosity). Neoteny also means that humans, born relatively helpless and unformed, develop traits and characteristics outside the womb that most primates develop soon after birth, and with which most other mammals are born. Thus nature's experimentation with increased primate intelligence, carried to a high point in humans, has produced a course of life where more areas of behavior are shaped by societal and family learning than by instinct. The special product of this unique evolutionary experiment is human intelligence and the creation of culture and history as key forces in the species' development.

It is a cosmic irony, therefore, that this intelligence allows us to be aware of our own aging. As the only animal conscious of its own mortality, we have invented many different ways to deal with this knowledge across cultures and over the course of history. In Europe, Medieval and Renaissance thinkers saw aging and dying as part of the universal order, represented by the elements of the earth, the cycle of the seasons, and the movement of the planets. The modern biological and social sciences have developed theories of aging based on cellular, neurological, genetic, physiological, psychological, social, and demographic factors. Whereas cytogerontologists, such as Leonard Hayflick, locate the secrets of aging in cellular biology, those in the humanities, such as philosopher Ronald H. Manheimer, seek it in human wisdom and social relationships. Social and psychological gerontologists connect research on individual health, longevity, and cognitive abilities to wider issues of social inequality, gender, race, housing, and lifestyle. Broader still are demographic and global studies that profile the aging characteristics of whole populations. Thus, human aging, from the cell to the population, is a multifarious process that requires study using a multidisciplinary approach.

Measuring human aging

Despite their different backgrounds, researchers who study aging are challenged by the problem of how to measure it. While geological deep time is measured in large-scale epochs and eras, biological aging is calculated in maturational stages within specific life spans. Life spans represent longevity limits that are rarely achieved. The scientific community has set the human life span at 120 years. Life expectancy is the statistical figure based on the average person's length of life. In developed countries, medical advances and improved diet have allowed people to live longer and in greater numbers. Gerontologist Bernice Neugarten has divided the aging population itself into young-old and old-old categories to indicate this development. As the age curve lengthens, however, so do the possible number of diseases and incapacities suffered in later life. At the same time, in developing countries, poverty and the consequences of global inequality continue to undermine healthy populational aging.

Social aging is often measured in terms of ages or stages of life. For example, many African societies use complex and ritualized age-grade systems to identify the passages of life. Medieval European scholars mapped out seven ages of life according to a planetary model, beginning at birth with the moon and ending in old age with Saturn. Shakespeare's character Jaques, in As You Like It, articulated a memorable version of this model, making each age into a theatrical role: the infant, schoolboy, lover, soldier, justice, middle age, and old age—the "last scene of all . . . second childishness and mere oblivion, sans teeth, sans eyes, sans taste, sans everything." (act 2, scene 7) Ages-of-life models became superseded in the nineteenth and twentieth centuries by the sciences of aging, particularly developmental psychology, geriatrics, and gerontology. These sciences increasingly associated aging with the second half of life, or later life, which follows early-life processes of maturation and socialization. In psychology, G. Stanley Hall pioneered aging studies of both early and later life with his two influential books, Adolescence (1904), and Senescence (1922). Erik H. Erikson, a more contemporary developmental psychologist, theorized eight stages of development across the life cycle. He marked each stage by psychosocial modes of growth, crises, and resolutions centered around identity. For instance, in young adulthood (stage 6), the antithesis between generativity and self-absorption creates care. In old age (stage 8), the antithesis between integrity and despair creates wisdom (Erikson 1982). However, the work of Erikson and others in developmental psychology has been criticized by cross-cultural and feminist psychologists for its individualistic, ethnocentric, and masculinist models of the life cycle.

Geriatrics and gerontology emerged as fields of study in the early twentieth century by borrowing the expertise generated in psychology, biology, and medicine. Geriatrics and gerontology introduced two lasting contributions to the measurement of aging. First, aging and old age have their own physical, emotional, and psychological dynamics distinct from other stages of life. Second, aging and old age are best understood if disease pathologies and normal senile conditions are separated. Early clinicians such as Jean-Martin Charcot, Ignatz L. Nascher, Elie Metchnikoff, and Edmund V. Cowdry attributed the problems of aging to specific degenerative processes in the cells, tissues, and organs of the body. Gerontology grew apart from geriatrics in the later twentieth century to include sociological, demographic, and policy studies. Gerontologists also attacked traditionally ageist notions of decline with new, positive measurements of creativity, wisdom, and the benefits of aging. Gerontological research on positive measurements of successful aging has continued with criticism of the negation of aging stemming from modern culture's adulation of youthfulness.

Structuring the life course

Researchers have come to understand more of the complexities of aging throughout the life course; an idea that connects aging to social, gender, family, generational, and environmental contexts. On an individual, or micro, scale, the life course is a lived embodiment of time from which people distill a rich and versatile archive of meaning, memory, narrative, and identity. On a structural, or macro, scale, the life course is an aggregation of knowledges, technologies, institutions, and lifestyles through which aging is socially and temporally organized. Whether people "act their age" or resist it; whether they reckon their time through linear calendars or cyclical anniversaries—they do so through the norms and roles made possible by particular life courses. In Western societies, since the nineteenth century, the modern life course has been structured according to various institutional, industrial, and commercial standards. For example, early life is age graded according to schooling criteria, while later life is age graded according to retirement criteria (usually 65 and over). The modern life course, in turn, evolved in the twentieth century to become an elaborate framework within which people coordinate family, cohort, and intergenerational relations.

Profound shifts in labor, retirement, demographic patterns, and social programs in the late twentieth and early twenty-first centuries have led cultural gerontologists to posit the rise of a postmodern life course (see Featherstone and Hep-worth, 1991). The postmodern life course blurs or loosens the chronological and generational boundaries that have set apart childhood, middle age, and old age throughout the modern era. On the one hand, this has motivated marketing, cosmetic, and leisure industries to target seniors, Third Agers, or boomers (usually those 55 and over), and to recast later life as an active, youthful, consumer experience, one often associated with Hollywood film stars who exemplify the postmodern dream of growing older without aging. On the other hand, the postmodern life course creates new avenues of choice, mobility, well-being, and self-definition in later life, thus empowering senior citizens to innovate resourceful roles and ways of life both for themselves and those who will follow.

Metaphors of aging

Aside from scientific measurements of human aging and the social structuring of the life course, people understand what it means to age and grow older by producing their own metaphoric and symbolic images. The world's religious and literary traditions are a rich source of images about the aging process, while secular examples portray life as a wheel, a journey, a race, a procession, a clock, a hill, over which one climbs, or a return to second childhood. Metaphorical innovations in language can also shake up traditional conventions about aging. Terms such as male menopause or midlife crisis raise the issue of how individual and social aging are intertwined. The term late midlife astonishment (Pearlman, 1993) is a timely metaphorical antidote to centuries of negative images about middle-aged menopausal women. The mommy track is a creative metaphor about women's career path in the workplace, indicating that women must cope with combining careers and parenthood. Whatever their source, metaphors of aging serve to remind us that the human spirit renews itself, in large part, by confronting the paradoxes of living and dying in time.

STEPHEN KATZ

See also AGE; GERIATRICS; GERONTOLOGY; LIFE COURSE; PROLONGEVITY.

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INTERNET RESOURCES

American Association of Retired Persons (AARP) (www.aarp.org).

Administration on Aging (www.aoa.dhhs.gov).

GeroWeb (www.iog.wayne.edu/GeroWeb).

The Gerontological Society of America (www.geron.org).

The National Aging Information Center (www.ageinfo.org).