COHORT PERSPECTIVES(1968); yet persistent failure to comprehend this
duality has perpetuated numerous false stereo-
types (e.g., that intelligence or physical function-
ing begin inevitable declines at very early ages).
Properly interpreted, of course, a cross-sec-
tional perspective has its special uses: for describ-
ing current differences and similarities, social rela-
tionships, and interactions among coexisting people
who differ in age-cum-cohort membership. Thus,
for example, issues of ‘‘intergenerational equity’’
require explication by both age and cohort, as a
larger share of the federal budget is reportedly
spent on cohorts of people now old than on co-
horts of children (Duncan, Hill, and Rodgers 1986;
Preston 1984).
Across Time. Comprehension of the underly-
ing dynamics of the age strata requires going
beyond the single cross-sectional snapshot to a
sequence of cross-sections (the moving perpen-
dicular line in Figure 1), as successive cohorts
interact with historical trends in the society (Ryder
1965; Riley 1982). Historical change means not
only that new cohorts are continually entering the
system through birth or immigration, while others
are leaving it through death or emigration (e.g.,
men tend to die earlier than women, and blacks
earlier than whites). Historical change also means
that the members of all existing cohorts are simul-
taneously aging and thus moving from younger to
older strata. As successive cohorts move concur-
rently through the system, they affect the age
strata in several ways. They can alter the numbers
and kinds of people in particular strata, as each
cohort starts the life course with a characteristic
size, genetic makeup, sex ratio, racial and ethnic
background, and other properties that are subse-
quently modified through migration, mortality,
and environmental contact. The succession of co-
horts can also affect the capacities, attitudes, and
actions of people in particular strata as the mem-
bers of each cohort bring to society their experi-
ences with the social and environmental events
spanned by their respective lifetimes.
The most significant alterations in the age
composition of modern societies stem from the
dramatic and unprecedented increases in the lon-
gevity of successive cohorts. Age pyramids dia-
gramming the age composition of the United States
in 2010 compared with 1955, for example, demon-
strate that entirely new strata have been added at
the oldest ages (Taeuber 1992)—strata of old peo-
ple who are healthier and more competent than
their predecessors (Manton, Corder, and Stallard
1997). The advent of these ‘‘new’’ old people is
already having untold consequences: Individuals
now have time to spread education, work, family
activities, and leisure more evenly over their long
lives, and wider structural opportunities are need-
ed in society for the age-heterogenous population.SOCIAL STRUCTURAL PERSPECTIVESCohorts, as described above, are composed of
people, who age and fit together in strata to form
the composition of the population; but cohorts
also shape, and are shaped by social structures—
the surrounding families, communities, work or-
ganizations, educational institutions, and the like.
Against the backdrop of history, social structures,
like lives, tend to change, and two ‘‘dynamisms’’—
changing structures and changing lives—are in
continuing interplay, as each influences the other.
Thus full understanding of cohorts requires un-
derstanding their reciprocal relations with struc-
tures (as in Foner and Kertzer 1978; Mayer 1988).
Toward this end, some studies examine how the
processes of aging and cohort flow relate to struc-
tures, while other studies examine the congru-
ence—or lack of congruence—between age com-
position and social structures.
Aging and Structures. Because cohorts differ
in size and character, and because their members
age in new ways (the diagonal lines in Figure 1),
they exert collective pressures for adjustments—
not only in people’s ideas, values, and beliefs—but
also in role opportunities throughout the social
institutions.
As one example, the influences of cohort dif-
ferences in size were defined early by Joan Waring’s
(1975) powerful analysis of ‘‘disordered cohort
flow.’’ This disordered flow has been dramatically
brought to attention as the Baby Boom cohorts
first pressed for expansions in the school systems
and the labor force, and will become the twenty-
first century ‘‘senior boom’’ that will exacerbate
the inadequacy of roles for the elderly. Later, as
large cohorts were followed by smaller successors,
ways were sought to reduce these expanded struc-
tures again. Meanwhile, as structures changed, the
lives of people moving through these structures
also changed.