Understanding Psychology (10th Ed)

theories of aging 
suggest that human cells have a built-in time limit to their repro-
duction. These theories suggest that after a certain time cells stop dividing or 
become harmful to the body—as if a kind of automatic self-destruct button had 
been pushed. In contrast,  wear-and-tear theories of aging  suggest that the mechan-
ical functions of the body simply work less effi ciently as people age. Waste by-
products of energy production eventually accumulate, and mistakes are made 
when cells divide. Eventually the body in effect wears out like an old automobile 
(Ly et al., 2000; Miquel, 2006; Hayfl ick, 2007).
genetic preprogramming theories of 
aging
Theories that suggest that human 
cells have a built-in time limit to their 
reproduction and that they are no 
longer able to divide after a certain time.
wear-and-tear theories of aging
Theories that suggest that the mechan-
ical functions of the body simply stop 
working effi ciently.
FIGURE 2 
Projections suggest that by 
the year 2050, 20% of the U.S. 
population will be over age 65. What 
implications does this statistic have for 
U.S. society?
Percentage of the U.S. 
population 65 or older 
Percentage of the U.S. 
population younger 
than 65 
P
er
centage 
1910 1930 1950 1970 1990 2010 2030 2050 
Year 
100 
80 
60 
40 
20 
0 
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428 Chapter 
12 
Development
FIGURE 3 
Age-related changes in 
intellectual skills vary according to the 
specifi c cognitive ability in question. 
(Source: Schaie, K. W. (2005). Longitudinal 
studies. In 
Developmental infl uences on adult 
intelligence: The Seattle Longitudinal Study,
Figure 5.7a (p. 127). Copyright © 2005 by 
Oxford University Press, Inc. By permission of 
Oxford University Press, Inc. www.oup.co.uk)
Inductive reasoning
Spacial orientation
Perceptual speed
Numeric ability
Verbal ability
Verbal memory
55
35
88
Mean T
-Scor
es
40
Total Sample
45
50
81
74
67
60
Age 
53
46
39
32
25
Evidence supports both the genetic preprogramming and the wear-and-tear 
views, and it may be that both processes contribute to natural aging. It is clear, how-
ever, that physical aging is not a disease but a natural biological process. Many 
physical functions do not decline with age. For example, sex remains pleasurable 
well into old age (although the frequency of sexual activity decreases), and some 
people report that the pleasure they derive from sex increases during late adulthood 
(Gelfand, 2000; DeLamater & Sill, 2005).
Cognitive Changes: Thinking 
About—and During—
Late Adulthood
At one time, many gerontologists would have agreed with the popular view that 
older adults are forgetful and confused. Today, however, most research indicates that 
this assessment is far from an accurate one of older people’s capabilities. 
One reason for the change in view is that more sophisticated research techniques 
exist for studying the cognitive changes that occur in late adulthood. For example, 
if we were to give a group of older adults an IQ test, we might fi nd that the average 
score was lower than the score achieved by a group of younger people. We might 
conclude that this signifi es a decline in intelligence. Yet, if we looked a little more 
closely at the specifi c test, we might fi nd that the conclusion was unwarranted. For 
instance, many IQ tests include portions based on physical performance (such as 
arranging a group of blocks) or on speed. In such cases, poorer performance on the 
IQ test may be due to gradual decreases in reaction time—a physical decline that 
accompanies late adulthood and has little or nothing to do with older adults’ intel-
lectual capabilities. 
Other diffi culties hamper research into cognitive functioning during late adulthood. 
For example, older people are often less healthy than younger ones; when only healthy
older adults are compared to healthy younger adults, intellectual differences are far less