Adulthood and Aging Research Paper

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Until the beginning of the 20th century, the majority of a person’s life took place during childhood and adolescence. Therefore, it is no surprise that the vast majority of thinking, philosophizing, and researching on human development centered on these two areas. With advancements in nutrition, medicine, and exercise physiology, life expectancy grew during the 20th century faster than at any other time in human history. In fact, the average human’s life expectancy rose from 47 years in 1900 to 77 years in 2002.

Why the history lesson? Simple; the history of human life on this planet is important in understanding the study of human development. Even with the increase in life expectancy that has limited the amount of time spent in childhood and adolescence from half of one’s life down to less than a quarter, the bulk of research in development still focuses on those areas. Most colleges and universities in this country offer a child psychology, adolescent psychology, or child and adolescent psychology class. However, smaller numbers offer classes in adulthood and aging. There are more texts on childhood and adolescence, covering the first 13 to 18 years of life, than there are covering the last 60 years of life.

So, why has this area in human development been neglected for so long? Basically, many researchers and philosophers believed that development was set by adolescence. In addition, researchers thought that any development that occurred after childhood and adolescence was minimal, at best (Cartwright, 2001). Not until the latter part of the 20th century did the topic area of adulthood and aging gather enough momentum to challenge the aforementioned notions.

A Change In Focus

Researchers are beginning to turn their attention to the importance of life after adolescence, and today most researchers in the realm of human development believe that development does not cease once adolescence is over. Two things have lead to this shift in paradigm in developmental research: (a) the “baby boomer” generation and (b) the developmental issue of stability versus change.

One of the real forces that prompted researchers to begin investigating development past adolescence was the aging population of the “baby boomer” generation (Rosenfeld & Stark, 1987). In 1940 there were a little over 9 million Americans who were over the age of 65. By 2000, this number had risen to a little over 35 million, with just short of 70 million people expected by 2040 (U.S. Census Bureau, n.d.). With the growth in this generation of adults, researchers are beginning to realize the importance of aging. In other words, researchers are now acknowledging that development continues throughout the life span and does not stop at adolescence.

The second major force behind the momentum change in development is a function of the three major developmental issues: (a) nature versus nurture, (b) continuity

versus discontinuity, and (c) stability versus change. The issue of nature versus nurture has been around as long as people have discussed human development. Basically, the question is, are people who they are because of nature (i.e., genetics) or because of nurture (i.e., environmental influence)? For the most part, people have agreed that it is more than likely a combination of the two. Specifically, nature sets a reaction range for people to behave in a predisposed way along a finite continuum. Nurture then will determine where one falls along this continuum due to the impact of the environmental influence in his or her life. This developmental issue is not as important to adulthood and aging as it is in earlier periods of development.

The second developmental issue is whether development is continuous (i.e., gradual and cumulative) or discontinuous (i.e., stagelike, with critical periods of development). Those who argue for the continuous approach state that development occurs in succession with each experience or life event building on the previous event to create a whole person. Therefore, a child learning to crawl does not just happen upon this circumstance. Rather, it is a culmination of learning to put weight on his or her forearms, roll over, sit up on all fours, and move in a meaningful direction. On the other hand, a person subscribing to the discontinuist model of development would argue that language has a critical period or a set time frame within which to be developed. Specifically, as humans, people must acquire language well before puberty or they will never have native-like abilities (Pinker, 1994). This fact argues that there is some type of critical period in which language acquisition must take place and cannot be overcome by a gradual cumulative process.

The final highly debated developmental issue has to do with stability versus change. Particularly, are people always basically the same individual, growing into simply older renditions of their earlier selves (i.e., stability), or do people become different individuals from the people they once were as they grow and mature and develop (i.e., change; Schaie, 1973)? It is this question of stability or change that has helped shift the focus of many people in development away from only evaluating childhood and adolescence to examining the importance of adulthood and aging. After all, the issue of stability or change cannot be answered based on only a quarter of an individual’s life; rather, one has to take into account the entire life span.

Theoretical Approaches

Historically, certain theorists have dominated the field of psychology (rightfully so or not). The domain of developmental psychology is no exception. Typically, developmental psychologists reference Piaget, Freud, Vygotzky, Erickson, and others as important theorists in their field. With the exception of Erickson, most focus only on childhood and adolescence.

Piaget’s (1950) theory on cognitive development has four stages that people progress through as their mental processes develop. However, by the time people reach puberty, Piaget believed that they had progressed as far as they could in their complexity of thinking. Likewise, Freud’s Psychosexual Theory of development stresses 5 stages in which one’s adult personality is a result of conflict resolution during the first 12 years of life. Again like Piaget, Freud believed that development was determined by puberty. Finally, Vygotsky’s (1935/1978) theory on the Zone of Proximal Development (ZPD) focuses on people’s change in knowledge, whether it is situated (i.e., distributed among people in their environment) or collaborative (i.e., achieved through collaboration). Still, this theory is grounded in work with children and adolescence in educational settings and has yet to be applied to adult development.

However, not all theorists focus only on the early years of development. Erick Erickson’s (1950, 1968) theory of psychosocial development, in which he argues that development is primarily a result of social interactions, has three stages that occur during adult development (intimacy vs. isolation, generativity vs. stagnation, and integrity vs. despair). However, Erickson’s previous five stages all take place during the early years of development, and the vast majority of work focuses on these stages. One theorist who is similar to Erickson but has focused his work on adulthood is Levinson (1978), who developed the seasons of a man’s life. Levinson’s theory describes a number of stages and transitions in the life span ranging from 18 to 75 years of age. This theory, like Erickson’s, involves resolving a crisis in order to develop into a complete person. The difference is that Erickson’s focus was over the whole life span, whereas Levinson’s is more concerned with the concept of the midlife crisis. Additionally, work has been done to extend Piaget’s theories on cognitive development. Schaie and Willis (2000), Perry (1970), and others who propose a fifth stage to Piaget have all influenced the idea that cognitive development continues well into adulthood.

Simply, the theorists and major theoretical approaches to adulthood and aging are not as well known as those for childhood and adolescence, yet their impact on understanding adulthood and aging has been just as valuable. Throughout the rest of the chapter, the importance of each of these theorists will be further explored, as well as the importance of other, lesser known theorists and theoretical approaches.


How do people know about the developmental track that is adulthood and aging? The answer: research. Traditional research methods (i.e., experimental and descriptive approaches) are always used when exploring adulthood and aging. Yet, a few types of research are more fitting when exploring adulthood and aging issues. Specifically, those research methods that are used to assess the developmental issue of stability versus change are most beneficial. These include longitudinal, cross-sectional, and sequential designs.

Longitudinal approaches are strategies that look to assess the same individuals over a period of time. For example, if researchers wanted to determine if intelligence is stable or if it changes over the life span, they could do a longitudinal study in which a group of people was given an intelligence test at 20, again at 40, and again at 60. This would show how intelligence changes for the same group of people over a 40-year time period. Even though this approach is beneficial in studying change, it is obviously time consuming, expensive, often highly attritional (people drop out of the study), and those participants who do stay with the study for a long period are usually somewhat unique, leading to results that cannot always be generalized.

Cross-sectional approaches are used many times in place of longitudinal studies due to the disadvantages listed above. A cross-sectional study is one in which a researcher studies a number of people at different points in life at the same time. Therefore, if someone again wanted to determine if intelligence is stable or if it changes over the life span, groups of 20-, 40-, and 60-year-olds could be given an intelligence test at the same time (same day, location, etc.). However, like longitudinal approaches, this research approach has its drawbacks. For example, a cross-sectional approach cannot truly determine if individuals are stable in their behaviors because the researcher does not look at the same individual but rather a group at one point in time.

Finally, to combat some of the drawbacks of the aforementioned designs, a researcher could use a combination of longitudinal and cross-sectional approaches—a sequential design. A researcher using this design type and again testing intelligence might start off with people who are 20, 40, and 60 years of age, testing them at the same time (cross-sectional) and then in 1 year, 2 years, or more test the same groups again (longitudinal). This approach has all the advantages and disadvantages of cross-sectional and longitudinal approaches, but it will provide information that neither of these can gather alone.

It is only with these research approaches, as along with the traditional use of experimental and descriptive research methods, that researchers can obtain answers concerning adult development. These approaches have yielded valuable information concerning the developmental issue of stability versus change, different theoretical perspectives and theorists, as well as the impact of adulthood and aging on physical, cognitive, and social development.

Application And Comparison

Many theories of aging have described successful aging in terms of avoidance of disease, being actively involved in society, and being able to function well both cognitively and physically (Kinsella & Phillips, 2005). Thus, research findings can be divided into three main areas within adult development: physical, cognitive, and social.

Physical Changes

Many physical changes take place as a person ages. Some of these changes are readily apparent whereas others are not so easily seen. Examples include research on bodily changes, sleep patterns/disturbances in sleep, eating habits, exercise, substance use and abuse, as well as health and disease.

Bodily Changes

Many researchers believe that humans cannot live more than approximately 120 years. This figure seems to be the upper limit of the human life span. Currently, the average life expectancy is far below that number. The average life expectancy in the United States is 77.9 years; women and men born in 2004 have a life expectancy of 80.4 and 75.2 years, respectively. As mentioned earlier, life expectancy has changed significantly over the last century. Although men have always had a lower life expectancy than women, the gap is shrinking. In 1970, the average life expectancy for men was 67.1, and for women, 74.7, a 7.6-year gap. In 1980, the gap was 7.4; in 1990, 7.0; in 2000, 5.4; and today, that gap has narrowed to 5.2 years (U.S. Census Bureau, n.d.).

Throughout adulthood, the body changes physically, with peak body performance reached between 19 and 26 years of age (Schultz & Curnow, 1988). Research has found that (a) compared to young adults, older adults have a 30 percent weaker handgrip force and a 26 percent weaker pinch force (Ranganathan, Siemionow, Sahgal, & Yue, 2001) and (b) older women have slower reaction times than do younger women (Hunter, Thompson, & Adams, 2001). Both genetics and environment influence the rate at which these changes occur. Some research has found that certain markers of aging—motor functioning, mean arterial pressure, and forced expiratory volume—have a strong genetic component (Finkel et al., 2003).

However, despite small physical declines, research also indicates good news with regard to aging. For example, adults can grow new brain cells throughout life (Gould, Reeves, Graziano, & Gross, 1999), and neurons may continue to grow when in enriching environments. In addition, pronounced signs of aging such as grayness, baldness, and facial wrinkles are not predictive of life span (Schnohr, Nyboe, Lange, & Jensen, 1998). Additionally, studies have found that function losses that were once thought to be age-related, such as decreased mobility or memory lapses, can be slowed or even stopped (Shute, 1997). Yet, even with what is known about the aging process, many young, healthy adults often avoid spending time with older people because it reminds them of their future, which they perceive as negative. This negative view of the aging process, although inaccurate in many ways, is propagated by portrayals in the media (Pipher, 2002).


The optimal amount of sleep needed at night and the quality of sleep change during adulthood. Research indicates that eight hours of sleep per night is optimal, resulting in fewer sleep problems than with sleep amounts that are shorter or longer (Grandner & Kripke, 2004). Adults often report experiencing problems with sleep, namely insomnia; one of the most common problems with older adults is initiating or maintaining sleep. These problems can result in interference with daytime functioning, including difficulty concentrating and decreased quality of life (Ancoli-Israel & Ayalon, 2006).

Researchers have investigated sex and age differences with regard to sleep and sleep problems in adulthood. Results indicated that older women report more symptoms of insomnia than do younger women (Liljenberg, Almqvist, Hetta, Roos, & Agren, 1989). Research on age and sleep has found that (a) older adults experience more disturbed sleep in general than do younger adults, (b) older adults may change their perceptions of “acceptable” sleep due to these changes in sleep patterns (Vitielo, Larsen, & Moe, 2004), and (c) the occurrence of nighttime bodily movements in older adults is not related to stage of sleep, as in younger adults (Gori et al., 2004). It is also worth noting that it is not just an individual’s sleep problems that can influence quality of life; if a spouse has sleep problems, he or she can have negative effects on the partner’s health and well-being (Strabridge, Shema, & Roberts, 2004).

Insomnia in adults can be treated in a few ways, such as with benzodiazepines. However, these drugs have known and undesirable side effects (Montgomery, 2002). Ramelteon, a possible new alternative to benzodiazepines, is a melatonin receptor selective agonist that has shown no significant effect on any subjective effect measures, including those related to potential for abuse when compared to a placebo (Johnson, Suess, & Griffiths, 2006). Alternatives to treating insomnia with medications do exist and include cognitive behavioral interventions, bright lights for problems related to timing of sleep, and physiological interventions such as exercise (Montgomery, 2002).

Eating Behaviors

Research indicates that age-related weight gain occurs even among the most active individuals (Williams & Wood, 2006). The implications of these research findings are that weight gain, to some degree, is inevitable during the aging process. Adults can try to reduce weight gain by measures such as healthful eating habits, restricted diet, and exercise. An extreme reaction to weight gain is the development in adults of eating disorders such as anorexia nervosa and bulimia nervosa. At the opposite end of the spectrum, the prevalence of obesity in the United States among adults continues to grow. In 2003 and 2004, obesity rates in adults were as follows: 28.5 percent for ages 20 to 39, 36.8 percent for ages 40 to 59, and 31.0 percent for ages 60 and older (Ogden et al., 2006). In addition, rates of obesity in the elderly (defined as 60 and older) are predicted to increase from 14.6 million in 2000 to 20.9 million in 2010 (Arterburn, Crane, & Sullivan, 2004). Many factors including amount of sleep (Hasler et al., 2004), genetics, and environment (Friedman & Brownell, 1998) are linked to obesity.

Despite the prevalence of eating disorders, there is research demonstrating more positive eating habits in adulthood. For example, research has examined the association between good eating habits and happiness (Doyle & Youn, 2000). One study found that mature adults indicated a preference for high-nutrient foods, whereas fewer than 5 percent of the choices were for dessert (high-sugar) foods (Pierce, Hodges, Merz, & Olivey, 1987). Longitudinal research also indicates that dietary changes occur from adolescence to adulthood, and key factors identified with this change include parents, partners, children, nutritional awareness, employment, and lack of time (Lake et al., 2004). Adults who report eating healthfully say they do so due to concerns over both health benefits and appearance (Hayes & Ross, 1987).


Research documents that exercising regularly is associated with a lower risk of heart disease and an increased life expectancy living compared to not exercising (Lee, Hsieh, & Paffenbarger, 1995). Researchers have found that exercise benefits not only physical health but also mental health, including improved self-concept and reduced anxiety and depression (DiLorenzo et al., 1999; Moses, Steptoe, Mathews, & Edwards, 1989). Exercise is equally important throughout all stages of adulthood. Much research has examined the relation between physical activity and quality of life in older adults. Results consistently find positive outcomes with regard to psychological factors (Alencar et al., 2006; Gitlin et al., 2006; King, Taylor, & Haskell, 1993; McAuley et al., 2006).

Current research on exercise in adults is even investigating the psychological effects of exercise via virtual reality. The results are promising; participants report greater relaxation and less tension than with traditional forms of exercise (Plante, Cage, Clements, & Stover, 2006).

Substance Abuse

Considerable research has documented the use of alcohol and cigarettes by adults. The National Survey on Drug Use and Health (NSDUH) for 2005 asked participants aged 12 and older about alcohol use at three levels: (a) current use, defined as at least one drink in the past 30 days, (b) binge use, defined as five or more drinks on the same occasion on at least one day in the past 30 days, and (c) heavy use, defined as five or more drinks on the same occasion on five or more days in the past 30 days. Results indicated that 51.8 percent of participants reported being current drinkers, 22.7 percent reported binge drinking, and 6.6 percent reported heavy drinking (Substance Abuse and Mental Health Services Administration, 2006). In early adulthood, the rates of alcohol use among college students are also high. For example, nearly 50 percent of college students reported drinking heavily (Johnston, O’Malley, & Bachman, 1996), and binge drinking in college can lead to problems in behavior including missing class, physical injuries, and having unprotected sex (Wechsler, Davenport, Sowdall, Moetykens, & Castillo, 1994).

Some researchers have found sex differences in predictors of heavy drinking in young adulthood. For men, predictors included lower academic functioning, whereas for women, predictors included more frequent sexual behavior and general deviance (Windle, Mun, & Windle, 2005). Research has also examined sex differences with regard to life satisfaction and alcohol consumption. In men, alcohol use was positively related to social satisfaction but not related to other domains of life satisfaction, whereas in women, alcohol use was unrelated to social satisfaction and was related to lower general satisfaction (Murphy, McDevitt-Murphy, & Barnett, 2005). Finally, when investigating issues of alcohol abuse and dependence, men reported all indicators with more frequency than did women, but men were less likely to report indicators that could be seen as weakness such as loss of control (Dawson & Grant, 1993).

Although much research has focused on alcohol use by young adults, alcohol use by mature adults also is a topic of research concern. Research has examined (a) how often mature adults binge drink and (b) what life events influence alcohol consumption. With regard to how often mature adults binge drink, one study found that adults between the ages of 75 and 95 were 15.7 times less likely to binge drink than adults between the ages of 65 and 74. In addition, older women overall were 19.7 times less likely to binge drink than older men (Wiscott, Kopera-Frye, & Begovic, 2002). In a similar study, the NSDUH for 2005 examined rates of current alcohol use (i.e., one drink in the past 30 days) in mature adults and found that 63.7 percent of adults aged 26 to 29, 47.5 percent of adults aged 60 to 64, and 40 percent of adults aged 65 and older were current drinkers (Substance Abuse and Mental Health Services Administration, 2005). Researchers conclude that guidelines for alcohol consumption should be the same for both older men and women (R. H. Moss, Brennan, Schutte, & B. S. Moss, 2004).

In researching links between life events and alcohol consumption, one longitudinal study examined the effects of life events on alcohol consumption in late adulthood. Results indicated that life events such as retirement, marriage, and divorce were associated with drinking. Additionally, there was an association between drinking and these types of life events for individuals with a history of problem drinking (Perreira & Sloan, 2001).

The NSDUH for 2005 also provided data for the use of cigarettes among adults. Over 60 million persons (24.9 percent of the population) were current cigarette smokers. In addition, between 2002 and 2005, cigarette smoking in the past month decreased from 26.0 percent to 24.9 percent (Substance Abuse and Mental Health Services Administration, 2005). Despite the decreased number of smokers, researchers continue to be concerned with rates of smoking due to its association with chronic diseases (Merrill & Verbrugge, 1999) and smoking-related deaths (Bartecchi, Mackenzie, & Schrier, 1995).

Health and Diseases

Of course, one of the biggest issues faced by people as they grow older is health and disease. Most people are not afflicted with regularly occurring health problems; illnesses such as the common cold, flu, or allergies do not impact adults as often as they may have earlier in life. Rather, the older persons become, they more likely they are to be affected by chronic disorders. Chronic disorders are those diseases that are characterized by slow onset and are long in their duration. Chronic disorders usually reveal themselves in middle adulthood (around 40 to 60 years of age) and are different for men and women. Specifically, the most common chronic disorders that occur among women are arthritis, hypertension, and sinus problems; for men, hypertension, arthritis, hearing impairment, and heart disease are the most common.

Even though this is a time when good health prevails for many persons, the onset of mental illness reaches its peak during adulthood (Poa, 2006). One of the most recognizable adulthood mental illnesses is Alzheimer’s disease, a form of dementia that usually affects the older population. Typically, those who are 60 years of age or older are most likely to experience symptoms associated with Alzheimer’s disease, although it does occur in a very small percentage of the younger population. Alzheimer’s disease is characterized by extreme forgetfulness that interferes with daily functioning, such as forgetting people, places, events, everyday activities, and losing the ability to read, write, or even speak (National Institute on Aging, n.d.). One of the largest problems with the onset of Alzheimer’s in late adulthood is diagnosis. Currently, the only sure way to determine if someone is afflicted with this disease is by postmortem examination.

Cognitive Changes

In addition to examining the physical changes in adulthood, research has examined how individuals change with regard to cognition (higher mental processes). When examining cognition during adulthood, research has primarily focused on the evaluation of Jean Piaget’s theory of cognitive development; expertise development; and intelligence, memory, and attention.

Piaget’s Theory of Cognitive Development

Piaget asserted that the last change in cognitive development occurred during the formal operational stage. Piaget thought that during this formal operational stage, which begins at about age 12, thinking becomes abstract and logical. In short, cognitive development becomes mostly complete, although an adult may continue to accumulate life experiences. Despite the popularity of Piaget’s theory, some researchers argue that cognitive development continues past the formal operational stage. Specifically, researchers believe there is an additional stage during which people understand that thought is reflective and that it can vary from situation to situation. Therefore, if people allow emotion to enter into their solution, it will inherently change the properties of thought, leading to unrealistic solutions. This next stage has been referred to as postformal thought (Labouvie-Vief, 2003).

However, some theorists have moved beyond Piaget and a fifth stage by proposing that adult and adolescent thought is inherently different. Schaie and Willis (2000) have argued that change occurs in adults concerning how they use intellect. Particularly, adults apply the information they have gained more than younger individuals do. Likewise, Perry (1970) has argued that adolescents and adults think differently along a quantitative dimension: Adolescents think in very finite ways, with things being either black/white or wrong/right whereas adults are much more reflective and relativistic in their thought process, acknowledging that situations have a lot of grey areas to them and everything cannot be thought of as black/white or wrong/right.

Finally, some theorists have proposed different cognitive models of life span development that have multiple stages in adulthood (Schaie, 1986). This echoes the work done by Piaget but extends cognitive modeling to an entirely different population. In some of these cognitive models, the adult stages include achieving period, social responsibility period, executive period, reorganization period, reintegration period, and legacy period.

Expertise Development

Although much debate has occurred regarding how mental processes change as one gets older, one area of cognition, the development of expertise, appears to be firmly rooted in adult development. As people age, they gain more experience in making decisions. Research indicates that the difference between experts and novices is not due to the amount of information that an expert possesses. Rather, the difference occurs in the use of the information available (Shanteau, 1992). Specifically, experts use far fewer cues when making a judgment than novices do. This ability to narrow down the information needed to make a judgment is achieved only through experience.

Additionally, those who show expertise in an area are capable of making judgments far more quickly than their novice counterparts. Again, this is a skill that is a result of experience. Simply, when novices are faced with a judgment to make, they evaluate all available cues, including those that are irrelevant to the given situation; this takes time. Someone with expertise evaluates only those cues they deem relevant through years of experience; this takes far less time.

However, although people may gain experience in a number of different domains throughout their lives, rarely do they develop expertise in all of these areas; hence, the development of expertise is highly task and domain specific (Weiss & Shanteau, 2006). So, during the aging process, people tend to develop their expertise in specific areas such as careers, relationships, religion, and other areas.

Intelligence, Memory, and Attention

In general, intelligence remains high throughout most of adulthood (Cohen & Swerdlik, 2005). Although there are some cognitive declines during the aging process, these declines occur much later than originally thought (Berg, 2000), are typically more pronounced in intelligence tests requiring speed and motor skills (Finkel, Reynolds, McArdle, & Pedersen, 2005), and can be reduced by remaining active (Lampinen, R. Heikkinen, Kauppinen, & E. Heikkinen, 2006; Mehta, Yaffe, & Covinsky, 2002). In addition, when discussing changes in intellectual abilities during adulthood, a distinction needs to be made between crystallized intelligence and fluid intelligence. Crystallized intelligence comprises acquired knowledge and skills based on life experiences, whereas fluid intelligence comprises problem-solving abilities in novel situations (Cattell, 1963). Previous research has documented that during the aging process crystallized abilities remain stable, but fluid abilities gradually decline (Christensen, 2001; Finkel et al., 2005; Horn & Donaldson, 1980; Li et al., 2004; Schroeder & Salthouse, 2004; Zimprich & Martin, 2002). However, recent research suggests that if results are examined longitudinally rather than cross-sectionally, these declines are minimized (Schaie, 2005). In addition to the traditional way intelligence is defined, some researchers assert that adults continue to develop emotional intelligence, or the ability to understand and manage emotional responses. Goleman (1995) outlined the following four areas of emotional intelligence: developing emotional self-awareness, managing emotions, reading emotions, and handling relationships. Recent research on emotional intelligence investigated sex differences and found that women perform better than men in two of the emotion-related tasks (Austin, 2005).

Mental activities involved in the process of memory include acquisition, retention, and retrieval (Melton, 1963). Two types of declarative memory are episodic memory, memory for the episodes in one’s life, and semantic memory, memory for general knowledge (Tulving, 1989). Results consistently document that episodic memory is subject to significant declines with age, whereas semantic memory remains relatively unaffected (Allen et al., 2005; Hertzog, Dixon, Hultsch, & MacDonald, 2003; Levine, Svoboda, Hay, Winocur, & Moscovitch, 2002; Spaniol, Madden, & Voss, 2006; Wingflied & Kahana, 2002). A recent study investigating sex differences in episodic and semantic memory with age found that women performed better than men on episodic recall and semantic fluency and that these differences were stable over a 10-year time period (de Frias, Nilsson, & Herlitz, 2006).

Social Changes

The final topic is how adults change socially as they develop. Social development includes research on the following topics: family life cycle, sexuality, friendship, and lifestyle choices.

Family Life Cycle

As people age and move from adolescence through adulthood, their place in the family hierarchy changes with them. This progression through the different stages of the family system is often called the family life cycle. Carter and McGoldrick (1989) identified six stages to the family life cycle. During each stage, a person moves through the family hierarchy, assuming the place of someone else who has also moved along the hierarchy. The family life cycle starts with the launching of an individual into the world. This stage is characterized by leaving the security of one’s original family and moving on to start one’s own life. During this time, personal goals, assets, and an individual’s identity formulate. The second stage involves the previously launched individual coming together with another launched individual to create an entirely new family system. The third stage of the family life cycle involves the new couple having children. Here, the new couple moves up a generation in the family hierarchy, assuming the role of parents. Also, all others in their extended families move up a generation as well. The fourth stage is the couple with adolescents. This is a very stressful time in the couple’s life, with their children asserting autonomy and indicating their desire to move up in the family hierarchy. The fifth stage is the couple at midlife. Now the individuals who were launched by their own parents launch their own child. Additionally, this couple is not only still helping their children to manage their lives but also often taking care of their parents, who are now in an elderly state. The final stage is the couple in later life. By this stage, these individuals have launched their child(ren) and, in most cases, have moved up in the family hierarchy to the of grandparent. Although this theory is popular with people who subscribe to stage theory and accounts for the change in the family hierarchy, it has many critics. Specifically, critics of this theory have argued that this theory does not take into account the idea of a multiple family structure or the fact that age and entry into these stages are sometime independent.

The real problem with the family life cycle is that there are relatively few theoretical accounts of family developmental processes in the second half of life. Some researchers have introduced the concept of “family integrity” to account for family changes. “Family integrity” refers to the outcome of an older adult’s development toward meaning, connection, and continuity within his or her multigenerational family (King & Wynne, 2004). Additionally, research has examined those family variables that would possibly explain the differences in family functioning. Research has shown that those variables that contributed substantially to the level of family functioning included family satisfaction, spouse’s satisfaction with sexual relationship, satisfaction with general quality of life, family strengths, flexibility in the way free time is spent in the marital relationship, sound relationships with family and friends, conflict management and resolution, and communication within the marriage (Greeff, 2000).


Everyone knows that sexuality is a part of life. Studies have shown that people who are married or cohabiting engage in the most sexual activity and are more satisfied with sexual activity when compared to people who are single. However, with the increase in sexuality that occurs in adulthood there is an increase in incidences of sexual violence. Nearly 200,000 rapes are reported every year, with far more that go unreported. Research has also shown that 27 percent of college females have experienced unwanted sexual contact ranging from kissing and petting to oral, anal, or vaginal intercourse (Gross, Winslett, Roberts, & Gohm, 2006).

As people age, their interest in sex does not decrease (despite students’ personal beliefs). However, as people get older, certain bodily changes do occur that limit one’s sexual capability. Sometime between the late 40s and early 50s, people experience climacteric, which is a midlife transition in which fertility declines. For women, this occurs in the form of menopause. During this time women experience a dramatic decrease in estrogen production by the ovaries. For men, the effects of climacteric are not as dramatic. Most men see a modest decline in hormone levels during middle and late adulthood. However, this modest decline can lead to difficulty in achieving erections, also known as erectile dysfunction (Crooks & Bauer, 2002). As a person moves into late adulthood, sexuality continues. Yet, due to decreases in body functioning, the occurrences become less frequent. Both men and women begin having trouble achieving orgasm. Still, research indicates that although sexual functioning decreases, sexual desire remains (Johnson, 1996). One study showed that nearly half of all Americans over the age of 60 have sexual relations at least once per month and 40 percent would like to have it more often (Koch & Mansfield, 2001/2002).


Friendships are important throughout all stages of development. Friends serve many functions in adulthood, including fostering a sense of well-being, serving as social support (Hartup & Stevens, 1999), and bolstering self-esteem (Bagwell et al., 2005). During adulthood the importance of and reliance on friends changes depending on the phase of adulthood one is in. For example, individuals in the single phase of adulthood rely on friends to satisfy social needs significantly more than do individuals in the married-without-children phase and the parenthood phase (Carbery & Buhrmester, 1998). Friendships continue to serve a social function well into late adulthood. Research examining the structure of older adult friendship networks indicates that three factors (i.e., egalitarianism, sociability, and religiosity) underlie the network structure (Adams & Torr, 1998).

The bulk of research on friendships in adulthood has been conducted on sex differences in adulthood friendships. Traditionally, research has indicated that women typically engage in more self-disclosure with same-sex friends, whereas men typically engage in shared activities with same-sex friends (Antonucci, 1990). Sex differences have also been researched with regard to conversing with friends; women use conversation to provide social support and listen, whereas men use conversation to solve problems and fix situations (Tannen, 1990). Recent research has indicated that men and women report equal amounts of self-disclosure (Radmacher & Azmitia, 2006) and willingness to trust a friend (Roy, Benenson, & Lilly, 2000). However, sex differences were found, with self-disclosure predicting emotional closeness for women and men and shared activities predicting emotional closeness for men only (Radmacher & Azmitia, 2006).

Research has examined other topics with regard to adult friendships. These topics include how age influences relationship satisfaction, the stages in friendships at the workplace, and how financial status influences friendships. Results on these topics indicate more positive outcomes for friendships of similar ages (Holladay & Kerns, 1999) and three primary transitions when moving from acquaintances to close friends in the workplace (Sias & Cahill, 1998). Finally, results indicate that friendship patterns differ between working-class and middle-class men and women. Specifically, working-class men and women have friendships with a high degree of reciprocity and interdependence with regard to material goods and services, whereas middle-class men and women have friendships with shared leisure and social networks (Walker, 1995).

Lifestyle Choices

There are many different types of lifestyles that adults choose. Lifestyle choices include (a) single, (b) cohabiting, (c) gay and lesbian, (d) divorced, and (e) married. Each of the possible lifestyle choices has its advantages and disadvantages, with much research exploring each.

A new trend in the United States is to stay single longer into adulthood. This is evident in data that shows the average age of first marriage is being delayed. Currently, men and women typically do not get married until the ages of 27 and 25, respectively (U.S. Census Bureau, n.d.). Traditionally, being single was viewed as a negative; however, many people are seeing the benefits of such a lifestyle. Some advantages of being single include having greater autonomy, privacy, and the ability to develop personal resources.

Likewise, another growing trend in the United States is the cohabiting relationship, in which people live together in a sexual relationship but are not married (Crooks & Bauer, 2002). Although this lifestyle type is increasing (approximately 7 percent of adult population), it is typically short-lived, with most such relationships not lasting longer than one year (Hyde & Delamater, 1999). Additionally, research indicates that cohabiting couples have a long list of financial and relationship prerequisites they believe must be met in order for them to wed (Gibson-Davis, Edin, & McLanahan, 2005; McGinnis, 2003). Research also shows that those who eventually do get married after cohabiting have lower marital satisfaction than those who are married and do not cohabitate (Booth & Johnson, 1988). One of the biggest difficulties in a cohabiting relationship is the ending of that relationship. Often, those who engage in a cohabiting lifestyle share wealth, resources, and goods with the other person, and when the relationship ends, the dividing up of these things becomes problematic.

Of course, many people who do marry later regret their decision and divorce. Studies show that divorce is most likely to occur between the 5th and 10th years of marriage (National Center for Health Statistics, 2000). Research conducted to determine what factors predicted divorce or marital stability shows that couples who eventually divorce were low in fondness for their partners, high in negativity, low in “we-ness,” high in chaos, low in glorifying the struggle, and high in disappointment in the marriage (Buehlman, Gottman, & Katz, 1992). Research also shows that people who are divorced have far more psychological and physical problems than do married people, including higher rates of psychiatric disorders, higher rates of admission to psychiatric hospitals, clinical depression, substance abuse, and psychosomatic problems such as sleeping disorders. However, the biggest problem is that people who divorce no longer trust others romantically (Hetherington & Stanley-Hagan, 1995).

Recently in this country a lot of attention has focused on gay and lesbian couples. Despite popular misconceptions, research shows that homosexual and heterosexual couples have very similar relationships. Specifically, homosexual couples are similar to heterosexual couples in satisfaction, love, joys, and conflicts (Hyde & DeLamater, 1999; Peplau, Veniegas, & Campbell, 1996). Additionally, homosexuals tend to seek long-term relationships rather than short-term relationships (Peplau, 1991; Peplau & Spalding, 2000) and gender roles do not always take place (Patterson, 2000). However, a homosexual lifestyle brings with it the same barriers to ending the relationship that a cohabitating lifestyle does (Peplau & Spalding, 2000).

The final type of lifestyle choice a person can make is to be married. The average marriage lasts nine years and is more difficult today than it was 25 years ago due to increased equality and changing norms (Christiansen & Pasch, 1993). An update to a longitudinal study of marriage role expectations that began in 1961 echoed this thought by showing that there was a significant shift toward more egalitarian expectations over the past 40 years (Botkin, Weeks, & Morris, 2000).

In order to make a marriage last longer than nine years, research indicates that communication and sexual satisfaction are important. Research also shows that sexual satisfaction partially compensates for the negative effects of poor communication (Litzinger & Gordon, 2005). Additionally, gender ideology plays a role in the longevity of marriages. Studies indicate that, for men, those who hold egalitarian attitudes report significantly higher levels of marital happiness than those with more traditional attitudes (Kaufman & Taniguchi, 2006). For women, research suggests that the marital bond serves as a perceptual filter through which they evaluate their husbands’ behavior either positively or negatively (Hawkins, Carrere, & Gottman, 2002). Finally, older couples with long-term marriages indicated that marital satisfaction and longevity are a result of (a) reduced potential for conflict and greater potential for pleasure in several areas including children, (b) equivalent levels of overall mental and physical health, and (c) fewer gender differences in sources of pleasure (Levenson, Cartensen, & Gottman, 1993).


Although the history of developmental psychology has primarily focused on child and adolescent development, research on adulthood and aging has produced a wealth of findings, as evidenced by this chapter. Development does not cease at a magic age; rather, adults continue to mature and develop in physical, cognitive, and social ways. With increased attention to adult development, the future of research continues to be promising. Simply, research exploring this area will be needed as the elderly population continues to grow; because of this fact, opportunities will always arise to examine development over the course of the entire life span.


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