Adulthood is the stage of development that begins around 18 to 21 years and ends at death. Because physical change slows from a gallop to a crawl, many of us think of adulthood as the destination to which the process of development finally delivers us, and that once we’ve arrived, our journey is pretty much complete. Nothing could be further from the truth. A whole host of physical, cognitive, and emotional changes take place between our first legal beer and our last legal breath.

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The early 20s are the peak years for health, stamina, vigor, and prowess, and because our psychology is so closely tied to our biology, these are also the years during which most cognitive abilities are sharpest. At this very moment, you probably see farther, hear better, and remember more accurately than you ever will again. Enjoy it. Somewhere between the ages of 26 and 30, you will begin the slow and steady decline that will not end until you do. Just 10 or 15 years after puberty, your body will begin to break down in almost every way. Your muscles will be replaced by fat, your skin will become less elastic, your hair will thin and your bones will weaken, your sensory abilities will become less acute, and your brain cells will die at an accelerated rate. Eventually, if you are a woman, your ovaries will stop producing eggs, and you will become infertile. Eventually, if you are a man, your erections will be softer and fewer and farther between. Indeed, other than being more resistant to colds and less sensitive to pain, your elderly body just won’t work as well as your youthful body does.

But don’t worry, the news gets worse. Because as these physical changes accumulate, they will begin to have measurable psychological consequences (Salthouse, 2006; see FIGURE 10.12). For instance, as you age, your prefrontal cortex will deteriorate more quickly than the other areas of your brain (Raz, 2000), and you will experience a noticeable decline on cognitive tasks that require effort, initiative, or strategy. Although your memory will worsen in general, you will experience more decline in working memory (the ability to hold information “in mind”) than in long-term memory (the ability to retrieve information), and more decline in episodic memory (the ability to remember particular past events) than in semantic memory (the ability to remember general information such as the meanings of words).

But not all the news is bad. Even though your cognitive machinery will get rustier, research suggests that you will partially compensate by using it much more skillfully (Bäckman & Dixon, 1992; Salthouse, 1987). Older chess players remember chess positions much more poorly than younger players do, but they play just as well because they learn to search the board more efficiently (Charness, 1981). Older typists react more slowly than younger typists do, but they type just as quickly and accurately because they are better at anticipating the next word in spoken or written text (Salthouse, 1984). All of this suggests that older adults are using the skills they developed over a lifetime to compensate for the age-related declines they experience in memory and attention (Park & McDonough, 2013).

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Even the brain changes the way it does business. As you know from the Neuroscience and Behavior chapter, brains are differentiated—that is, they have different parts that do different things. But as they age, brains become de-differentiated (Lindenberger & Baltes, 1994), and parts that once worked like independent specialists start to pull together as a team (Park & McDonough, 2013). For example, when young adults try to keep verbal information in working memory, the left prefrontal cortex is more strongly activated than the right, and when they try to keep spatial information in working memory, the right prefrontal cortex is more strongly activated than the left (Smith & Jonides, 1997). But this bilateral asymmetry pretty much disappears in older adults, which suggests that the older brain is compensating for the declining abilities of one half by calling on the other half to help out (Cabeza, 2002; see FIGURE 10.13). The physical machinery breaks down as time passes, and one of the ways in which the brain rises to that challenge is by changing its division of labor.

So one reason why Grandpa can’t find his car keys is that his prefrontal cortex doesn’t work as well as it used to. But another reason is that the location of car keys just isn’t the sort of thing that grandpas spend their precious time memorizing (Haase, Heckhausen, & Wrosch, 2013). According to socioemotional selectivity theory (Carstensen & Turk-Charles, 1994), younger adults are largely oriented toward the acquisition of information that will be useful to them in the future (e.g., reading reviews of new technology), whereas older adults are generally oriented toward information that brings emotional satisfaction in the present (e.g., reading poems and novels). Because young people have such long futures, they invest their time attending to, thinking about, and remembering information that they may want to use tomorrow. Because older people have much shorter futures, they spend their time attending to, thinking about, and remembering positive information that they can enjoy today.

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That’s one of the reasons why older people are much worse than younger people when they try to remember a series of unpleasant faces (see FIGURE 10.14), but only slightly worse when they try to remember a series of pleasant faces (Mather &Carstensen, 2003). Indeed, compared to younger adults, older adults are generally better at sustaining positive emotions and curtailing negative ones (Isaacowitz, 2012; Isaacowitz & Blanchard-Fields, 2012; Lawton et al., 1992; Mather & Carstensen, 2005). They also experience fewer negative emotions (Carstensen et al., 2000; Charles, Reynolds, & Gatz, 2001; Mroczek & Spiro, 2005; Schilling, Wahl, & Wiegering, 2013), and are more accepting of them when they do (Shallcross et al., 2013). Given all this, you shouldn’t be surprised to learn that late adulthood is consistently reported to be one of the happiest and most satisfying periods of life (see FIGURE 10.15). You shouldn’t be surprised, but you probably are because young adults vastly overestimate the problems of aging (Pew Research Center for People & the Press, 2009).

Because having a short future orients people toward emotionally satisfying rather than intellectually profitable experiences, older adults become more selective about their interaction partners, choosing to spend time with family and a few close friends rather than with a large circle of acquaintances. One study monitored a group of people from the 1930s to the 1990s and found that the rate of interaction with acquaintances declined from early to middle adulthood, but the rate of interaction with spouses, parents, and siblings remained stable or increased (Carstensen, 1992). “Let’s go meet some new people” isn’t something that most 60-year-olds tend to say, but “Let’s go hang out with some old friends” is. It is sad but instructive to note that many of the cognitive and emotional changes that characterize older adults are also observed among younger adults whose futures have been shortened by terminal illness (Carstensen & Fredrickson, 1998).

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The psychological separation from parents that begins in adolescence usually becomes a physical separation in adulthood. In virtually all human societies, young adults leave home, get married, and have children of their own. The average college-age American is likely to get married at around the age of 27, have approximately 1.8 children, and consider both partner and children to be sources of great joy.

But do marriage and children really make us happy? Research shows that married people live longer, have more frequent sex (and enjoy that sex more), and earn several times as much money as unmarried people do (Waite, 1995). Given these differences, it is no surprise that married people report being happier than unmarried people—whether those unmarried people are single, widowed, divorced, or cohabiting (Johnson & Wu, 2002). That’s why many researchers consider marriage one of the best investments individuals can make in their own happiness. But other researchers suggest that married people may be happier because happy people may be more likely to get married and that marriage may be the consequence—and not the cause—of happiness (Lucas et al., 2003). The general consensus among scientists seems to be that both of these positions have merit: Even before marriage, people who end up married tend to be happier than those who never marry, but marriage does seem to confer further benefits.

Children are another story. In general, research suggests that children do not increase their parents’ happiness, and may even decrease it (DiTella, MacCulloch, & Oswald, 2003; Simon, 2008; Senior, 2014). For example, parents typically report lower marital satisfaction than do nonparents—and the more children they have, the less satisfaction they report (Twenge, Campbell, & Foster, 2003). Studies suggest that marital satisfaction starts out high, dips down at about the time that the children are in diapers, begins to recover, dips again when the children are in adolescence, and returns to its premarital levels only when children leave home (see FIGURE 10.16). Given that mothers typically do more child care than fathers, it is little wonder that the negative impact of parenthood is stronger for women than for men. Women with young children are especially likely to experience role conflicts (“How am I supposed to manage being a full-time lawyer and a full-time mother?”) and restrictions of freedom (“I never get to play tennis anymore”). One study found that American women were less happy when taking care of their children than when eating, exercising, shopping, napping, or watching television—and only slightly happier than when they were doing housework (Kahneman et al., 2004).

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Does all of this mean that people would be happier if they didn’t have children? Not necessarily. Because researchers cannot randomly assign people to be parents or nonparents, studies of the effects of parenthood are necessarily correlational. People who want children and have children may be somewhat less happy than people who neither want them nor have them, but it is possible that people who want children would be even less happy if they didn’t have them. What does seem clear is that raising children is a challenging job that people find most rewarding when they’re not in the middle of doing it.