Adult development encompasses the changes that occur in biological and psychological domains of human life from the end of adolescence until the end of one's life. Changes occur at the cellular level and are partially explained by biological theories of adult development and aging.[1] Biological changes influence psychological and interpersonal/social developmental changes, which are often described by stage theories of human development. Stage theories typically focus on "age-appropriate" developmental tasks to be achieved at each stage. Erik Erikson and Carl Jung proposed stage theories[2][3] of human development that encompass the entire life span, and emphasized the potential for positive change very late in life.
The concept of adulthood has legal and socio-cultural definitions. The legal definition[4] of an adult is a person who is fully grown or developed. This is referred to as the age of majority, which is age 18 in most cultures, although there is a variation from 15 to 21. The typical perception of adulthood is that it starts at age 18, 21, 25 or beyond. Middle-aged adulthood, starts at about age 40, followed by old age/late adulthood around age 65. The socio-cultural definition of being an adult is based on what a culture normatively views as being the required criteria for adulthood, which in turn, influences the lives of individuals within that culture. This may or may not coincide with the legal definition.[5] Current views on adult development in late life focus on the concept of successful aging, defined as "...low probability of disease and disease-related disability, high cognitive and physical functional capacity, and active engagement with life."[6]
Biomedical theories hold that one can age successfully by caring for physical health and minimizing loss in function, whereas psychosocial theories posit that capitalizing upon social and cognitive resources, such as a positive attitude or social support from neighbors, family, and friends, is key to aging successfully.[7] Jeanne Louise Calment exemplifies successful aging as the longest living person, dying at 122 years old. Her long life can be attributed to her genetics (both parents lived into their 80s), her active lifestyle and an optimistic attitude.[8][9] She enjoyed many hobbies and physical activities, and believed that laughter contributed to her longevity. She poured olive oil on all of her food and skin, which she believed also contributed to her long life and youthful appearance.[10]
Adult development is a somewhat new area of study in the field of psychology. Previously it was assumed that development would cease at the end of adolescence. Further research has concluded that development continues well after adolescence and into late adulthood. This new field of research was influenced by the aging population of the "baby boomer" generation.[11] The population of Americans who are the age of 65 or over was at roughly 9 million in 1940. In just 60 years that total has grown to over 35 million people. This rise in population and life expectancy had shined a light on the manifestation of development throughout adulthood.[12] Changes in adulthood have been described by several theories and metatheories, which serve as a framework for adult development research. One of which is Erik Erikson who went beyond childhood stages and introduced the concept of continuing development until death.[13]
Life span development can be defined as age-relating experiences that occur from birth to the entirety of a human's life. The theory considers the lifelong accumulation of developmental additions and subtractions, with the relative proportion of gains to losses diminishing over an individual's lifetime.[14] According to this theory, life span development has multiple trajectories (positive, negative, stable) and causes (biological, psychological, social, and cultural). Individual variation is a hallmark of this theory – not all individuals develop and age at the same rate and in the same manner.[15]
Bronfenbrenner's ecological theory
Urie Bronfenbrenner's ecological theory is an environmental system theory and social ecological model which focuses on five environmental systems:
Jeffrey Arnett's theory of Emerging Adulthood
The theory of Emerging Adulthood was developed by Jeffery Arnett in the early 2000s. The theory is centered around changes often experienced during the transition from adolescence to adulthood. This time period takes place usually between the ages of 18 and 29.[18] The concept of emerging adulthood is new, and likely developed due to growing numbers of college attendance and other social, economic, and cultural changes that have delayed typical markers of being an "adult"[2].
There are five main characteristics describing what Emerging Adulthood looks like. To examine these five characteristics, in 1995 Jeffery Arnett interviewed 300 young adults aged 18 to 29 on the topic of what they wanted out of life.[19] Due to this, Jeffery Arnett came up with the five characteristic and they go as follows: The Age Of Identity Exploration, The Age of Instability, The Age of Self Focus, The Age of Feeling in Between, and The Age of Possibilities. The Age Of Identity Exploration is one that Arnett found to be the most prevalent in the young people's lives, due to most people at this stage trying to figure out what they want in life and what their values are in life.[19] The Age of Instability is where one comes into the area of life where everything is going to be changing frequently and some of the things that change dramatically are the status of ones love life and schooling. When one is in this stage of life, they have not yet established themselves, who they want to become, and what their career will look like. Many see this time of life in a negative light but it is where you can obtain the foundation to what you're future will be.[19] The Age of Self Focus is the time where you start to decide who you are and what you want to become. This is where the individual will work a lot harder on themselves and begin to see significant personal growth, and will also become far more independent and self motivated.[19] The Age of Feeling in Between stage is where one is in an area of life when you cannot do everything on your own but are starting to move away from being under the rule of your parents.[19] The Age of Possibilities is the stage where many emerging adults have many different futures ahead of them and a sense of optimism for the different opportunities life has to offer. In addition to, this stage any emerging adults believe that they have the opportunity to have better lives than what their parents had before them.[19] Some emerging adults in America between the ages of 18 and 25 when asked if they were adults, were unable to give a definitive answer of "yes" or "no" but more than likely give the answer that "yes, they have aspects of being an adult but they also have aspects of not being an adult yet."[20] Overall, there is much to the theory of Emerging Adulthood but it still has criticism about its legitimacy.[21] There are some that say that the theory neglects other classes and that this is a flaw.[22] Some of the other things that have been stated about this theory is that it is steered too much to our time period and that this can be viewed as a major flaw and that it also focuses too much on Western culture as well.[23]
Erik Erikson developed stages of ego development that extended through childhood, adolescence, and adulthood. He was trained in psychoanalysis and was highly influenced by Freud, but unlike Freud, Erikson believed that social interaction is very important to the individual's psychosocial development. His stage theory consists of 8 stages in life from birth to old age, each of which is characterized by a specific developmental task.[13] During each stage, one developmental task is dominant, but may be carried forward into later stages as well. According to Erikson, individuals may experience tension when advancing to new stages of development, and seek to establish equilibrium within each stage. This tension is often referred to as a "crisis," a psycho-social conflict, in which an individual experiences conflict between their inner and outer worlds that are relative to whichever stage they are in.[24] If equilibrium is not found for each task there are potential negative outcomes called maladaptations (abnormally positive) and malignancies (abnormally negative), where malignancy is worse of the two.[24] It posits eight sequential stages of individual human development influenced by biological, psychological, and social factors throughout the lifespan. This bio-psychosocial approach has influenced several fields of study, including gerontology, personality development, identity formation, life cycle development, and more. [3]
Trust vs. Mistrust is experienced in the first years of life. Trust in infancy helps the child be secure about the world around them. Because an infant is completely dependent, they start building trust based on the dependability and quality of their caregivers. If a child successfully develops trust, he or she will feel safe and secure.
Maladaptation – sensory distortion (e.g. unrealistic, spoilt, deluded)
Malignancy – withdrawal (e.g. neurotic, depressive, afraid)
After gaining trust in their caregivers, infants learn that they are responsible for their actions. They begin to make judgments and move on their own. When toddlers are punished too severely or too often, they are likely to experience shame and self-doubt.
Maladaptation – impulsivity (e.g. reckless, inconsiderate, thoughtless)
Malignancy – compulsion (e.g. anal, constrained, self-limiting)
During preschool years children start to use their power and control over the world through playing and other social interactions. Children who successfully pass this stage feel capable and able to lead others, while those who do not are left with a sense of guilt, self-doubt, and lack of initiative.
Maladaptation – ruthlessness (e.g. exploitative, uncaring, dispassionate)
Malignancy – inhibition (e.g. risk-averse, unadventurous)
When children interact with others they start to develop a sense of pride in their abilities and accomplishments. When parents, teachers, or peers command and encourage kids, they begin to feel confident in their skills. Successfully completing this stage leads to a strong belief in one's ability to handle tasks set in front of them.
Maladaptation – narrow virtuosity (e.g. workaholic, obsessive, specialist)
Malignancy – inertia (e.g. lazy, apathetic, purposeless)
During adolescent years, children begin to find out who they are. They explore their independence and develop a sense of self. This is Erikson's fifth stage, Identity vs Confusion. Completing this stage leads to fidelity, an ability that Erikson described as useful to live by society's standards and expectations.[25]
Maladaptation – fanaticism (e.g. self-important, extremist)
Malignancy – repudiation (e.g. socially disconnected, cut-off)
In early adulthood, individuals begin to experience intimate relationships in which they must either commit to relating and connecting to others on a personal level or retreat into isolation, afraid of commitment or vulnerability. Being intimate with someone does not always mean having a sexual component; in a platonic relationship, closeness might take the form of self-disclosure. After reaching this stage, a person is equipped to build strong, enduring relationships with other people.[26] According to psychologist Robert Sternberg's "Triangular Theory of Love,[27]" companionate love is founded on deep affection, trust, and commitment and develops over time and becomes more prominent in long-term partnerships. In contrast, passionate love is characterized by intense feelings, physical attraction, and excitement and is usually present at the beginning of a relationship. Both types of love are thought to be distinct types that can coexist within a relationship.
Maladaptation – promiscuity (e.g. sexually needy, vulnerable)
Malignancy – exclusivity (e.g. loner, cold, self-contained)
This stage usually begins when an individual has established a career and has a family. In this stage, an individual must either contribute significantly to their careers, families and communities in order to ensure success in the next generation or they stagnate, creating a threat to their well-being which can be referred to as a "mid-life crisis." When individuals feel they have successfully fostered growth in themselves and their relationships, they will feel satisfied in their successes and contributions to the world.[28]
Maladaptation – overextension (e.g. do-gooder, busy-body, meddling)
Malignancy – rejectivity (e.g. disinterested, cynical)
This stage often occurs when an older individual is in retirement and expecting the end of their life. They reflect on their life and either come to the conclusion that they have found meaning and peace, or their lives were not fulfilling, and they didn't achieve what they wanted to. The former is self-accepting of who they've become, while the latter is not accepting of themselves or their circumstances in life, which leads to despair.[29]
Maladaptation – presumption (e.g. conceited, pompous, arrogant)
Malignancy – disdain (e.g. miserable, unfulfilled, blaming)
Michael Commons's Model of Hierarchical Complexity (MHC) is an enhancement and simplification of Bärbel Inhelder and Jean Piaget's developmental model. It offers a standard method of examining the universal pattern of development. This model of hierarchical complexity explains development in stages that are not connected to a person's age, but on the ability of the person to complete increasingly complex hierarchical tasks. For one task to be more hierarchically complex than another, the new task must meet three requirements: 1) It must be defined in terms of the lower stage actions; 2) it must coordinate the lower stage actions; 3) it must do so in a non-arbitrary way. The following are the Common's 15 stages of development which demonstrate the increasingly complex nature of development.
Carl Jung, a Swiss psychoanalyst, formulated four stages of development and believed that development was a function of reconciling opposing forces.[32]
Daniel Levinson's theory, influenced by Erikson's theory of development, explain a set of psychosocial 'seasons' through which adults must pass as they move through early adulthood and midlife. Each of these seasons is characterized by a crisis to overcome. Stages are created by the challenges of building or maintaining a life structure and by the social norms that apply to particular age groups, particularly concerning relationships and career.[36] Levinson also emphasized that a common part of adult development is the midlife crisis. The process that underlies all these stages is individuation - a movement towards balance and wholeness over time. The key stages that he discerned in early adulthood and midlife were as follows:
Levinson's work includes research on differences in the lives of men and women. He published The Seasons of a Man's Life and The Seasons of a Woman's Life, with findings that men and women went through essentially the same crises but differed in "The Dream." The author wrote that men's dreams are centered around occupations and women's are conflicted between occupation and marriage and family.[38][39]
The 'biopsychosocial' approach to adult development states that to understand human development in its fullness, biological, psychological, and social levels of analysis must be included. There are a variety of biopsychosocial meta-models, but all entail a commitment to the following four premises:
Robert Kegan is an American developmental psychologist as well as the author or co-author of books such as In Over Our Heads,[41] The Evolving Self,[42] How the Way We Talk Can Change the Way We Work,[43] and An Everyone Culture: Becoming a Deliberately Developmental Organization[44] among other works. Kegan was also a professor at Harvard Graduate School of Education.
In The Evolving Self, Kegan explores human life problems through meaning-making, the process of making sense of experience by discovering problems and resolving problems. This book assists professional helpers with ways to understand how their clients make sense of their problems.[42] Kegan proposes a framework of six evolutionary balances (developmental stages) that each have a culture of embeddedness. The culture of embeddedness can be examined in terms of three functions in development: confirmation (holding on), contradiction (letting go), and continuity (staying put).[42] In this book, Kegan describes the process of emergence for the six evolutionary balances. These evolutionary balances have analogues to theories from Piaget, Kohlberg, Loevinger, Maslow, McClelland/Murray, and Erikson.[42] In Over Our Heads further elaborates Kegan's perspective on adult development.[41]
The book How the Way We Talk Can Change the Way We Work presents a practical method called the "immunity map" to help people overcome an immunity to change, an obstacle to further psychological development.[43] The map is made of a four-column worksheet that guides a process of self-reflective inquiry.
The book An Everyone Culture: Becoming a Deliberately Developmental Organization Kegan and colleagues connect the concept of deliberately developmental organizations (DDOs) with adult development theories and argues for the importance of transitioning from a socialized mind to a self-authoring mind and then from a self-authoring mind to a self-transforming mind.[44]
Physical development in midlife and beyond include changes at the biological level (senescence) and larger organ and musculoskeletal levels. Sensory changes and degeneration begin to be common in midlife. Degeneration can include the breakdown of muscle, bones, and joints. Which leads to physical ailments such as sarcopenia or arthritis.[45]
At the sensory level, changes occur to vision, hearing, taste, touch, and smell. Two common sensory changes that begin in midlife include our ability to see close objects and our ability to hear high pitches.[46][47] Other developmental changes to vision might include cataracts, glaucoma, and the loss of central visual field with macular degeneration.[48] Hearing also becomes impaired in midlife and aging adults, particularly in men. In the past 30 years, hearing impairment has doubled.[49] Hearing aids as an aid for hearing loss still leave many individuals dissatisfied with their quality of hearing. Changes in olfaction and sense of taste can co-occur. "Olfactory dysfunction can impair quality of life and may be a marker for other deficits and illnesses" and can also lead to decreased satisfaction in taste when eating. Losses to the sense of touch are usually noticed when there is a decline in the ability to detect a vibratory stimulus. The loss of sense of touch can harm a person's fine motor skills such as writing and using utensils. The ability to feel painful stimuli is usually preserved in aging, but the process of decline for touch is accelerated in those with diabetes.[48]
Physical deterioration to the body begins to increase in midlife and late life, and includes degeneration of muscle, bones, and joints. Sarcopenia, a normal developmental change, is the degeneration of muscle mass, which includes both strength and quality.[50] This change occurs even in those who consider themselves athletes, and is accelerated by physical inactivity.[51] Many of the contributing factors that may cause sarcopenia to include neuronal and hormonal changes, inadequate nutrition, and physical inactivity.[50] Apoptosis has also been suggested as an underlying mechanism in the progression of sarcopenia. The prevalence of sarcopenia increases as people age and is associated with the increased likelihood of disability and restricted independence among elderly people. Approaches to preventing and treating sarcopenia are being explored by researchers. A specific preventive approach includes progressive resistance training, which is safe and effective for the elderly.[52]
Developmental changes to various organs and organ systems occur throughout life. These changes affect responses to stress and illness, and can compromise the body's ability to cope with the demand for organs.[53] The altered functioning of the heart, lungs, and even skin in old age can be attributed to factors like cell death or endocrine hormones. There are changes to the reproductive system in midlife adults, most notably menopause for women, the permanent end of fertility. In men, hormonal changes also affect their reproductive and sexual physiology, but these changes are not as extreme as those experienced by women.[54]
As adult bodies undergo a variety of physical changes that cause health to decline, a higher risk of contracting a variety of illnesses, both physical and mental, is possible.[55]
Scientists have made a distinctive connection between aging and cancer. It has been shown that the majority of cancer cases occur in those over 50 years of age.[56] This may be due to the decline in the strength of the immune system as one ages or to co-existing conditions. There a variety of symptoms associated with cancer, commonly growths or tumors may be indicators of cancer. Radiation, chemotherapy, and in some cases, surgery, is used to treat cancer.
Osteoarthritis is one of the most commonly experienced illnesses in adults as they age. Although there are a variety of types of arthritis they all include very similar symptoms: aching joints, stiff joints, continued joint pain, and problems moving joints.[61]
It has been found that older age does increase the risk factor of contracting cardiovascular disease. Hypertension and high cholesterol have also been found to increase the likelihood of acquiring cardiovascular disease, which is also commonly found in older adults. Cardiovascular diseases include a variety of heart conditions that may induce a heart attack or other heart-related problems. Healthy eating, exercise, and avoiding smoking are usually used to prevent cardiovascular disease.
Infection occurs more easily as one ages, as the immune system starts to slow and become less effective. Aging also changes how the immune system reacts to infection, making new infections harder to detect and attack. Essentially, the immune system has a higher chance of being compromised the older one gets.[62]
A chronic illness that effect body processes glucose. It becomes far more prevalent in those over 45. Both type 1 and type 2 diabetes may lead to the following serious illnesses such as; strokes, heart attacks, nerve damage, kidney damage and blindness.
New neurons are constantly formed from stem cells in parts of the adult brain throughout adulthood, a process called adult neurogenesis. The hippocampus is the area of the brain that is most active in neurogenesis. Research shows that thousands of new neurons are produced in the hippocampus every day.[63] The brain constantly changes and rewires itself throughout adulthood, a process known as neuroplasticity. Evidence suggests that the brain changes in response to diet, exercise, social environment, stress, and toxin intake. These same external factors also influence genetic expression throughout adult life - a phenomenon known as genetic plasticity.[64]
Dementia is characterized by persistent, multiple cognitive deficits in the domains including, but not limited to, memory, language, and visuospatial skills and can result from central nervous system dysfunction.[65][66][67] Two forms of dementia exist: degenerative and nondegenerative. The progression of nondegenerative dementias, like head trauma and brain infections, can be slowed or halted but degenerative forms of dementia, like Parkinson's disease, Alzheimer's disease, and Huntington's are irreversible and incurable.
Alzheimer's disease (AD) was discovered in 1907 by Dr. Alois Alzheimer, a German neuropathologist and psychiatrist.[68] Physiological abnormalities associated with AD include neurofibrillary plaques and tangles. Neuritic plaques, that target the outer regions of the cortex, consist of withering neuronal material from a protein, amyloid-beta. Neurofibrillary tangles, paired helical filaments containing over-phosphorylated tau protein, are located within the nerve cell. Early symptoms of AD include difficulty remembering names and events, while later symptoms include impaired judgment, disorientation, confusion, behavior changes, and difficulty speaking, swallowing, and walking. After initial diagnosis, a person with AD can live, on average, an additional 3 to 10 years with the disease.[69] In 2024, it was estimated that 6.9 million Americans age 65 and older had AD.[70] Environmental factors such as head trauma, high cholesterol, and type 2 diabetes can increase the likelihood of AD.[71]
The impact of Alzheimer's disease on individuals and their families is profound, making ongoing research and promising developments in treatments like lecanemab incredibly important. The strides being made in understanding the physiological aspects of the disease, as well as the potential treatments, provide hope for millions of people worldwide who are affected by Alzheimer's. It's heartening to hear about the progress in clinical trials for lecanemab and the possibility it holds for mitigating the early symptoms of cognitive decline. Continued investment in research and support for those living with Alzheimer's is crucial as we work towards a future where effective treatments and, ultimately, a cure can improve the lives of those impacted by this devastating condition.
Recent studies for the drug lecanemab have shown promising results for people who suffer from Alzheimer's disease. The drug has been approved for phase three clinical trials[1]. This medication treats early symptoms of cognitive deterioration in people with Alzheimer's.
Huntington's disease (HD) named after George Huntington is a disorder that is caused by an inherited defect in a single gene on chromosome 4, resulting in a progressive loss of mental faculties and physical control.[72][73] HD affects personality, leads to involuntary muscle movements, cognitive impairment, and deterioration of the nervous system.[74][75] Symptoms usually appear between the ages of 30 and 50 but can occur at any age, including adolescence.[73] There is currently no cure for HD and treatments focus on managing symptoms and quality of life. Current estimates claim that 1 in 10,000 Americans have HD, however, 1 in 250,000 are at-risk of inheriting it from a parent.[76] Most individuals with HD live 10 to 20 years after a diagnosis.
Parkinson's disease (PD) was first described by James Parkinson in 1817.[77] James Parkinson did describe his first findings of Parkinson's disease (PD) in early essays.[78] It typically affects people over the age of 50 and affects about 0.3% of developed populations.[79] PD is related to damaged nerve cells that produce dopamine.[80] Common symptoms experienced by people with PD include trembling of the hands, arms, legs, jaw, or head; rigidity (stiffness in limbs and the midsection); bradykinesia; and postural instability, leading to impaired balance and/or coordination.[81][8