Emerging Adults
PSYC 210-B04: Developmental Psychology
Jennifer Kennedy
March 1, 2021
Emerging Adults
Emerging adulthood has roughly been proposed as a new stage of life that is between adolescence and
young adulthood, lasting roughly from ages 18 to 25. “Emerging Adulthood” is a term used to describe
that development spanning age from 18 to 25. Emerging adults can be described as the time from the
end of adolescence to the time of young-adult responsibilities of a stable job, marriage and even
parenthood. Textbook general characteristics of emerging adults are: An age of identity exploration, an
age of instability or mobility, an age of self-focus, an age of feeling in between, and lastly an age of
possibilities. Overall emerging adults are those who are finding themselves and becoming settled into
who they are. Emerging adulthood is an important stage in life. It helps one understand their resilience,
because of the important changes in a functional capacity, educational achievement, and social roles.
These are large and very significant influences on one’s life course outcomes. According to Erikson’s
theory there are stages of Psychosocial Development emerging adults are experiencing.
Growing evidence suggests that an individual at the end of adolescence cannot be considered
to be an adult when using physical, physiological, intellectual, social, emotional, and behavioral
measures. When adolescents in developed societies mature and achieve adult body size, their
behavior often remains immature. Specialists in adolescent medicine have recognized this
incongruity, and have redefined adolescence to include young adults up to age 24 years, of
whom many have not yet assumed adult roles (1, 2). Reproduction in contemporary forager
societies also begins several years after adolescence and post-adolescent individuals are often
limited in their gathering and/or hunting skills (3–5). Compared to other mammals, primates
produce few offspring. Humans have an even slower growth rate than that of non-human
primates of comparable size, but human growth may be even more prolonged than is generally
realized.
Arnett proposed emerging adulthood as a phase of life between adolescence and full-fledged
adulthood, with distinctive demographic, social, and subjective psychological features (6, 7).
This life- history stage applies to individuals aged between 18 and 25 years, the period during
which they become more economically independent by training and/or education. Previously,
the psychodynamic theorist Erik Erikson identified a stage that he called a prolonged
adolescence or psychosocial moratorium in young people in developed societies (8, 9). Much
more recently, Hopwood and colleagues explored genetic and environmental influences on
personality development during the transition to adulthood in same-sex male and female
monozygotic and dizygotic twins assessed in late adolescence (approximately age 17 years),
emerging adulthood (~24 years), and young adulthood (~29 years) (10). Their genetically-
informed results support a life-course perspective on personality development during the
transition to adulthood. In addition, the United Nations has identified youth, defined as the
period from 15 to 24 years of age, as a period of vulnerability worldwide and has made it a
priority for multiple interventions (11).
Here, we use an evolutionary approach in order to understand emerging adulthood, arguing
that it is not just a sociological transition period but a biological life-history phase. Trait
variability, whether it is molecular, cellular, physiological, morphological, or behavioral, is the
leading edge of evolution. Together with genetic evolution, plasticity in developmental
programming has evolved to provide the organism with traits that can secure its survival and
reproductive success (12). Life-history theory is a powerful tool for understanding child growth
and development from an evolutionary perspective (2, 13, 14). We provide evidence that
emerging adulthood exists in some other mammals, which implies genetic evolution, and we
discuss emerging adulthood in foraging as well as developed societies, which implies the
occurrence of adaptive plasticity and cultural influences. We propose that genetic and cultural
evolution have interacted to produce the emerging adulthood stage in human life history.
the Transition from Adolescence to Emerging Adulthood
Determining the exact time of transitions between life-history stages is challenging (13).
Saltations (growth spurts) and transitions occur during human growth (15, 16), and stages have
a central place in evolutionary life-history theory, but the turning points are theoretical
constructions in which some aspects of a transition are highlighted.
Puberty produces an endocrine transformation with striking somatic and behavioral changes,
especially in body image, sex identity, aggression, and impulsivity. To define a maturational
stage between adolescence and adulthood, we need first to define the end of adolescence.
During this transition, growth velocity decelerates, blood and tissue hormone levels increase,
aggression becomes less overt, and learning and maturation mitigate hormonal impact.
Using maturational measures avoids the pitfalls of defining emerging adulthood according to
chronological age. For example, the Tanner scale of adolescent development is based on
external primary and secondary sex characteristics. Tanner stage V recognizes the conclusion of
puberty in boys when the testicular volume is >20 ml and the length of the penis is >14 cm (17)
and in girls when the breast reaches final adult size and the areola returns to the contour of the
surrounding breast with a projecting central papilla (18).
Here, we define the transition between adolescence and emerging adulthood as occurring
when growth returns to its prepubertal trajectory and the boy or girl is at Tanner stage IV (19).
Boys at this stage have a testicular volume between 12 and 20 ml, their scrotal skin darkens,
and the length of their penis is ~10 cm. Girls at this stage have experienced menarche, their
breasts are of adult size and elevated, and the areola and papilla form a secondary mound
which projects from the contour of the surrounding breast. Body composition continues to
change during emerging adulthood, in terms of relative fat mass, lean body mass, and total
body bone mineral content and bone mineral density increase (20), but the most important
maturational changes after adolescence, even if defined as the end of Tanner Stage 4, are in the
brain.
Brain size may be a pacemaker in mammalian life history (21), and it underlies the remarkable
human capacity for learning and communication, but the length of the brain's developmental
trajectory was until recently underestimated. It is now clear that brain development does not
stop with the completion of puberty when adult brain size is attained. Brain maturation
continues beyond adolescence, extending until around age 25 years, and this recently
discovered prolongation provides critical support for emerging adulthood as a post-adolescent
maturational stage (22). Compared to other primates, human newborns are neurologically and
behaviorally altricial because many aspects of brain development are protracted, including that
of the prefrontal cortex (23). The cortical architectural units or minicolumns in the prefrontal
cortex of humans are wider than those of the great apes, an increase that occurs after puberty
in humans, but not in chimpanzees (24). In chimpanzees, but not in humans, myelination
becomes complete at about the time of sexual maturity (25). Interestingly, human brain regions
with protracted development are the same that have undergone the greatest degree of
volumetric enlargement in primate evolution (26).
In a large-scale longitudinal pediatric neuroimaging study, brain maturation was found to
continue after adolescence: post-adolescent increases in white matter are linear while the
changes in the cortical gray matter are non-linear. Cortical white matter in particular continues
to increase into the mid-twenties, which is likely related to the efficiency and speed of cortical
connectivity (27, 28). In another study, Sowell and her colleagues spatially and temporally
mapped brain maturation in North American adolescents (age 12–16 years) and young adults
(age 23–30 years) using a whole-brain, voxel-by-voxel statistical analysis of high-resolution
structural magnetic resonance images (29). They found that the pattern of brain maturation
during these years was distinct from earlier development and was localized to large regions of
the dorsal, medial, and orbital frontal cortex and lenticular nuclei. They also reported relatively
little change at other brain locations. They concluded that cognitive function improves
throughout adolescence, and this improvement is associated with parallel post-adolescent
reductions in gray matter density (as white matter increases) in frontal and striatal regions. It
has been argued that such brain changes should mitigate the guilt of adolescent delinquents
who have not yet gone through them (30–32).
Asato and colleagues also investigated white matter maturation during adolescence using
diffusion tensor imaging and reported that (a) pubertal hormones influence white matter
development and maturation and (b) white matter connectivity and the executive control of
behavior is still immature in adolescence (33). Jolles and colleagues investigated the association
between whole-brain functional connectivity and cognitive and emotional functions in children
(11–13 years) and young adults (19–25 years) (34). Although they found similar patterns of
functional connectivity in children and young adults, there were differences in the size of the
functionally connected regions and the strength of functional connectivity. Thus, functional
connectivity continues to change during and after adolescence, and these developmental
differences in functional connectivity patterns were associated with higher cognitive or
emotional functions and basic visual and sensorimotor functions.
In another study comparing social and emotional functioning of children, adolescents, and
young adults, by analyzing the age-dependent development of five functionally distinct
cingulate-based intrinsic connectivity networks (ICNs), Kelly and colleagues provide additional
evidence that brain maturation extends beyond adolescence into young adulthood (35). They
found that the pattern of correlation with voxels proximal to the seed region of interest was
age-dependent: the pattern was diffuse in children (mean age 10.6 years), was less diffuse in
adolescents (mean age 15.4 years), and showed signs of becoming focal in young adults (mean
age 22.4 years). Also, the greatest development occurred in those ICNs associated with social
and emotional functions. Finally, in their study of the brains of 103 healthy subjects aged 5–32
years using diffusion tensor tractography, Lebel and Beaulieu provide further evidence that
brain maturation continues from childhood into adulthood (36). Association tracts show within-
subject maturation of measures indicative of myelination and axon density.
Collectively, these studies provide strong evidence that brain development and maturation
continue in young adulthood; the idea that brain maturation is finalized during adolescence is
no longer tenable. Psychologically, emerging adulthood is a stage when an individual's cognitive
abilities increase to reach their peak in their fourth decade and possibly beyond (37). Schaie
and colleagues included 13 measures of crystallized abilities influenced by schooling and
experience. The critical abilities from this perspective are those that enable the learning of new
things, that is, working memory and fluid intelligence; these, as well as processing speed (38),
peak in the mid 20s.
Emerging adulthood is also a social stage: it is a period of learning about intimacy and mutual
support, intensification of pre-existing friendships, family-oriented socialization, political
awareness, developing new relationships, and the attainment of biosocial skills that are needed
for successful mating and reproduction. Finally, it is also a stage of understanding self-concepts
and ideal concepts, emphasized interpersonal reactivity and obligation, self-expressiveness, and
contempt toward particular ideologies (39). The attainment of these cognitive, emotional, and
social abilities is the result of a complex interplay of maturation and interaction with the
environment, but it is now possible to say that at least in the earlier years of emerging
adulthood, they are correlated with and possibly caused by brain maturation. There is also
evidence that brain size growth continues into the third decade in some individuals. In these
individuals, hypothalamic maturation, puberty, and the resultant hormonal surges are
dissociated from and even precede development and maturity of frontal cortex (40, 41).
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