A large and relatively new body of research is revealing that young adulthood is a time of dramatic change in basic thinking structures, as well as in the brain. Consensus is emerging that an 18-year-old is not the same person she or he will be at 25, just as an 11-year-old is not the same as he or she will be at 18. They don't look the same, feel the same, think the same, or act the same.
The Mental Visor
Fundamentally, what changes in these developmental shifts is not just what people think, but also what they think about. Everyone, including young adults, has a kind of mental "visor" that screens out some kinds of phenomena while letting in others for consideration. As development unfolds, one can "see" and think about more and more complex phenomena such as abstractions, relationships, and moral problems, offering more and more powerful thinking tools.
Why does development happen? Most researchers see a role both for nature and nurture. In healthy people, some changes evolve on a biological timetable, as long as the environment is "good enough," and some changes are prompted by demands in the environment, as long as the biological underpinnings are "good enough."
When teens enter young adulthood, their thinking capacities, relationship skills, and ability to regulate emotions are unlikely to be at a developmental level where they can cope easily with the demands of a diverse, global, technological, rapidly-changing world. If all goes well, biology and environment bring a surge of growth paralleling those of childhood and adolescence.
An Emerging Field
Acknowledging these findings, researchers have begun to define young adulthood as its own developmental period, referring to it as "emerging adulthood," "the frontier of adulthood," or, earlier, "the novice phase." Here at the start of the 21st century, researchers are creating a new field around young adulthood, just as, at the turn of the 20th century, researchers defined a new field around adolescence.
Much of the impetus and focus for the research has come from the lengthening period in the U.S. between the onset of puberty and the fulfilling of cultural expectations around adult roles like financial independence and family formation. Significant differences can be expected across culture and circumstance.