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By the time an individual reaches early adulthood, many developmental milestones have already been attained. Logic, reasoning, autonomy, identity and physical growth normally are in place. However, as we enter into young adulthood, the highly self oriented development of our past years begins to minimize. A new focus begins to develop, namely an interest in losing one's own egocentrism and devoting oneself to another.
Erikson called this stage Intimacy vs. Isolation which results, if the stage is successfully passed, in the virtue of truly loving others.
This is a very challenging time period for the young adult, and unlike earlier stages which can be resolved often in five years or less, this stage may last fifteen years or more. Researchers like Zick Rubin discuss in greater detail the challenges of this time frame on young adults. Rubin and others stated that the process of developing intimate relationships is so complicated that establishing one successful relationship at an intimate level takes a minimum of a year and a half and that this process cannot be accelerated. Maslow also states that young adults not only struggle with love and belonging needs as mentioned, but are also trying to establish themselves vocationally attempting to reach the beginnings of prestige and esteem. Donald Super, a vocational theorist, saw young adulthood as a developmental struggle where the primary needs vary between the Implementation stage, ages 21-24 and the Stabilization stage, ages 24-35. Basically what he is saying is that young adulthood is a struggle to maintain an identity but in the social vocational world.
In mid life, although esteem needs are still pursued and vocational development is still seen, a shift in the nature of development occurs yet again. Researchers like Robert Peck, who built his theory on the principles of Erik Erikson, stated that mid life adults not only, as Erikson stated, struggle with passing on their life's work to younger generations but also struggle to appreciate their intellect vs their physical abilities. Men especially convert their interest in women from physical intimacy to pure friendship. Generally, a decline in physical ability demands that mid life adults adjust to the fact that they are now the dominate generation and are beginning to view the decline of their own lives.
It is important to know that not all theorists agree about mid life development. Erik Erikson received much criticism of his theory in this stage of development because develop of his theory was based on the need to have children to deal with the last stages of life and carry on one's legacy.
I hope this has helped you,