Previous research on adoption has led to assumptions that indicate that there is a heightened risk in terms of psychological development and social relationships for adoptees. Yet, such assumptions have been clarified as flawed due to methodological failures. But more recent studies have been supportive in indicating more accurate information and results about the similarities, differences and overall lifestyles of adoptees.[125]
Common law adoption: this is an adoption which has not been recognized beforehand by the courts, but where a parent, without resorting to any formal legal process, leaves his or her children with a friend or relative for an extended period of time.[88][89] At the end of a designated term of (voluntary) co-habitation, as witnessed by the public, the adoption is then considered binding, in some courts of law, even though not initially sanctioned by the court. The particular terms of a common-law adoption are defined by each legal jurisdiction. For example, the US state of California recognizes common law relationships after co-habitation of 2 years. The practice is called "private fostering" in Britain.[90]
There is limited research on the consequences of adoption for the original parents, and the findings have been mixed. One study found that those who released their babies for adoption were less comfortable with their decision than those who kept their babies. However, levels of comfort over both groups were high, and those who released their child were similar to those who kept their child in ratings of life satisfaction, relationship satisfaction, and positive future outlook for schooling, employment, finances, and marriage.[121] Subsequent research found that adolescent mothers who chose to release their babies for adoption were more likely to experience feelings of sorrow and regret over their decision than those who kept their babies. However, these feelings decreased significantly from one year after birth to the end of the second year.[122]
The biological relationship between a parent and child is important, and the separation of the two has led to concerns about adoption. The traditional view of adoptive parenting received empirical support from a Princeton University study of 6,000 adoptive, step, and foster families in the United States and South Africa from 1968 to 1985; the study indicated that food expenditures in households with mothers of non-biological children (when controlled for income, household size, hours worked, age, etc.) were significantly less for adoptees; step-children, and foster children, causing the researchers to speculate that, instinctively, people are less interested in sustaining the genetic lines of others.[92] This theory is supported in another more qualitative study where in adoptive relationships marked by sameness in likes, personality, and appearance, both adult adoptees and adoptive parents report being happier with the adoption.[93]
Externally focused theories, in contrast, suggest that reunion is a way for adoptees to overcome social stigma. First proposed by Goffman, the theory has four parts: 1) adoptees perceive the absence of biological ties as distinguishing their adoptive family from others, 2) this understanding is strengthened by experiences where non-adoptees suggest adoptive ties are weaker than blood ties, 3) together, these factors engender, in some adoptees, a sense of social exclusion, and 4) these adoptees react by searching for a blood tie that reinforces their membership in the community. The externally focused rationale for reunion suggests adoptees may be well adjusted and happy within their adoptive families, but will search as an attempt to resolve experiences of social stigma.[167] 
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