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]
The research says that the dysfunction, untruths and evasiveness that can be present in adoptive families not only makes identity formation impossible, but also directly works against it. What effect on identity formation is present if the adoptee knows they are adopted but has no information about their biological parents? Silverstein and Kaplan's research states that adoptees lacking medical, genetic, religious, and historical information are plagued by questions such as "Who am I?" "Why was I born?" "What is my purpose?" This lack of identity may lead adoptees, particularly in adolescent years, to seek out ways to belong in a more extreme fashion than many of their non-adopted peers. Adolescent adoptees are overrepresented among those who join sub-cultures, run away, become pregnant, or totally reject their families.[133][134]

Similar mechanisms appear to be at work in the physical development of adoptees. Danish and American researchers conducting studies on the genetic contribution to body mass index found correlations between an adoptee's weight class and his biological parents' BMI while finding no relationship with the adoptive family environment. Moreover, about one-half of inter-individual differences were due to individual non-shared influences.[115][116]
Bloodhounds are champion sniffers, but how do all of those flopping folds and jiggling jowls function? Meet the dogs who smell with their ears! Bloodhounds are champion sniffers — even by dog standards. Although every dog is certainly greater than the sum of its parts, there is some truth to the affectionate description of Bloodhounds as “noses with dogs attached.” …
During the same period, the Progressive movement swept the United States with a critical goal of ending the prevailing orphanage system. The culmination of such efforts came with the First White House Conference on the Care of Dependent Children called by President Theodore Roosevelt in 1909,[33] where it was declared that the nuclear family represented "the highest and finest product of civilization" and was best able to serve as primary caretaker for the abandoned and orphaned.[34][35] Anti-institutional forces gathered momentum. As late as 1923, only two percent of children without parental care were in adoptive homes, with the balance in foster arrangements and orphanages. Less than forty years later, nearly one-third were in an adoptive home.[36]
The number of adoptions in the United States peaked in 1970.[45] It is uncertain what caused the subsequent decline. Likely contributing factors in the 1960s and 1970s include a decline in the fertility rate, associated with the introduction of the pill, the completion of legalization of artificial birth control methods, the introduction of federal funding to make family planning services available to the young and low income, and the legalization of abortion. In addition, the years of the late 1960s and early 1970s saw a dramatic change in society's view of illegitimacy and in the legal rights[46] of those born outside of wedlock. In response, family preservation efforts grew[47] so that few children born out of wedlock today are adopted. Ironically, adoption is far more visible and discussed in society today, yet it is less common.[48]
Several factors affect the decision to release or raise the child. White adolescents tend to give up their babies to non-relatives, whereas black adolescents are more likely to receive support from their own community in raising the child and also in the form of informal adoption by relatives.[118] Studies by Leynes and by Festinger and Young, Berkman, and Rehr found that for pregnant adolescents, the decision to release the child for adoption depended on the attitude toward adoption held by the adolescent's mother.[119] Another study found that pregnant adolescents whose mothers had a higher level of education were more likely to release their babies for adoption. Research suggests that women who choose to release their babies for adoption are more likely to be younger, enrolled in school, and have lived in a two-parent household at age 10, than those who kept and raised their babies.[120]
Taken together, these trends resulted in a new American model for adoption. Following its Roman predecessor, Americans severed the rights of the original parents while making adopters the new parents in the eyes of the law. Two innovations were added: 1) adoption was meant to ensure the "best interests of the child;" the seeds of this idea can be traced to the first American adoption law in Massachusetts,[16][23] and 2) adoption became infused with secrecy, eventually resulting in the sealing of adoption and original birth records by 1945. The origin of the move toward secrecy began with Charles Loring Brace who introduced it to prevent children from the Orphan Trains from returning to or being reclaimed by their parents. Brace feared the impact of the parents' poverty, in general, and their Catholic religion, in particular, on the youth. This tradition of secrecy was carried on by the later Progressive reformers when drafting of American laws.[44]

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]