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]

Identity is defined both by what one is and what one is not. Adoptees born into one family lose an identity and then borrow one from the adopting family. The formation of identity is a complicated process and there are many factors that affect its outcome. From a perspective of looking at issues in adoption circumstances, the people involved and affected by adoption (the biological parent, the adoptive parent and the adoptee) can be known as the "triad members and state". Adoption may threaten triad members' sense of identity. Triad members often express feelings related to confused identity and identity crises because of differences between the triad relationships. Adoption, for some, precludes a complete or integrated sense of self. Triad members may experience themselves as incomplete, deficient, or unfinished. They state that they lack feelings of well-being, integration, or solidity associated with a fully developed identity.[129]


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]
Social workers and other professionals in the field of adoption began changing terms of use to reflect what was being expressed by the parties involved. In 1979, Marietta Spencer wrote "The Terminology of Adoption" for The Child Welfare League of America (CWLA),[184] which was the basis for her later work "Constructive Adoption Terminology".[185] This influenced Pat Johnston's "Positive Adoption Language" (PAL) and "Respectful Adoption Language" (RAL).[186] The terms contained in "Positive Adoption Language" include the terms "birth mother" (to replace the terms "natural mother" and "real mother"), and "placing" (to replace the term "surrender"). These kinds of recommendations encouraged people to be more aware of their use of adoption terminology.

United States approx 136,000 (2008)[69] 3,978,500 (2015)[70] ≈3 per 100 live births The number of adoptions is reported to be constant since 1987. Since 2000, adoption by type has generally been approximately 15% international adoptions, 40% from government agencies responsible for child welfare, and 45% other, such as voluntary adoptions through private adoption agencies or by stepparents and other family members.[69]
The stigmas associated with adoption are amplified for children in foster care.[149] Negative perceptions result in the belief that such children are so troubled it would be impossible to adopt them and create "normal" families.[150] A 2004 report from the Pew Commission on Children in Foster Care has shown that the number of children waiting in foster care doubled since the 1980s and now remains steady at about a half-million a year."[151]
In the 1970s, as adoption search and support organizations developed, there were challenges to the language in common use at the time. As books like Adoption Triangle by Sorosky, Pannor and Baran were published, and support groups formed like CUB (Concerned United Birthparents), a major shift from "natural parent" to "birthparent"[182][183] occurred. Along with the change in times and social attitudes came additional examination of the language used in adoption.
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]
Identity is defined both by what one is and what one is not. Adoptees born into one family lose an identity and then borrow one from the adopting family. The formation of identity is a complicated process and there are many factors that affect its outcome. From a perspective of looking at issues in adoption circumstances, the people involved and affected by adoption (the biological parent, the adoptive parent and the adoptee) can be known as the "triad members and state". Adoption may threaten triad members' sense of identity. Triad members often express feelings related to confused identity and identity crises because of differences between the triad relationships. Adoption, for some, precludes a complete or integrated sense of self. Triad members may experience themselves as incomplete, deficient, or unfinished. They state that they lack feelings of well-being, integration, or solidity associated with a fully developed identity.[129]
Psychologists' findings regarding the importance of early mother-infant bonding created some concern about whether parents who adopt older infants or toddlers after birth have missed some crucial period for the child's development. However, research on The Mental and Social Life of Babies suggested that the "parent-infant system," rather than a bond between biologically related individuals, is an evolved fit between innate behavior patterns of all human infants and equally evolved responses of human adults to those infant behaviors. Thus nature "ensures some initial flexibility with respect to the particular adults who take on the parental role."[96]
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