Now it happens that some people are interested in the welfare and high development of the human race; but leaving aside those exceptional people, all fathers and mothers are interested in the welfare of their own families. The dearest thing to the parental heart is to have the children marry well and rear a noble family. How short-sighted it is then for such a family to take into its midst a child whose pedigree is absolutely unknown; or, where, if it were partially known, the probabilities are strong that it would show poor and diseased stock, and that if a marriage should take place between that individual and any member of the family the offspring would be degenerates.[39]

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.

The nobility of the Germanic, Celtic, and Slavic cultures that dominated Europe after the decline of the Roman Empire denounced the practice of adoption.[15] In medieval society, bloodlines were paramount; a ruling dynasty lacking a "natural-born" heir apparent was replaced, a stark contrast to Roman traditions. The evolution of European law reflects this aversion to adoption. English Common Law, for instance, did not permit adoption since it contradicted the customary rules of inheritance. In the same vein, France's Napoleonic Code made adoption difficult, requiring adopters to be over the age of 50, sterile, older than the adopted person by at least 15 years, and to have fostered the adoptee for at least six years.[16] Some adoptions continued to occur, however, but became informal, based on ad hoc contracts. For example, in the year 737, in a charter from the town of Lucca, three adoptees were made heirs to an estate. Like other contemporary arrangements, the agreement stressed the responsibility of the adopted rather than adopter, focusing on the fact that, under the contract, the adoptive father was meant to be cared for in his old age; an idea that is similar to the conceptions of adoption under Roman law.[17]
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]

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]

Europe's cultural makeover marked a period of significant innovation for adoption. Without support from the nobility, the practice gradually shifted toward abandoned children. Abandonment levels rose with the fall of the empire and many of the foundlings were left on the doorstep of the Church.[18] Initially, the clergy reacted by drafting rules to govern the exposing, selling, and rearing of abandoned children. The Church's innovation, however, was the practice of oblation, whereby children were dedicated to lay life within monastic institutions and reared within a monastery. This created the first system in European history in which abandoned children did not have legal, social, or moral disadvantages. As a result, many of Europe's abandoned and orphaned children became alumni of the Church, which in turn took the role of adopter. Oblation marks the beginning of a shift toward institutionalization, eventually bringing about the establishment of the foundling hospital and orphanage.[18]

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]