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]
Concerning developmental milestones, studies from the Colorado Adoption Project examined genetic influences on adoptee maturation, concluding that cognitive abilities of adoptees reflect those of their adoptive parents in early childhood but show little similarity by adolescence, resembling instead those of their biological parents and to the same extent as peers in non-adoptive families.[114]

By 1979, representatives of 32 organizations from 33 states, Canada and Mexico gathered in Washington, DC to establish the American Adoption Congress (AAC) passing a unanimous resolution: "Open Records complete with all identifying information for all members of the adoption triad, birthparents, adoptive parents and adoptee at the adoptee's age of majority (18 or 19, depending on state) or earlier if all members of the triad agree."[161] Later years saw the evolution of more militant organizations such as Bastard Nation (founded in 1996), groups that helped overturn sealed records in Alabama, Delaware, New Hampshire, Oregon, Tennessee, and Maine.[162][163] Simultaneously, groups such as Origins USA (founded in 1997) started to actively speak about family preservation and the rights of mothers.[164] The intellectual tone of these recent reform movements was influenced by the publishing of The Primal Wound by Nancy Verrier. "Primal wound" is described as the "devastation which the infant feels because of separation from its birth mother. It is the deep and consequential feeling of abandonment which the baby adoptee feels after the adoption and which may continue for the rest of his life."[153]
Adoptions can occur either between related family members, or unrelated individuals. Historically, most adoptions occurred within a family. The most recent data from the U.S. indicates about half of adoptions are currently between related individuals.[78] A common example of this is a "stepparent adoption", where the new partner of a parent may legally adopt a child from the parent's previous relationship. Intra-family adoption can also occur through surrender, as a result of parental death, or when the child cannot otherwise be cared for and a family member agrees to take over.
More recent research found that in a sample of mothers who had released their children for adoption four to 12 years prior, every participant had frequent thoughts of their lost child. For most, thoughts were both negative and positive in that they produced both feelings of sadness and joy. Those who experienced the greatest portion of positive thoughts were those who had open, rather than closed or time-limited mediated adoptions.[123]
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]
Adoption practices have changed significantly over the course of the 20th century, with each new movement labeled, in some way, as reform.[152] Beginning in the 1970s, efforts to improve adoption became associated with opening records and encouraging family preservation. These ideas arose from suggestions that the secrecy inherent in modern adoption may influence the process of forming an identity,[153][154] create confusion regarding genealogy,[155] and provide little in the way of medical history.

Although adoption is today practiced globally, the United States has the largest number of children adopted per 100 live births. The table below provides a snapshot of Western adoption rates. Adoption in the United States still occurs at nearly three times those of its peers although the number of children awaiting adoption has held steady in recent years, hovering between 133,000 and 129,000 during the period 2002 to 2006.[52]

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]
Infant adoption during Antiquity appears rare.[4][7] Abandoned children were often picked up for slavery[8] and composed a significant percentage of the Empire's slave supply.[9][10] Roman legal records indicate that foundlings were occasionally taken in by families and raised as a son or daughter. Although not normally adopted under Roman Law, the children, called alumni, were reared in an arrangement similar to guardianship, being considered the property of the father who abandoned them.[11]

Family preservation: As concerns over illegitimacy began to decline in the early 1970s, social-welfare agencies began to emphasize that, if possible, mothers and children should be kept together.[156] In the U.S., this was clearly illustrated by the shift in policy of the New York Foundling Home, an adoption-institution that is among the country's oldest and one that had pioneered sealed records. It established three new principles including "to prevent placements of children...," reflecting the belief that children would be better served by staying with their biological families, a striking shift in policy that remains in force today.[157]

In Spain under Francisco Franco’s 1939–75 dictatorship the newborns of some left-wing opponents of the regime, or unmarried or poor couples, were removed from their mothers and adopted. New mothers were frequently told their babies had died suddenly after birth and the hospital had taken care of their burials, when in fact they were given or sold to another family. It is believed that up to 300,000 babies were involved. These system – which allegedly involved doctors, nurses, nuns and priests – outlived Franco’s death in 1975 and carried on as an illegal baby trafficking network until 1987 when a new law regulating adoption was introduced.[180][181] 

Adoption practices have changed significantly over the course of the 20th century, with each new movement labeled, in some way, as reform.[152] Beginning in the 1970s, efforts to improve adoption became associated with opening records and encouraging family preservation. These ideas arose from suggestions that the secrecy inherent in modern adoption may influence the process of forming an identity,[153][154] create confusion regarding genealogy,[155] and provide little in the way of medical history.
The adoptee population does, however, seem to be more at risk for certain behavioral issues. Researchers from the University of Minnesota studied adolescents who had been adopted and found that adoptees were twice as likely as non-adopted people to suffer from oppositional defiant disorder and attention-deficit/hyperactivity disorder (with an 8% rate in the general population).[135] Suicide risks were also significantly greater than the general population. Swedish researchers found both international and domestic adoptees undertook suicide at much higher rates than non-adopted peers; with international adoptees and female international adoptees, in particular, at highest risk.[136]
^ Carlson, V., Cicchetti, D., Barnett, D., & Braunwald, K. (1995). Finding order in disorganization: Lessons from research on maltreated infants' attachments to their caregivers. In D. Cicchetti & V. Carlson (Eds), Child Maltreatment: Theory and research on the causes and consequences of child abuse and neglect (pp. 135–157). NY: Cambridge University Press.
Markedly different from the modern period, ancient adoption practices put emphasis on the political and economic interests of the adopter,[4] providing a legal tool that strengthened political ties between wealthy families and created male heirs to manage estates.[5][6] The use of adoption by the aristocracy is well documented; many of Rome's emperors were adopted sons.[6] Adrogation was a kind of Roman adoption which required the adrogator to be at least 60 years old.
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]
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]