Other studies provide evidence that adoptive relationships can form along other lines. A study evaluating the level of parental investment indicates strength in adoptive families, suggesting that parents who adopt invest more time in their children than other parents and concludes, "...adoptive parents enrich their children's lives to compensate for the lack of biological ties and the extra challenges of adoption."[94] Another recent study found that adoptive families invested more heavily in their adopted children, for example, by providing further education and financial support. Noting that adoptees seemed to be more likely to experience problems such as drug addiction, the study speculated that adoptive parents might invest more in adoptees not because they favor them, but because they are more likely than genetic children to need the help.[95]
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]
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]

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]
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]
The research literature states adoptees give four reasons for desiring reunion: 1) they wish for a more complete genealogy, 2) they are curious about events leading to their conception, birth, and relinquishment, 3) they hope to pass on information to their children, and 4) they have a need for a detailed biological background, including medical information. It is speculated by adoption researchers, however, that the reasons given are incomplete: although such information could be communicated by a third-party, interviews with adoptees, who sought reunion, found they expressed a need to actually meet biological relations.[167]
Nevertheless, work on adult adoptees has found that the additional risks faced by adoptees are largely confined to adolescence. Young adult adoptees were shown to be alike with adults from biological families and scored better than adults raised in alternative family types including single parent and step-families.[137] Moreover, while adult adoptees showed more variability than their non-adopted peers on a range of psychosocial measures, adult adoptees exhibited more similarities than differences with adults who had not been adopted.[138] There have been many cases of remediation or the reversibility of early trauma. For example, in one of the earliest studies conducted, Professor Goldfarb in England concluded that some children adjust well socially and emotionally despite their negative experiences of institutional deprivation in early childhood.[139] Other researchers also found that prolonged institutionalization does not necessarily lead to emotional problems or character defects in all children. This suggests that there will always be some children who fare well, who are resilient, regardless of their experiences in early childhood.[140] Furthermore, much of the research on psychological outcomes for adoptees draws from clinical populations. This suggests that conclusions such that adoptees are more likely to have behavioral problems such as ODD and ADHD may be biased. Since the proportion of adoptees that seek mental health treatment is small, psychological outcomes for adoptees compared to those for the general population are more similar than some researchers propose.[141]
These practices have become significant social and political issues in recent years, and in many cases the policies have changed.[176][177] The United States, for example, now has the 1978 Indian Child Welfare Act, which allows the tribe and family of a Native American child to be involved in adoption decisions, with preference being given to adoption within the child's tribe.[178]
Foster care adoption: this is a type of domestic adoption where a child is initially placed in public care. Many times the foster parents take on the adoption when the children become legally free. Its importance as an avenue for adoption varies by country. Of the 127,500 adoptions in the U.S. in 2000[83] about 51,000 or 40% were through the foster care system.[84]
Unlike guardianship or other systems designed for the care of the young, adoption is intended to effect a permanent change in status and as such requires societal recognition, either through legal or religious sanction. Historically, some societies have enacted specific laws governing adoption; where others have tried to achieve adoption through less formal means, notably via contracts that specified inheritance rights and parental responsibilities without an accompanying transfer of filiation. Modern systems of adoption, arising in the 20th century, tend to be governed by comprehensive statutes and regulations.