proceedings. It is a legal avenue unique to adoptive parents as disruption/dissolution does not apply to biological kin, although biological family members are sometimes disowned or abandoned. Ad hoc studies performed in the U.S., however, suggest that between 10 and 25 percent of adoptions through the child welfare system (e.g., excluding babies adopted from other countries or step-parents adopting their stepchildren) disrupt before they are legally finalized and from 1 to 10 percent are dissolved after legal finalization. The wide range of values reflects the paucity of information on the subject and demographic factors such as age; it is known that teenagers are more prone to having their adoptions disrupted than young children. Adoption by same-sex couples Joint adoption by same-sex couples is legal in 34 countries as of March 2022, and additionally in various sub-national territories. Adoption may also be in the form of step-child adoption (6 additional countries), wherein one partner in a same-sex couple adopts the child of the other. Most countries that have same-sex marriage allow joint adoption by those couples, the exceptions being Ecuador (no adoption by same-sex couples), Taiwan (step-child adoption only) and Mexico (in one third of states with same-sex marriage). A few countries with civil unions or lesser marriage rights nonetheless allow step- or joint adoption. Parenting of adoptees Parenting 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 people are less interested in sustaining the genetic lines of others. This theory is supported in another more qualitative study wherein adoptive relationships marked by sameness in likes, personality, and appearance, were associated with both adult adoptees and adoptive parents report being happier with the adoption. 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