I will rely on a fair amount of data to discuss what I see as the significance of international adoption. However, I want to begin with a single number that will put the rest of this essay in context: the World Health Organization reports that more than ten million children under five years old – most of them in developing countries – die each year from violence, malnutrition or disease.

Ten million is hard to comprehend. Nor is it any easier if we break it down: thirty thousand children each day; more than one thousand every hour. Every day, the toll of children's lives equals ten times the number who died in the World Trade Towers, and each week matches the total of fatalities in the 2004 Asian tsunami. Deaths equaling fifty tsunamis each year – a number that has not budged much in a decade, by the way – but sadly, to quote an op-ed piece published years ago by A. M. Rosenthal of the Times, it is not news.

In the long run, all international humanitarian intervention – medical assistance, constitution-making, adoption and in-country development – is propelled by that number ten million, by the desire to help some of those children find the stability and the health and the homes that will enable them to survive, and perhaps even to flourish. The fact that many of those efforts fail does not subtract from the need to remain engaged.

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Adoption is among the oldest and most widespread of human social practices. The Code of Hammurabi, promulgated in the 18th century BCE, includes a definition of adoption. Scores of other literary and historical texts document that, in one form or another, for a variety of motives, and with an equally diverse set of outcomes, orphaned and abandoned children have circulated among families throughout human history.

Children have been adopted, legally and extra-legally, formally and informally, to constitute or re-constitute families, to provide homes when birth parents could not or would not do so, to serve as slaves, on the one hand, or to replace disinherited or deceased heirs on the other.

In his path breaking book, The Kindness of Strangers, John Boswell uncovered a previously hidden history, tracking the lives of children abandoned in Europe from the late classical through the early modern periods. Boswell concluded that children were abandoned in large numbers, but rarely with the intention of infanticide. Instead, many societies developed protocols – rarely written down but universally understood – for the orderly circulation of children: from families who, for whatever reason, chose or needed to give up a child to families who, again for all the reasons mentioned above, wanted to add a child. Boswell's data (incomplete, to be sure) suggest that mortality rates for abandoned children were probably about the same as for children who remained in intact families.

The European story continued in the New World. While adoption in Colonial America can be traced back to the early years of white settlement, the practice was long governed informally and on an ad hoc basis. Relatives, sometimes neighbors without legal authorization, took in abandoned children or those who lost their parents. In the 18th and 19th centuries, less fortunate children could find themselves marooned in "poor houses" or orphanages, often until their 16th birthdays. In 1851, Massachusetts enacted the first modern adoption law, which recognized adoption as a social and legal matter requiring state supervision.

If 1851 was late in the history of adoption, it was actually early in the history of adoption law. The United Kingdom, for example, did not enact legislation regulating adoption until 1926. Some historians of adoption have argued that the practice may have seemed more compatible with American cultural assumptions than with those of other countries. Families created by choice rather than biology, that is to say, enact a process that perhaps rhymes with our democratic professions.

The total number of annual adoptions finalized in the U.S. rose through the first seven decades of the twentieth century, reaching a high point of 175,000 in 1970. Since then, the number of adoptions has declined, to about 120,000 each year, and so too has the ratio of what are called "stranger" adoptions, i.e., adoptions between unrelated persons, a category that includes inter-country adoptions. Reflecting changes in marriage, cohabitation, and divorce rates, the majority of domestic adoptions now involve persons with some previous relation; in particular the adoption of stepchildren is now much more common.

The category of adopted children and stepchildren was included for the first time in the 2000 census. The census determined the total children of householders to be 84 million, of whom two million – just over two percent – were adopted.

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Aside from its precedence, the 1851 Massachusetts law represented an important development because it grounded the legitimacy of adoption on the welfare of the child. Judges insisted that prospective parents should be "fit and proper." For a century-and-a-half, that view of adoption has guided state, federal and indeed international law. The prevailing legal norm is called "the best interest of the child" doctrine, and it provides the standard that must be satisfied in every adoption, whether domestic or international. Article 1A of the 1995 Hague Convention, which governs inter-country adoption, states that the Convention's primary object is to "establish safeguards to ensure that inter-country adoptions take place in the best interests of the child…."

Needless to say, the interpretation of that dictum has led to wide variations in judgment, in the cases of both domestic and international adoptions. How to measure the "best interests" of a child, and who would do the measuring? For many years, and until quite recently, a blinkered notion of "matching" guided private and public agencies in the management of adoption.

Resisting precisely the difference on which adoptive families are based, social workers insisted on placing children with families whom they most closely resembled: not merely in physical appearance – blue eyes with blue eyes, if possible, certainly white with white – but also in such invisible markers as religion. Certain countries still adhere to versions of these strictures: Colombia, for example, grants preference to prospective parents of Colombian descent; the Philippines requires prospective parents to demonstrate membership in some religious organization.

The implications for inter-ethnic and international adoption are obvious: since such adoptions frequently made matching impossible, they were discouraged, and in some quarters still are – a topic to which I shall return.

Social workers also created a category for children they did not hesitate to call "unadoptable": children of color and foreign children, handicapped and older children, children in sibling groups. It took a generation of leadership, usually exhibited by people outside the professional social work community, among them the novelist-activist Pearl S. Buck, to reform those pernicious notions.

While domestic adoptions have declined, international adoptions have increased, though the numbers remain small. In the year 2000, 18,000 immigrant visas for adoption were issued, up from 7,000 in 1990. According once again to the 2000 census, the total population of children adopted internationally is 260,000, somewhat fewer than one out of every three hundred children.

Despite the relatively small scale of international adoption, both within the U.S. and within other receiving (mostly European) countries, it clearly represents the most notable shift in adoption practices of the past fifty or so years. International and interracial adoptive families, as one source puts it, have "literally made adoption more visible than it was in the past."

World War II marked the effective beginnings of international adoption, at least in the United States. From 1935 to 1948, an average of only 14 children a year, "under 16 years of age, unaccompanied by parent," entered the country. In short, international adoption has emerged at the intersection of twentieth-century crises, especially warfare, changing notions of humanitarian intervention, and technologies that have enabled the movement of abandoned children across national boundaries.