What is race? Is it a matter of biology or performance? Ancestry or appearance? Is it assigned by common sense or expertise? What happens, and why, if racial boundaries are uncertain? In Professor Ariela Gross's wonderful new book, What blood won't tell: a history of race on trial in America, she illuminates these questions by examining the disputes emerging on the borderlines of racial categories drawn by the law. In so doing, Gross tells the fascinating history of this important subject, and exposes uncomfortable similarities between modern racial practices and those of the past.

What blood won't tell breaks new ground in bringing together careful histories of many disparate sites of racial contestation in US law. The first third of the book largely concerns trials over the racial identity of those charged with African descent, in claims to freedom and litigation over inheritance, marriage, and libel. Later chapters, however, reach much more widely. They examine the Melungeons, Lumbees, and Narragansetts, all groups with distinct identities alleged to bring together multiple racial backgrounds; black ‘freedmen’ citizens of the Choctaw, Chickasaw, Seminole, Creek, and Cherokee tribes seeking recognition within those tribal groups; Native Hawaiian debates over blood quantum in the effort to secure justice after the illegal annexation of the Kingdom of Hawai'i; Asian and Middle Eastern immigrants arguing that they were white for purposes of federal restrictions on naturalization; Filipinos charged with miscegenation for marrying whites; and Mexicans debating over whether to claim whiteness in their struggles for civil rights. Although this might seem beyond the ability of any single historian to cover well, Gross has undertaken thorough archival research and provides new facts and insights even for those already very familiar with each subject.

By combining these varied areas, Gross shows the ways they are linked as well. All of these legal debates involved some measure of ‘science’ and arguments from biological descent. They include, for example, claims that a person of African descent could be known by the arches of her feet; decisions that the Chinese were really the ancestors of the indigenous Americans and therefore were included in a California law that barred Indian testimony; and debates over whether people of mixed race were biological mules, mongrels sapped of the strength of both races, or whether they took advantage of the supposed qualities of both races.

But Gross importantly shows that individual performances of race and community understandings of racial identity were at least as important, and even won the day over biological descent and science, in most of the contexts she discusses. Thus testimony that a woman embodied purity and modesty, that a man voted, mustered for war, or did jury duty, and that either was accepted into the homes and at the social engagements of the white community was decisive in juror ascriptions of race in trials over blackness. For South Asians or ‘Hindus’ their scientific classification as Caucasian or Aryan had to yield in the face of the ‘good sense and common understanding of ordinary men’ (p. 243, quoting a brief of the United States in United States v. Thind, 261 U.S. 204 (1923)). In a different context, legal classification of Mexicans as white faltered under popular insistence on racial difference, as Mexicans were excluded from juries and white schools, based on untested allegations of lack of English skills and citizenship. In the face of uncertain racial categories, in other words, jurors, legislators, and administrative agencies repeatedly decided in favour of community power to recognize who was appropriately inside and who was outside the favoured group.

In her conclusion, Gross ties the insights of the book to the present day. If decisions about race, she argues, were less about colour and biology than about performance and association – about who, in other words, the dominant community permitted to form part of the governing caste – then simply prohibiting legal consideration of colour or biology cannot undo the role race plays in contemporary social and economic ordering. Even if one disagrees with the contemporary implications of her research, there can be no disagreement about her achievement. This is an engaging and illuminating book and a substantial contribution. It must be read by all those interested in race in America, and should be read by all who want a fascinating new perspective on American law and history.