Field
The disclosed embodiments relate to discovering historical populations from the pattern of genetic relationships between people. 
Description of Related Art
Although humans are, genetically speaking, almost entirely identical, small differences in human DNA are responsible for some observed variation between individuals.  In fact, by comparing these small differences in DNA of individuals, it is possible to detect long chromosome segments suggestive of inheritance from a recent common ancestor, and then use these detected segments to estimate how closely two people are related.  The process of identifying segments suggestive of recent common inheritance is known in population genetics literature as an analysis of identity-by-descent (IBD).  IBD analysis can be used to predict the familial relationship between any two people (e.g., second cousins) in a population as long as the relationship is due to shared common ancestors from the recent past. 
Learning about population structure from genetic polymorphism data is an important topic in genetics.  The most widely used methods in this area are based on modeling variation in allele frequencies.  These methods have shed light, for example, on historical patterns of migration in human populations.  To take one example of this, prior genetic studies of the United States (US) have helped to elucidate the diversity of recent immigrants in relation to other parts of the world (e.g. Europe, Africa).  By contrast, patterns of IBD can be used to study more recent demography of known populations, such as demographic events that have occurred within the US in the period beginning with European colonization. 
While researchers have previously used analysis of IBD patterns to learn about the history of different groups of people, using IBD to discover groups within hetereogeneous populations such as the present-day US has not been done previously.