DoRIS is a tool for reconstructing fine-scale demographic events that occurred in the very recent past (e.g. ~100 generations) of one or multiple populations.
Two randomly chosen individuals from the same population may share genetic relatives in the recent past. The average number of recent ancestors shared at a given point in time is inversely proportional to how large the population is: pairs of individuals from small population are more likely to be distant cousins than individuals from large populations. Similarly, two individuals from distinct groups that admixed very recently may share a number of common ancestors, depending on the rate at which their ancestors migrated across populations.
Although we cannot directly observe the presence of past genetic ancestors, these hidden relationships often result in long genomic regions that are identical-by-descent (IBD) in groups of distant relatives, who are typically unaware of their relatedness. DoRIS infers the parameters of several possible demographic models using the density of IBD segments of different lengths.
This type of analysis can reveal subtle population size fluctuations in the recent past (e.g. bottlenecks in the past 100 generations, see this paper), and relationships across groups within small geographic regions (e.g. within a country, see this paper).