To prove individual identity or genetic relationships.
Back in 1985, the first genetic "fingerprint" was a miracle of science. Today, DNA analysis is standard practice for defining paternity or maternity, predisposition to disease, embryonic health, criminal guilt or innocence, and so on.
But in our context, DNA analysis is mainly used for genealogical and biohistorical investigations.
Traditional genealogy follows a chain of genetic links from generation to generation. If a link is erased, DNA testing can sometimes restore the bond.
For example, between 1976 and 1983, Argentina's ruling junta 'disappeared' 20,000 people - including 270 women who gave birth before dying. Desperate to find lost grandchildren, the mothers of the disappeared appealed to scientists, asking for a genetic test that didn't need parental DNA. As of May 2003, the grandmothers' DNA project has found 74 of the disappeared children (now in their late 20s).
In rare instances, the ends (decisive historical facts) can justify the means (exhumations and destructive sampling).
A case in point, the Romanovs' story began July 17, 1918, with the mass murder of Czar Nicholas II, his wife, and at least three of their five children. Their remains lay in a shallow grave, until discovered in 1979 by an amateur historian. He kept the secret for 10 more years. The remains were finally exhumed in 1991. After 7 years of forensic testing, investigators had enough DNA evidence to be almost certain it was the Czar's family. Exactly 80 years after their death, the Romanovs' remains were laid to rest.