The Riegel Y-DNA project has tested about a dozen men with surname Riegel or various spelling variations in an attempt to learn whether they descend from a common ancestor. The test results show that there are a number of unrelated families using the surname Reigel, Riegel, Riegle, Riggle, and the like, confirming the results of conventional genealogical research.

Our earliest known ancestor, Jacob K. Riegel, has been expected to have descended from Matheis Riegel (1610-1672) like many of the other families using that surname in early Pennsylvania. Three test subjects, who according to conventional genealogical research are descended from Matheis, do have identical results and thus would appear to display the pattern of his descendants. Tests of the descendants of Jacob K. all match each other, but do not match those of the three documented descendants of Matheis. Further, they do not match those of any other Riegel descendant who has been tested by the project.

Thus it would appear that the descendants of Jacob K. are not related to any other known Riegel family. While it is possible that a totally separate family using the surname Riegel immigrated to the United States, it seems more likely that there was a "non-paternity event," such as an unrecorded adoption. It was not uncommon in early America for a child to be taken in without formal proceedings after something happened to his parents. In some cases the child took on the surname of host family and knowledge of the "adoption" was lost after a generation or two.

There is some support for the theory that a "non-paternity event" may have been involved. The closest match to the test results of the Jacob K. descendants is a descendant of the Kraus family from Becherbach, a town in present-day Germany, the same region where Matheis lived. The match is far from exact, but does suggest a possible connection.

The recommended procedure in such cases is to test successively more distant cousins, thus testing with successively earlier common ancestors, to try to identify in which generation the "non-paternity event" occurred. This approach has proved difficult in this case, as displayed by the chart below. Y-DNA, which is passed virtually unchanged for many generations, is passed only from father to son. Jacob K. had only three sons, and only one of them has known living male-line descendants, Benjamin Franklin. So testing can only show that his sons all had the same father, and cannot determine whether he and his siblings had the same father.