In my DNA presentation on Saturday I used this quote from Helen. It says that without DNA testing there’s no way to establish a relationship beyond a reasonable doubt. Helen used DNA results, along with other evidence in arguing why President Thomas Jefferson was almost certainly the father of his slave Sally Hemming's children.
If your genealogy relies solely on paper records it may, or at least before the days of DNA evidence may have met the Genealogical Proof Standard (GPS), but not the standard of beyond a reasonable doubt. Clearly Leary regards DNA to be the type of high quality source that the GPS requires be examined.
When Helen Leary wrote in 1998 she had to add that such DNA tests were not practical. 15 years later that’s no longer the case.
Today, if DNA information can help, and you’re not using it, there’s no way you can meet the Genealogical Proof Standard. Like Helen all professional genealogists who profess to adhere to the GPS should keep up to date on genetic genealogy, a rapidly developing field. Analysis techniques are being developed so that one day, perhaps not so far in the future, we may be able to match segments of autosomal DNA providing evidence of lineage as strong or stronger than provided by conventional paper genealogical sources alone.