Why are adoptees treated differently from biological children in numbering a genealogy? It’s a great question and deserves a reasoned answer. The response relies on background information in Numbering Your Genealogy.
A genealogy describes a family as it descends from a progenitor. In its simplest form it includes the genetic descendants of that person, what is sometimes referred to as the “bloodline.” It becomes more complex as the family grows to include stepchildren and adopted children. Some carry the DNA of the progenitor. Some do not. Some carry the same surname. Some do not. All, however, belong in the family, and we want to include them.
Adoptees are in a unique position, as they belong in two groups of genealogies. One group represents all the lines of their social (adoptive) family. The other group comprises the lines of their genetic family. How adoptees are described in the numbering scheme depends on which genealogy is in use. In a social genealogy, their generation number (1) indicates that they are the progenitor of a new genetic line within this family. In a genetic genealogy they take the appropriate generation number from the progenitor. Both assignments are accurate for the person, depending on which family the genealogy represents.
A good genealogical numbering system accommodates both genetic and social members of a family. With the popularity of direct-to-consumer genetic testing, genealogists are becoming more and more aware of the need to include all family members in genealogies. We want to use a numbering system that is flexible enough to describe everyone’s relationship to the progenitor accurately.
The examples used for this series of posts are drawn from a real genealogy that includes the genetic and social descendants of William Walker. All the “fathers unknown” are truly unknown. If someday their identities are discovered, the adoptive children in this Walker genealogy could also be numbered in the genetic genealogies of their paternal lines.
The adoptees in this Walker family all have a genetic relationship to one member of a Walker couple. The numbering principles used to describe them are equally appropriate for adoptees who have no genetic relationship to either member of a couple. The overarching goal is to include adoptees and stepchildren in a genealogy, acknowledging them both as part of the family and as having their own, new DNA signature in the family. Numbering Your Genealogy, which underpins this series of SpringBoard posts, gives us the tools to do just that.
 Madilyn Coen Crane, “Complex Families,” in Joan Ferris Curran, Madilyn Coen Crane, and John H. Wray, Numbering Your Genealogy: Basic Systems, Complex Families, and International Kin, ed. Elizabeth Shown Mills, rev. ed. (Arlington, Va.: National Genealogical Society, 2008), 17–25.