Ancestor
An Ancestor is any parent of one of your parents, or basically any ancestor of one of your parents. Purposely specified recursively. Your parents are also your ancestors. But convention has it that parents and grandparents are "too close" to be called ancestors. You are always descended from your ancestors. This strict definition can be more strictly defined as parent ancestors. A pedigree is a person's parent ancestors; often detailed in a chart, graph or table form.Some restrict the definition to blood lines or biological parents only; which is an important distinction for genetic genealogy and the inheritance of DNA. Others include adoption and similar legal, religious and cultural forms that create descendants from people.
Some widen to include other members of nuclear families at each generation. So Aunts and Uncles, for example. Especially if they share a common ancestor and thus the DNA of other, more strictly defined parent ancestors.
The first (or closest in relation) common ancestor is termed the Most Recent Common Ancestor (or MRCA). If full siblings, both your parents are the MRCA. And ditto for any descendants of those full siblings. (Unless you start to see some intermixing of the family lines.)
The "farthest back in time" known ancestor is termed the Earliest Known Ancestor (or EKA). "Known" means someone you can name and identify; often with some BMD details.
Sometimes a Defining Ancestor is used instead of an EKA to name a Family Branch. This because they are an intermediate ancestor between the EKA and the MRCA that is more famously known or recognized. Maybe an immigrant. Or earlier researched and understood ancestor. In these cases, the EKA will be described separately in the family branch identified by the Defining Ancestor. This can cause problems later on if you finddescendants of the EKA that are not descendants of the Defining Ancestor.
Special numbering schemes, like Ahnentafel number, have been developed to accurately identify any parent ancestor and how they are related to the descendant. We use Ahnentafel numbers in our match codes defined in this project. NEHGS developed their own to use in their publications.
Descendant
A Descendant is any child of one of your children, or basically any descendant of one of your children. Purposely specified recursively. Your children are also your descendants.Some may expand this to include non-biological children (such as through adoption) and "in-laws" (spouses of your more traditional descendants). Giving rise to a distinction of a biological descendant tree and a genealogical one.
If you have a common ancestor with someone, then you are both descendants of that common ancestor.
Genealogy professionals have developed naming schemes to accurately name any descendant when the order and number of children born are known for each generation; down to the final or target descendant. See the references for some of these defined standards for descendants. Some are more robust and do not require full knowledge of all the descendants before hand.
External References
- Genealogical Numbering Systems on Wikipedia