Lineage

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A headmate's lineage or split history is comprised of any members that they have split off of or that split from them. A lineage may also include when a member formed or joined their system, and sometimes when they left it. A lineage could also denote that a member did not split off an existing member, walked in, or any other formation mechanism. It may also be empty if a headmate does not consider themself to have a split history.

Members that share a lineage may or may not have a familial relationship.

In some cases, lineages may progress somewhat in parallel, to the point where they can also be sorted into generations.

Subterms
The member a headmate split off is referred to as ancestor, progenian, precursor, anterian, sire, etc.

The member(s) who split off from a headmate is (are) referred to as descendant(s), seed(s), apogenian, off-shoot, posterian, scion, split, etc.

A direct lineage may only include immediate connections such as the member a headmate broke off of, and any of their own splits.

An extended lineage may include all further iterations, like their precursor's lineage, and their descendants' lineages. It may also include any members that share even part of the headmate's lineage, such as splitlings or ecliptives originating from the same initial member.

Lineages may be narrow, with each new member only splitting off the latest scion, or branching, with new members splitting off any member, or even primarily older members, or any combination thereof.

Members such as originals, cores, initials, or birthmates may be considered the root of their lineage since they have no precursor.

Lineages and Roles
Lineages may relate to a system's member structure. Literal lineages may each be associated with a specific role, with new splits taking over said role for the system, or for their current generation. As such, the lineages cooperate to take care of system upkeep. This could include a "leading" lineage that splits successors.

Longitudinal lineages may be self-contained, with each lineage having all necessary roles filled. Each lineage may form their own sidesystem, and a lineage root may hold a leadership position within that sidesystem.

Related Terms
Cataloguing lineages may be part of system mapping.

Systems that experience (primarily) non-reductive splitting may not have lineages, or they may draw lineages by other criteria, for example if their members form with a clear connection to existing members without breaking from them.