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.

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.

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

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.