I find it most helpful to think of bloodlines as environmental adaptations as much as kinship groups. They split and merge according to the fortunes of the steads and the resources they can exploit as much as through kin quarrels or family growth. A bloodline is simply an extended family, but it is also the unit of work. The steads are organised communally and clan resources are given by the chief into a bloodline's keeping. They are remarkably fluid in terms of merging, splitting and branching out. While most largish bloodlines will have a mixture of cottars and carls, rich cattle husbands and poor sheep herders, part of their herds (and therefore riches) are communal.
John
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