Why Genealogies?

[Lalwendë]

Maybe the lawyers had some responsibility for record keeping? There was obviously some form of administration but not a 'state' as there was little need for control (few external threats and abundance of resources).

It all adds to my long-held impression that The Shire is a very different and much more modern place than the rest of Middle-earth. Rohan is still operating like an Anglo-Saxon society with portable wealth and something like 'wapentakes'; Gondor is like a feudal city state in stasis; and the Elves in some kind of pre-historic society (all very debatable of course - this is just a quick glance at the contrasts). While The Shire has a postal service, 'museums', lawyers, complex inheritance customs, developed trade, an elected Mayor, even a rudimentary police force. It always reminds me of a highly idealised view of Edwardian England without the heavy industry or intense poverty...I digress....

The position of Thain was inherited, and though the Thain wasn't an 'aristocrat' by any means, and more like a titular steward in control of any military needs, no doubt it was still an honoured position and it would be important to keep track of who was in the line of succession. Pippin had sisters who were older to the best of my knowledge, so it looks to have been inherited through males only - another reason why they would need to keep an eye on the family tree!