an oversimplification, as Gaelic-speaking tacksmen and drovers were to be found in the sheep trade from the 1780s. When sheep were introduced in the Sutherland Clearances, over half the leases were taken up by Sutherlanders. Clanship Since their origin in the early Middle Ages, clans were the major social unit of the Highlands. They were headed by a clan chief, with members of his family taking positions of authority under him. The mechanisms of clanship gave protection and agricultural land to the clansmen, who in return paid with service and rent which was paid, especially in earlier periods, mostly in kind (as opposed to money). Service included military service when required. The Highlands was one of the parts of Scotland where law and order were not maintained by central government, hence the need for protection from a powerful leader. Clan leaders controlled the agricultural land, with its distribution generally being achieved through leases to tacksmen, who sublet to the peasant farmers. The basic farming unit was the or township, consisting of a few (anything from 4 to 20 or more) families working arable land on the run rig management system, and grazing livestock on common land. Clans provided an effective business model for running the trade in black cattle: the clan gentry managed the collection of those beasts ready for sale and negotiated a price with lowland drovers for all the stock produced on the clan lands. The sale proceeds were offset against the rentals of the individual producers. The growth in the trade in cattle demonstrates the ability of pre-clearance Highland society to adapt to and exploit market opportunities—making clear that this was not an immutable social system. James VI was one of the kings who sought to impose control on the Highlands. On becoming James I of England in 1603, he gained the military force to do this. The Statutes of Iona controlled some key aspects; this forced the heirs of the wealthier Highlanders to be educated in the Lowlands and required clan chiefs to appear annually in front of the Privy Council in Edinburgh. This exposed the top layer of Highland society to the costs of living in Edinburgh in a manner fitting to their status. Unlike their Lowland counterparts, their lands were less productive and were not well integrated into the money economy. Large financial sureties were taken from clan leaders to guarantee the good behaviour