The following was primarily extracted from the book Clan Davidson compiled by Alan McNie.
According to the Highland manuscript believed to be written by one MacLauchlan, bearing the date 1467, and containing an account of the genealogies of Highland clans down to about the year 1450, which was accepted as authoritative by Skene in his Celtic Scotland, and believed to embody the common tradition of its time, the origin of the Davidsons is attributed to a certain Gilliecattan Mhor, chief of Clan Chattan in the time of David I (1085 – 1153). This personage, it is stated, had two sons, Muirich Mhor and Dhai Dhu. From the former of these was descended Clan Mhuirich or MacPherson, and from the latter Clan Dhai or Davidson. Sir Aeneas MacPherson, the historian of the clan of that name, states that both the MacPhersons and the Davidsons were descended from Muirich, parson of Kingussie in the twelfth century.
Davidson Clansman - A Watercolor Print by R.R. MacIan circa 1845