Clan Gunn patronymics
Many Scottish surnames originated in patronymics, whereby a son’s surname derived from the father’s forename, e.g. John Donaldson’s son might be Peter Johnson, whose son might be Magnus Peterson, and so on. Patronymics present something of a challenge for the family historian in that the surname changed with each successive generation. This practice died out in Lowland Scotland after the 15th century, as patronymic surnames became permanent family names. It persisted, however, in the Highlands & Islands well into the 18th century...
 From Scotlands People http://www.scotlandspeople.gov.uk/Content/Help/index.aspx?r=551&560 accessed 1 May 2014
We are meant to believe - according to Clan Gunn mythic history beloved by Clan Gunn Societies - that the surname Gunn originated from the Orkneys in the early 1200s and the surname directly flowed from one man when, according to the above, fixed patronymics basically did not exist in the Highlands and Islands till the 1700s. Lord Lyon also states 'surnames were generally adopted in Scotland in the 17th century' ('Coat of Arms and Crest Badges booklet' 2012).
The only sensible logic for the surname Gunn is that presented by Smibert. The Clan Gunn Orkney origin non-link I have dealt with often on this site.