Kym,
Diarmid here. On your questions of 'taking' other names it may help to
understand the fact that the modern system of surnames (what people in the US
call "family names" I think) emerged from an earlier system of
"patronymics" in
the Highlands....Meaning "father's name".
So if Lachlan had a son Dougall, Dougall would call himself Dougall MacLachlan
or Dougall son of Lachlan - and then if Dougall had a son Lachlan, this Lachlan
would be known as Lachlan MacDougall. If Dougall had a son Duncan he would be
Duncan MacDougall but his son Archibald would be Archie MacDonnachaidh (Gaelic
for Duncan).
Now with families who came to be granted responsibilities in the lands to which
they belonged, there was a need for generational continuity and so these began
to hold onto the patronymic of the founder of the family who was first 'eponym'
or the one from whom the name was taken because he was the first of the family
of that branch, or the first of the family to hold the responsibility for the
people on the land to which they belonged.
For example my own family appaer to descend from one Duncan 'Sceodnasach' or
Duncan from Ardsceodnish (now Kilmarton) who was younger brother of Sir Colin
'iongantach' (wonderful) of Lochawe who died in 1412 or 14. Duncan appears as
a young witness in Ardsceodnish (pron. ArdSCOTnish) in 1355.
Because the family were granted Fraoch Eilean Castle on Lochawe and then in
1470, the responsibilities for the people on the lands of Inverawe, Lerags and
Stronchormaig, They used the name MacConnochie (Argyll pronounciation of the
Gaelic MacDonnachaidh - sons of Duncan) as their familial patronymic.
So you would get Archibald M'Couyl (MacDougall) MacConnochie of Inverawe in
1493 and his son was called Dougall MacGillespic (son of Archibald) but not
MacConnochie until he was head of the family - although that part varied.
Sometimes they even gave the grandfather's name so as to clarify things - as in
Archibald MacDougall VicGillespic.
But for those who were not responsible for more than their immediate family -
except when called out to defend their homes with their kindred or Chief - the
use of a surname only began to come in with the use of records - first church
records and court records. By the 17th century most had adopted surnames I
would think - but in the 16th century they were still not common.
Even the sons of Dougall who were Lords of Argyll did not call themselves
"MacDougall" often, but "de Ergadia" or "of Argyll" or
"of Argyll and the
Isles".
I hope this is some help, Diarmid