Hello everyone, not so long ago I found this map while browsing the web: https://s-media-cache-ak0.pinimg.com/736x/a7/2e/a5/a72ea552bee0b693907b9b25491d19e1.jpg and while I don't know how true it is it led me to ask myself why do the spanish and the portuguese use two surnames when seemingly the rest of the world mostly uses the father's name only (I was born in a spanish speaking country and it is my mother tongue). I tried searching for answers on my own but other than discussions on the legal implications of the naming customs I couldn't find a reason for why it started. My uneducated guess would be that it had something to do with the inheritance of noble titles as an easier way to keep track of the families involved, but I have found no evidence as to what the real reason was.
In medieval England, the choice of a surname might not be Fitz Gerald but Fitz Isabelle, or Baxter/Webster rather than Baker/Webber because Mom was the notable parent and a baker or weaver. It did not indicate illegitimacy. It used to be pretty common in the USA to give children their mother's family name for a middle name. It is now customary in one-child China to give the child its mother's family name as its given name.
The medieval Basque, before they had family names, would be recorded in official documents Sancho, son of Urraca, not Sancho, son of Sancho - matronymic, not patronymic.
LSS, the giving of names is an arbitrary custom. Women's family names are not always ignored. In the case of Iberian names, Basque may have influenced the importance of matronyms. So may the habit of women keeping their family names on marriage.
Source: Ingraham, People's Names, McFarland, 1997
