On 108b based on Tosafot Sof Divrei Hamatchil Yachol (the first one), the Gemara's question of 'Ma Ra'Ita L'Rabot Et Ha'ben' is why should the order of yerusha be son, father, brother, why not the opposite brother, father, son,
But according to the Rashbam Divrei Hamatchil Ha'Karov, Karov where he says its Peshita to the Gemara that a son precedes a father, what is the gemara's question of 'Ma Ra'Ita' --> instead of son, father, brother it should be brother, son, father (since son must precede father according to the 'Peshita' in the Rashbam) then what is the chidush of 'She'Ero', that the father should precede the father's brothers, that the gemara on 109a says is peshita - 'Lo Tzrichi Kra'.
Simon Wolf, Westport, CT
The Rashbam that you mentioned is preceded and followed by two other Rashbam's:
In DH Yachol, Rashbam writes "Yehei Ya'akov Kodem l'Chanoch ben Reuven." That is, Rashbam was also learning that the question at the "Yachol" stage was that the father should be first. This is learned from "She'ero," which would mean, if not for "Hakarov," that we should place the father first even though he is not the closest relative.
What the Rashbam DH ha'Karov refers to as "Peshita" is that when we are learning precedence in Yerushah from "ha'Karov" , it is obvious that the father does not precede the son. We will learn, however, that the father is second from She'ero -- with only one other relative preceeding him, as learned from ha'Karov.
Rashbam then explains the Mah Ra'isa (DH u'Mah Ra'isa) that the question was why did we use ha'Karov for the son (which makes the order son, father, brother); we should use ha'Karov for the brother (which will make the order brother father son, as Tosfos explains).
Again, it is only obvious that the son precedes the father as relates to the Pasuk of "ha'Karov."