In my opinion, Jason looks like he could be Jack's younger sibling. Could he be? Here is why I believe this.
-This island is (as I made it earlier) almost obvious that this island is FarCry 1's.
-UbiSoft stated that Jason Brody has a brother on the island.
-Ubisoft also said that they are connecting Farcry 1 and 2 in this game.
-Jack Carver and the Jackal are who I think to be the same exact person
I know this thread is about 2 years old but if it helps any,I've got a theory... Remember in FC3 Citra narrates a story to Jason.... about a beast that haunted the islands/waters,she mentions about a warrior who was brave enough to cut the beasts' head off with ease... Now ... I'm pretty convinced that the 'beast' is actually one of Dr.Krieger's insanely mutated trigen... and the warrior who cut it's head off.. isn't it obvious??the warrior's none other than Jack Carver... his descendants are the Rakayats,they're not as smart or as cheeky as Jack but they're foolishly brave and that's enough to make an assumption...