The two are fraternal twins, born of a mother who swims up to the shore of the island after her ship is wrecked. She's shortly killed by a woman already on the island, who raises the twins as her own. The significant and increasing difference between them is the boy with dark hair who grows into the man wants to leave the island. Jacob does not.
MIB - who isn't fully the MIB as yet - leaves his faux-mother, to live with a group of people on the island. They've discovered that certain places on the island have magnetic properties. Eventually, the almost MIB discovers that with the right equipment - including the big wheel with spokes - someone can leave the island. But before he has a chance to complete the structure, his faux-mother knocks him out, burns the well, and kills all the other people. When she comes back to him the next day, he kills her.
Jacob, who never wanted to leave the island, but who resented his "mother"'s greater love for the almost MIB, was activated by his "mother" as her successor and the island's protector before she went to see MIB on the day that he killed her. Jacob, understandably none too happy about that, drags the almost-MIB to a place their "mother" has briefly shown them, years before: it's the magical energy source (unless aliens made it) that animates the extraordinary powers of the island. Jacob throws his brother into it. The brother's human body dies, and the smoke monster emerges.
So, at some time in the future which we did not see, the smoke monster will inhabit the almost-MIB's dead body - just as it did with dead Locke - and the almost-MIB will walk and live on the island, now the full-fledged MIB, with an implacable hatred of Jacob and an implacable desire to leave.
My take: with the exception of Lord of the Rings and Harry Potter, I've always liked science fiction much much more than fantasy, and this sure wasn't a Lord of the Rings. The breathtaking parts of Lost for me, in addition to the compelling human stories and the stunning plot intersections and weavings, were the science fiction - in particular the time travel, a la Desmond and Daniel in their own ways.
I'm looking forward to more of that next week, and in the finale beyond.
6-min podcast review of Lost
See also Lost Season Six Double Premiere ... Three Questions Arising from the Lost Season Six Premiere: Linkage Between Two Realities, Dead Bodies Inhabited, Who/What Survived H-Blast? ... Lost 6.3: Kate and Claire, Tenacious Details, and Dr. Arzt's Arse at the Airport ... Lost 6.4: Better LA, Wilder Island, Some Partial Answers at Last ... Lost 6.5: Jack's Family and Prester John's Speculum ... Lost 6.6: Sayid the Assassin in Both Realities ... Lost 6.7: A Better Ben in Both Realities ... Lost 6.8: The Third Team ... Lost 6.9: Richard's Story ... Lost 6.10: Cloudy Sun ... Lost 6.11: Reunion of Two Realities Begins ... Lost 6.12: Libby and Hurley and Cross-Reality Communication ... Lost 6.13: Make-Up, Break-Up, Everything is Shake-Up ... Lost 6.14: Jack's Tears
and Preliminary Predictions for Lost Finale
More Lost - see : The Richard-Locke Compass Time Travel Loop ...
and Lost Returns in 5 Dimensions and 5.3: The Loops, The Bomb ... 5.4: A Saving Skip Back in Time ... 5.5 Two Time Loops and Mind Benders ... 5.6 A Lot of Questions ... 5.7 Bentham and Ben ... 5.8 True Love Ways ... 5.9 Two Times and a Baby ... 5.10 The Impossible Cannot Happen ... 5.11 Clockwork Perfect Time Travel ... 5.12: Ben v. Charles, and Locke' Slave ... 5.13: Lost Meets Star Wars and the Sixth Sense ... The Problem with Baby Aaron and the Return of the Oceanic Six ... 5.14: Eloise, Daniel, and Obsession Trumping Paradox ... 5.15: Moral Compasses in Motion ... Lost Season 5 Finale: Jacob and Locke
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book