I believe that the island is from the future. Lets take the 4 toed statue for instance, it is proven that through evolution that if humans come to lose a body part it would be the small toe as we have no use for it. It was also hinted to take note of how many toes Richard Alpert has where I previously read somewhere. So in theory i believe that Richard Alpert and the statue have come from the a future time/space and have obviously with the island traveled over time to where the island is now.
The reason I believe John Locke is Jacob is because if the island is from the future and has traveled back over time, then we know that at some point in the future Locke will be dead. If you remember the 1st time Locke went to Jacobs cabin he was unable to see Jacob, this in theory is because he is Jacob, and Jacob knows what to do because he has already lived through it and can now tell his past state what to do. I may have not worded this very good, but I believe it to be true and when it comes to a point in the Lost series where we find this out, this will be when Locke's life will come full circle.
Theory by Dan
The reason I believe John Locke is Jacob is because if the island is from the future and has traveled back over time, then we know that at some point in the future Locke will be dead. If you remember the 1st time Locke went to Jacobs cabin he was unable to see Jacob, this in theory is because he is Jacob, and Jacob knows what to do because he has already lived through it and can now tell his past state what to do. I may have not worded this very good, but I believe it to be true and when it comes to a point in the Lost series where we find this out, this will be when Locke's life will come full circle.
Theory by Dan