Good points, Tom. What originally inspired my comments was that I got to thinking of the classic science-fiction plot of an interstellar colony, where a ship full of settlers lands on an essentially earthlike planet and has to build a civilization from the ground up with what they brought with them. This, by the way, appears to be a prerequisite scenario for any race to spread across the Galaxy. I couldn't think of any way it could be done, even with a fleet of ships. Things would wear out, machinery would fail, and even if agriculture could be started, it would have to be done from scratch, by people who would have to be trained how to hitch an ox to a plow. (The tractors would eventually wear out.) How could they possibly bring everything, and everyone, they'd need?

Even if the local flora and fauna were edible (highly unlkely even for the most earthlike of worlds), the technological level would quickly deteriorate. When that plow finally broke, who would know how to find ore, smelt metals, and form simple Iron-Age farm implements? The grandson of the fusion plant operator from the engine room crew?

Our solar system scenario is not quite that ambitious, and the colonists would at least be able to communicate with earth, but the idea of solar system communities replacing the earth, even if cooperating and trading with each other, seems unlikely. If earth should perish, the colonies would quickly fail too.