Perhaps it's already here. In reference to a different thread about Japan's population decline, it is supposed there that advanced economies lead to population decline (via below replacement birthrates) and require immigration to sustain them. The problem is that those immigrants who choose to remain are that they or their decendents will eventually suffer the same below replacement birthrate. If everywhere becomes an advanced economy, then in theory, everywhere would suffer the same fate, and the great filter has won. But it's just a supposition, right.