The center of a black hole, which is a singularity in the approximate theory of general relativity- it's an approximation because the singularity is a Planck region- actually is thought to be separated from the region just outside the singularity by a memberane. Inside the membrane is the unified field. This is an actual 3-d membrane, not one of those higher dimensional membranes of string theory.

Smolin proposed that baby universes can separate from inside the membrane, without going outside of it, but rather by creating new space in new big bangs that we never see in this universe. Brian Greene in his book "The Elegant Universe" has make believe pictures of how that would happen.

If you look at those pictures, it does look like the new baby universe is contained within another membrane. But that is probably just because the pictures are make believe. But other than that, the essence of your theory is correct. Black holes probably make new universes.

Smolin takes this a step further. Since black holes make new universes, then the new universe that makes the most black holes will be the most prevalent universe. And after a long time, such universes will probably be the only ones around. That's an evolution that has already happened.

So his theory is really not that universes evolve. It is more like the anthropic principle that the universe we live in is the only kind that exists, even though an infinity of them may exist

Hope this helps.

Wanda