A Selection Theorem tells us something about what agent type signatures will be selected for in some broad class of environments. Two important points:
The theorem need not directly talk about selection - e.g. it could state some general property of optima, of “broad” optima, of “most” optima, or of optima under a particular kind of selection pressure (like natural selection or financial profitability).
Any given theorem need not address every question about agent type signatures; it just needs to tell us something about agent type signatures.
For instance, the subagents argument says that, when our “agents” have internal state in a coherence-theorem-like setup, the “goals” will be pareto optimality over multiple utilities, rather than optimality of a single utility function. This says very little about embeddedness or world models or internal architecture; it addresses only one narrow aspect of agent type signatures. And, like the coherence theorems, it doesn’t directly talk about selection; it just says that any strategy which doesn’t fit the pareto-optimal form is strictly dominated by some other strategy (and therefore we’d expect that other strategy to be selected, all else equal).

From: Selection Theorems: A Program For Understanding Agents