Your train of thoughts seems to be as follows:

1. Only code that has already a cognitive capacity far beyond that of an insect or a toddler is able to evolve itself.
2. As we do not have a theory of thought, even for simple organisms, therefore creating software that thinks is beyond our capacity.
3. Therefore we can’t either create a strong AI ourselves, nor even lay a seed that would be able to evolve itself.

That sounds a bit like the chicken or the egg causality dilemma. As there is nobody who truly understands intelligence nobody can create intelligence.

The evolutionary biology provides literal answers with the Darwinian principle. Species evolve over time, and thus chickens had ancestors that were not chickens — intelligent machines will have ancestors that were not intelligent or did understand what intelligence is.

And it has happened before — here we are, intelligent humans evolved from unintelligent cosmic matter.