In the Creatures artificial life / virtual pet series, the creatures have about 900 (maybe more in later versions) or so neurons. Each neuron is a little virtual machine that is designed in such a way that programs remain valid even with random mutation.
A friend of mine made this in-browser neural network engine that could run millions of multi-layer NNs in a simulated world at hundreds of updates per second and each network could reproduce and evolve. It worked in the sense that the networks exhibited useful and varied behaviors. However, it was clear that larger networks were needed for more complex behaviors and evolution just starts to take a lot longer.
There is the case of Blondie24, an evolutionary neural net, or genetic algorithm, which was able to develop a very strong checkers-playing capability by self-play with no human instruction. It was later extended to paly other games.
presumably because it's saturated with a monoculture, and the hope (rightly or wrongly), some of the other roads might lead to some alternative breakthrough.
Among the many uses, they have been applied to ‘evolving’ neural networks.
Famously a guy whose name I can’t remember used to generate programs and mutations of programs.
My recommendation if you want to get into AI: avoid anything written in the last 10 years and explore some classics from the 70s
[1] https://en.m.wikipedia.org/wiki/Evolutionary_algorithm