Spiders (I'm not sure this is all of them) have to liquify their food because emergence placed their brain around their throat. As the brain grew it restricted eating in a rather nasty feedback situation.

A literal bottleneck in one way, but also one that prevents further emergence.

But I agree that our human bottleneck is cultural. Our bodies haven't had much time to further emerge, in only 3000 iterations.

You can't be me, I'm taken