There was an experiment in your timeline: the effect of high oxygen concentrations on insects. Even modern dragonflies get bigger, given that bracing atmosphere. Cockroaches don’t. Roaches grow more efficient instead, able to devote less of their biology to the quotidian graft of transporting O2 to their tissues. They find room for bigger muscles, more efficient guts, a higher energy metabolism, more complex behaviour.

I told you you wouldn’t like it.

In these Carboniferous forests, one species of cockroach happens on the evolutionary advantages of communal living. First it influences just mothers and their broods, linked by a chemical communion. This proves sufficiently advantageous that each generation improves upon the recipe, and populations explode over a few million years into super-colonies. These contain hundreds of thousands of insects that, regrettably, already look a great deal like the roaches you so dislike. If you were minded to look closer, you’d see that they are already morphing into distinct castes. There are workers with specialized mouthparts, and guardians whose form suggests that cockroach cousin the praying mantis. In this timeline, they are filing patents on behaviour patterns that ants adopt two hundred million years later in your world. They are cultivating fungus gardens, growing antibiotics and forming partnerships with plants where they fight off predators in exchange for a packed lunch. They build enormous air-conditioned nests that put termites in the shade. The most successful lineage soon goes global, able to tailor its behaviours to the precise climate, temperature and biome that it finds. And then it tailors the biome to fit its preferences.

So when does intelligence arise, precisely? At what point does all this complex but mechanistic behaviour approximate thought? There is no I anywhere in this world-spanning colony, yet as time races on, they shape the world to their wishes without any individual unit being aware of it. And when the Permian dying times come for them, they are ready for it. Each change in the Earth’s temperature and climate and chemical balance is noted, as Death tries to play Grandmother’s Footsteps with them. A worldwide chain of experimentation and decision-making is set in motion, a system that feeds information in and gets action out. This species stays on top of environmental changes without falling off the path, neither too much nor too little. It guides the Earth through the Permian deathtrap, without getting a scratch on the paintwork.