Well, that's certainly a different perspective. I agree that the mind is bound up with its environment in lots of ways, but I don't know if that constraint explains the moral forms of the Axial Age. Even if the geomagnetic fluctuations were relevant to culture, the question would remain about the cultural contents' emergent status. Are the moral reforms still valid? Is the theology true, or does it succeed on an aesthetic level?

You seem to dismiss the philosophical questions as vacuous or as of lesser importance than the scientific models. I'm pretty sure, though, that philosophy, art, and science aren't addressing exactly the same questions, so there's not such a conflict between them. Philosophy simplifies and generalizes to give us an overall view of where we stand. A scientific model like the one you propose would account for a narrow question of causality, of why collective spikes in cognition occur in specific periods. There are always multiple causes, though, so we'd need a broader perspective to assign the right weight to each of the causes. And then we'd be getting into philosophy.