Martin, Larger brains in earlier modern humans may not indicate that they were "logical, sceptical empiricists." Even if a larger brain necessarily meant greater mental capabilities, the larger brains of Cro Magnons (for example) could just as easily have been better at religious thinking, as at logical thinking. But a large brain doesn't necessarily mean greater mental capabilities. If it did, men would be, on average, about 10% more mentally capable than women, and I don't know of any evidence for that. While it's possible that our mental capabilities are inferior to those Cro Magnons had, it's also possible that our brains now have greater spatial efficiency, with no big change in mental ability relative to earlier modern humans.
That said, I don't really take issue with anything else you said. I would only like to add that I think religion is a manifestation of some very useful human mental characteristics. I think its origin must be in our attempts to use verbally-based abstract and symbolic thinking to explain those periods when our focus is so absorbed by an object, an activity, or our general environment, that our internal monolog shuts down and our verbal record of events goes spotty or totally blank. Such an experience can make one feel like one has left one's body, or has been taken over by another being. If some insight comes from the experience, it may seem to have come from an outside source. Only recently, with our modern philosophy of science, has it come to seem so improbable that trance-like states and the insights that come from them could have non-natural origins. Finally, I'll just say that you could be right about modern humans being less rational, more religious, and generally not as smart as our paleolithic ancestors. One big evolutionary advantage of organized religion is that it gives great power to the group. The people in tribe A might be smarter, but the people in tribe B are more unified in their purpose, so they are more likely to win if war breaks out, allowing them to displace tribe A. Meanwhile, within tribe B, individuals who don't subscribe to the dominant religious viewpoint (including those who do not feel spiritual and those who see through the priesthood's manipulations) are much more likely than average to be killed or cast out from the group. Thus, highly rational, skeptical individuals would have low relative fitness within a tribe with many religious types, and tribes dominated by free-thinkers would be displaced by tribes with a strong priesthood. Just throwing another just-so story on the fire. Jim Crants
