I think that people who are appalled by the very idea that humans are a true one-off tend to be committed atheists; because if it were the case that humans are the only intelligent species would not that fact tend to favor theism over a materialistic naturalism? (Although, of course, if we were the only intelligent species, that would not be logically inconsistent with materialism.)

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"Ignorance more frequently begets confidence than does knowledge" -- Charles Darwin