I've been struggling with this question for some time now. A member of my family and I recently got into a debate about what is natural and what is unnatural. They are Christian so their opinion was "naturally" a warped one, but it got me thinking nonetheless.
I think that what separates us from other animals is fairly straightforward from a cognitive and technological perspective, but no one, not even the omniscient Google, has been able to give me an answer as to WHY this is the case.
Why are humans more technologically and cognitively advanced than other animals? Why are we the dominant species on this planet? Are we more evolved than other animals? If so, why have we seemed to evolve further (and faster?) than others?
On a less scientific note, do you envision a world where humans de-evolve or stagnate in their evolution allowing a new dominant species to take over?
Religion happened hand in hand with stepping away from nature. Religion has generally been an anthropocentric cultural force. Stating that nature is un-enlightened, and that humans must search for enlightenment, to rise up and away from our yucky base animal instincts. Forging society rules to regulate behaviour at the beginnings of overpopulation was essential. Fear is the best tool to keep humans in their place. Religion, through morals, has always been a tool of conformity, only necessary to ensure overly densely populated humans can coexist without killing each other. As most species are known to do in overpopulation conditions.
Religion is the very essence of un-naturalness.
I was agreeing with most of your post until this:
[...] lead to larger birth canals, which in turn lead human males to have much larger penises than the great apes. [...]
Well... religious appeals to nature are generally unfounded scientifically and essentially come from uneducated and moronic people. Humans weren't always religious. I rarely hear religious appeals to nature. All the religious people I know consider nature a vile, dirty, and dangerous place, nature is something to be afraid of. I think the religious 'appeal to nature' of the past two centuries is a reaction to the new biological understandings of life. The result of a backlash of sorts... as biological understanding of life was reaching new levels, religious people felt left out and felt they needed to demonstrate the 'logic' of the bible with 'nature talk'. In a not so different way than creationists have developed their own false-science about nature. Modern religious people want to take scientific words to describe their delusions.
I will fight them all the way on such bastardisations of language and knowledge.
And yet, we are everywhere, the most widely-distributed mammal on the planet.