Everyone and thing comes about becuase of a cause. Aliens could not have “evolved through completely natural purposes”. (This in no way means I believe in aliens, but I am just continuing your analogy).
In the end God would have to have at least guided the aliens evolution, though I would say that if here were aliens more like he would have ‘created’ them through miraculous supernatural power. I don’t believe in aliens, but I do believe mankind was created through miraculous power.
Evidence exists in God being our creator, and the worlds, there is no evidence for aliens.
You don’t fool me young man! It’s turtles ALL THE WAY DOWN!
Have you, by any chance, read this book: Aliens: The Final Answer? a Ufo Cosmology for the 21st Century by David Barclay http://www.amazon.com/Aliens-Final-Answer-Cosmology-Century/dp/0713724986/ref=sr_1_1?ie=UTF8&s=books&qid=1207595619&sr=8-1
My point is this: once you start talking about an entity that created humans and the Earth, you are conceding that that entity is “supernatural”-—super = above + natural = the natural laws of “science”.
Generally, a supernatural entity would be defined as a “god,” in the sense of being more powerful, more intelligent, etc. than its own creation. (So I’m not talking about a “god” as something that must be worshipped and all that.)
Once the existence of a god is conceded, then you have to grapple with whether god constitutes “God,” that is, not only a supernatural entity, but a supernatural entity that has moral authority over the destiny of its creation and the ability to “steer” its creation according to its will.
It seems to me that by saying maybe we were created by “aliens,” you are conceding the existence of a supernatural entity-—a god or gods.
That being the case, it seems to me that you actually are disagreeing with the author’s conclusion that the supernatural entity that created humans and the Earth and all that is in it is “God”-—i.e., a supernatural entity with moral authority.
I’ve often found that people who deny the existence of God do so because, at bottom, they reject-—or at least want to avoid grappling with-—the possibility that a supernatural entity with not more power (the power to create something from nothing), but superior moral authority exists. And, therefore, might subject its creation to moral judgment.
IOW, the sticking point that motivates many of those who reject the existence of God actually is not about whether God created creation, but about the fact that such a creator would (or at least might have) the power and desire to impose moral judgment on them.
If a person does not want to be judged for how he lives his life, one way to “convince” oneself that he can live as he pleases without anything other than “natural” (as opposed to supernatural/eternal) consequences, is to reject the existence of the Judge in the first place.
So, you see, by conceding that a supernatural entity might have created humans and the Earth, you still end up having to grapple with the existence of God and his authority.