You are REALLY stuck on this 'lower life form' business. Try changing your terminology a bit.
Cerin wrote: And does this theory of 'natural selection' lead to the notion that all species evolved from simpler life forms? Because that is the idea I think most people are referring to when they talk about teaching 'evolution'.
Quote: The theory of "evolution" ... is a misnomer. Darwin did not use this word for his theory. His theory is the theory of "natural selection."
The origins of humanity cannot be proven by science. Period. The origins of humanity are not observable. We can make speculative guesses about how human beings came about, and use those as theories against which hypotheses can be made, but it can never be proven using scientific method that humans came from anything other than humans.
The CURRENT theory is that human being came from a similar ancestor to chimpanzees or something (monkeys? I dunno). There are scientists working to DISPROVE this theory, not prove it. They attempt to disprove it by collecting evidence of historical migration patterns, body structures, DNA analysis (when we can get it), and other information. So far, no one has been able to disprove that humans came from this common ancestor, although they HAVE managed to narrow down a few branches from that family tree we DIDN'T come from. Now, where did this common ancestor come from? Beats the hell out of anyone. They have theories for it, though, and are trying to disprove those too.
For people to suddenly stand up and go, "We know the answer," (as many intelligent design people seem to be doing) is a bunch of bullshit. They don't KNOW anything, they believe it. They have faith. Bully for them. They have faith in something, but very few have faith in them or their faith (because it isn't a theory because you can't prove it wrong). Scientists want to prove something wrong and what they are offering cannot be proven wrong any more than it can be proven right so please pardon scientists if they ignore the inappropriately named intelligent designers and go back to doing science while the preachers go back to preaching whatever it is they believe. I hear the giant spaghetti monster is big these days.