ok... for one thing, spontainous creation of life has NEVER been observed. Define "better defences". They have adapted biologially, with the bacterias who's DNA codes for the specific protiens that make them immune taking prevalence over the bacteria that lack the gene.

Imagine if you will, a pack of wild yorkshire terriers (absurd bacause yorkshire terriers are pretty much artificial dogs created as you mentioned by years of selective breeding). If you let a pack of yorkies out in the wild for a thousand years.. assuming they survived, would they ever try to breed with a wolf (technically a breed of wild dog)? thus you have different "species" (the exact deffinition of wich is still disputed by biologist).

People like you do a disservice to humanity. You simply accept the simplest method as truth and stop looking and trying to discover, which is in human nature to do. If the world didn't have people who challenged the accepted norms, imagine what it would be like today?