As for the "scientific community," it probably is not easy to define but isn't that hard to identify. In fact, I think a good shot at a definition might start with academic scientists and the authors of papers in journals they respect, and fan out to include scientists working in government or industry. "Outsiders" are not hard to spot: someone building a perpetual motion machine in his garage, people banding together to form their own small communities specifically because the scientific establishment rejects their work (think cold fusion and the Discovery Institute).
Now this kind of definition may sound awfully presumptuous, but only if you buy the notion that what the scientific community endorses at any given time is The Truth! Sometimes the established orthodoxy is overthrown, usually from within the community (a Kuhnian revolution). The fringe people are the kids who don't like losing the game and announce they're taking their ball and going home. Does this in itself imply that their ideas are wrong? No. But in far, far more cases than not, their work does not pan out, and the scientific consensus prevails.
(The romantic notion of the lone genius creating breakthroughs for which the establishment simply is not ready sustains many of the fringe people. But if you press them for historical examples of people who we rejected by the establishment but were proven right in the end, you tend to hear names like Galileo. Certainly there was a rejection, but the authority behind it was certainly not a scientific community!)
Concerning evolution versus the various flavors of creationism, I think there's actually a serious problem with the idea that evolution is a scientific theory. Suppose one tries to apply Popper's notion that scientific propositions must be falsifiable. What finding could possibly invalidate evolution driven by natural selection as the template for any more detailed account of how species emerge or go extinct? It's a principle on par with, say, the assumption all scientists make that the natural world operates according to principles we can discover or formulate, and does not capriciously change in ways that render science itself impossible.
This is why no version of creationism could ever possibly be part of a science of biology. To appeal to deities and designers is nothing less than giving up scientific explanation. (
"Magic Man done it?") Natural selection as a principle simply is essentially THE scientific way to understand life.