Ok, since you brought up the "natural world," explain to me how lots of different species evolved from a single organism? By you're logic, we should have started out with lots of different organisms, and the weaker ones would have gotten weeded out until only the single strongest organism survived, giving it a "monopoly" on life.
Clearly this is not the case, which suggests that in the natural world competition for resources breeds variety and more competition.
You have brought up a topic that is quite involved. Let me see if I can brought up a shorter answer. You have several hypotheses, such as "from a single organism", "Clearly this is not the case", "competition for resources breeds variety". All these hypotheses cannot be explained with isolation from each other.
As much as you start "from a single organism", I can assume with the equal legitimacy that different species evolved from quite a few different organisms. Why and how have they been there? I cannot answer you, if I can, I could have been one of the greatest scientists in the world. In fact, no one can, yet. However, when life is in its lower form, it can change its DNA structure rapidly, so rapid that an environment that would terminate it also needs to evolve rapidly. Otherwise, this newer form will dwell and breed. This is one of the reasons, as well as a proof, the flu virus has different varieties every year.
Since the new individuals bearing the new variation is not necessary of a uniform collection, to extinguish the entire collection of many varieties, it needs different environmental conditions to provide different hostile "weapons". Unless the hostile environment has all kind of right "weapons" to kill, some of the individuals in the non uniform collection would have chance to stay and breed. Some of those survive may even develop some DNA nature that would command such individuals to consume its own kind to survive. See how the chimpanzee hunt the smaller monkeys for food, although both are primates. All these have planted the root for different species to appear.
Because of the "transportation" in the non human environment is so slow, two phenomena continuously races between each other in nature: developing new varieties and eliminating varieties. Which phenomenon prevails? It depends. They will arrive at a certain balance under a certain circumstance. I will not explain more, but one of the balance is that human being's over breeding has made many other living beings impossible to continue on earth. Human beings have made themselves the top predator on earth. Now, they have been preparing another fierce competition: consuming (although not directly eating) their own kind, the potential is getting stronger and stronger. The stronger and stronger potential is intensified by two elements: They gang up according to different interests and the highly develop efficient weapons in killing. In the near future, as far as what I can see, Caucasians are a losing species, because they fail to gang up.