Food chains and Evolution

Most food chains have a major predator at the end, who are not preyed upon. Their numbers are few and their population is finely balanced because of competition, and lack or presence of preys(food and milieu both actually). Most of these predators, e.g. pumas, leopards, polar bears, sharks, are also confined to a few food webs. Humans on the other hand, form part of almost every food chain, not only because they can eat anything but because they inhabit almost every corner of this world. We also are at every level of a food pyramid, since we eat plants, insects, reptiles, mammals. Hence there is neither any competition for food or space, and the species growth is almost unchecked. The big predators can kill and eat us but we rarely give them a chance. The world population is estimated to be about 6.5+ billion, there might be more humans than ants, if you ask me.

As evolution occurred, the higher forms of life survived (devoured) on the lower ones. Atleast in the animals' cases. So at every level in the food pyramid there was a balance. The humans' case is like an exception. So how does nature go about balancing this anamoly. Either by restricitng the food and space needs of humans. This might soon happen with the way we are growing. Many parts are already facing food shortages. The other option is,a being that preys on us, evolves. Evolution is a slow process, and we might not see a different species till another million years. It might be though, that a world food crisis accelerates this evolution. After all, it will be survival of the fittest.