The term "survival of the fittest" is a well understood phrase that has its root in Darwinian evolution theory as an alternative phrase for natural selection. The idea is that "natural selection" means that the fittest form is the one that can reproduce the most successfully to make the most copies of itself in successive generations.
The process of natural selection is understood to mean that over time, nature will support those beings with a superior DNA make up, where their advantage helps them to leverage energy from the natural resources and overcome natural threats and predators. Weaker versions of a species will eventually be overcome by the stronger versions - the fittest survive.
However, if we consider the modern day planet we live on, things have changed. The animal kingdom is now at the mercy of us - the dominant species. For most natural habitats, survival is no longer down to the process of natural selection but rather their survival is dependent on us making a choice to let them carry on existing. Our technology and knowledge give us power over the animal kingdom and we are able to dominate the world.
Further, most of the mammals in the animal kingdom only exist because we want them, for food. We allow them to use land so that we can farm them and eat them. It is nothing about the strength of their genetic profiles or how they are stronger than their predators. They survive because we protect them and help them reproduce.
So what about us? Is our human species still governed by natural selection? It is not the case that those with the strongest genes are necessarily the ones that are reproducing more successfully. Money and power make the world go around. The ones with money and power can protect their progeny in a dog-eat-dog world and use their influence to help ensure their offspring survive better in this world. It is more like an unnatural selection where some of the most powerful people in the world are some of the weakest amongst us. Yet their money and power protect them. We have moved beyond biological selection.
One could of course argue, that this too is a form of natural selection, that we have developed our cognitive abilities through evolution to the extent that our brains are what make us the kings of the jungle. My point though, is that we have moved far beyond what Darwinism was orignally describing.
In the end, I believe that the age old laws will once again come into full effect and take control of this planet fully again. We are like the bacteria in a petri dish that don't understand that the more we consume the resources of this planet, that we are just accelerating our eventual demise. When society collapses, once again, the forces of nature will take hold and ecosystems will be restored through a process of "survival of the fittest".
If only we could be intelligent enough to use our intelligence to help preserve our ecosystems and the planet. To provide a world where nature can coexist with us living in a sustainable fashion. We would then be worthy of a title like "king of the jungle".