The best explanation for the theories of natural selection is that

The theory of natural selection proposes that organisms with favorable variations that enable them to better adapt to their environment have a greater chance of survival and passing on their advantageous traits to their offspring. This means that not all organisms have equal capacity for survival in their habitats. Instead, organisms have varying capacities for survival based on their ability to compete for resources and adapt to their environment. Better competitors are more likely to survive and thrive, leading to the evolution of more fit and adapted organisms. Therefore, the best explanation for the theories of natural selection is that organisms have varying capacities for survival in their habitats and that organisms compete for resources, with better competitors being more likely to survive and thrive.