Are Darwinian principles now extinct?

Darwin's theory of evolution is one book long, and contrary to popular representation The Origin of Species nowhere contains a succinct statement of the theory. To avoid fundamental misunderstandings, any critique of this hypothesis has to commence with what the writer understands to be the fundamental premise on which the theory is based. The essence of Darwin's theory is that there is a struggle for existence: organisms possess stable patterns of inheritance, but can develop occasional variations that interact with the environment. Those organism possessing fitter variations are naturally and specifically selected for a greater chance of surviving in order to reproduce so that, over several generations, gradual but cumulative natural selection 'filters out' the less advantageous variations of the ancestral organisms. As a consequence, new species (descendants that could only breed amongst themselves) develop.