According to this interpretation of origins, all organisms currently living have descended from one or a few original ancestors through a process of random change over long periods of time and this was possibly brought about by natural selection. But as you will note when reviewing natural selection, and mutation, neo-Darwinism cannot explain the arrival of new body plans so it is without merit in explaining the diversity/disparity of creatures. Nor can it explain the origin of life itself. Furthermore, most scientists today find that neo-Darwinism is not that useful an explanation for how the diversity of life came about, because neither horizontal gene transfer nor convergence fits the neo-Darwinian idea of descent with modification.
Neo-Darwinism has outlived its usefulness as an evolutionary explanation for where the major body plans came from.