Darwinism is unquestionably the reigning scientific paradigm of our day. As we celebrate the sesquicentennial of the publication of Charles Darwin’s Origin of Species, we are reminded of his ingenious proposal that ignited the imagination of nineteenth century moderns. These intellectual progressives were in search of a non-theistic theory of life that supported their commitment to the sufficiency of human reason and their resultant utopian optimism about human progress. Darwin obliged them by proposing a purely mindless naturalistic process so apparently reasonable and so elegant that it was love at first sight. It is called natural selection.
        
        Natural selection is that method by which nature allegedly preserves advantageous anatomical, physiological, and/or chemical changes or variations that occur randomly within an individual animal of a particular species. As a result, the animal’s offspring exhibit and enjoy progressively increasing survival benefits over competing animals of the same species. Over time, the animal and its descendants overtake their disadvantaged brethren in the survival race, the latter moving toward inevitable extinction, the former emerging as a victorious new kind.  

         It is important to understand that Darwin envisioned this process as occurring not simply within unchangeable species. In fact, Darwin argued that species were not unchangeable as had been previously held. According to Darwin, random variation followed by natural selection was the process by which all of the many and varied animal body plans and the innumerable species descended from a single common ancestor. Furthermore, these changes required long periods of time, perhaps many millions or even billions of years. 

        His theory predicted that the fossil record in the geological strata should reveal an extremely gradual appearance of animal body plans. In other words, the major body plans that define the highest taxonomic classifications (phyla) should appear in the fossil record at the end of long, identifiable, and branching lines of descent. These descending lines would exhibit an abundance of more primitive transitional animal forms inching their way by incremental steps over many millions or billions of years toward their current observable status in the animal kingdom. Darwin asserted,     

        "If the theory be true, it is indisputable that before the lowest [geological] stratum was deposited, long periods of time elapsed, as long as, or probably far longer than, the whole interval from the age [of the lowest stratum] to the present day, and that during these vast, yet quite unknown periods of time, the world swarmed with living creatures" (Charles Darwin, The Origin of Species, [1859], Penguin Books, 1985, 313).