A cathedral of rhetoric, it has been build from the top down - an overarching theory supported by further theories reaching not into establishment, but into postulation. That is not to say aspects have not been proven true by any means.
Darwinism is a theory of the development of biodiversity driven from two central tenets:
- Natural Selection
- Common Descent
It presents that all life originated as a simple, aspecific life form (such as a simple bacterium) and that, through gradual accumulation of minute changes, current life forms changed and adapted to various environments and challenges, diversifying into new species. It says nothing about the origin of that first seminal life form, merely the progression therefrom.
The law of natural selection presents that:
- Variation exists within a population
- Individuals with variations more advantageous to the environment are more likely to survive and pass on their traits
- Gradually, the population will shift to the more favourable form
The theory of common descent suggests that all life originated from a single organism.
Of the two, natural selection is well-documented and proven, being established into law.
Back to the original comment, however, Darwinism is in bad shape. The theory of diversification via accumulation is yet to solidify as anything more than theory.
Through the 19th century, much of the discussion pertained to the fossil record and its incompleteness. Many theories supporting Darwin's theories were suggested, each reliant upon further fossil discoveries. Then came the cambrian explosion. Massive numbers of fossils of great diversity were found in a stratum of rock ranging 55 million years, which is an extremely short time, evolutionarily speaking. This discovery rocked the palaeontological world with its great diversity and apparent lack of transitional or predating forms, leading many to further suspend the theory for yet undiscovered, earlier fossils.
Enter the ediacaran fossils.
These precambrian fossils presented a possible closure to evolutionary theory, but many palaeontologists expressed doubts that many, if any, of these fossils are actually precursors to those found in the cambrian strata.
Shelving the fossils, many turned to structural systems, suggesting that analogy indicated evolutionary similarity. From this set of theories, species with greater similarity branched later on the evolutionary tree than those with fewer similarities. As far as theories go, it was actually quite decent and, aside from the hitches throw in from convergent evolution (why would species diverge, then converge again in form?).
In the 20th century, studies on mutation presented a possible mechanism for variation to occur and, after the presentation of the structure and composition of DNA, it was generally accepted, then established, that the genome is what needs to be changed for variation to be produced. At this point, Neo-Darwinism came into play (Same as Darwinism, but stating that DNA is what varies, not mere "traits").
Unfortunately, as the science of microbiology progressed, the statistical impossibilities of mutation as a vector for gradual change and diversification began to present themselves.
- DNA is a code - random mutations convert sense to missense, gradually degrading the code to non-function as more mutations occur in the same gene
- The likelihood of randomly generating not just a random chain of A, C, T, and G, but one which successfully coded for a protein is astronomical
- Proteins exist in three tiers of structure (Amino acids, Aplha helices and Beta sheets, 3D structure and folding), each of which affects the subsequent tier
- Misfolded proteins (3rd tier) are hyper-specific, preventing much toleration for mutation
All of these discoveries create a larger, more impassable gulf for transitional evolution, as present proteins must descend into nonfunction before arriving at a new, functional form, making those intermediates unfavourable forms and unlikely to be selected. After all, we must remember that natural selection selects for the present. It is not some intelligent force that is able to select for future forms. Dr. Michael Behe likened Darwinian evolution to a series of multi-doored rooms in which one cannot backtrack - an individual does not know where each series of choices eventually leads, but, upon reaching a dead end, there is nowhere further to go.
So, I say Darwinism and, by extension, Neo-Darwinism is flailing. Having little solid foundation which is not rendered null by improbability, conflicting theories, or missing evidence, it is built largely upon conviction, a conviction which has defied logical opposition and rational thinking out of a willful desire for its veracity.
It is, in the truest sense of Coleridge's genius, a suspension of disbelief.
Credit must be given to Drs Steven Meyer and Michael Behe as much of what is presented was drawn from a collection of my overall undergraduate education and their books Darwin's Doubt (Meyer), Darwin's Black Box, and The Edge of Evolution (both Behe).