How has evolution successfully produced the diversity of organisms occupying virtually every ecological niche on the planet? This has been the central question in scientific evolution since thinkers in the late 18th century (including Erasmus Darwin, Charles' grandfather) introduced the idea that living organisms change over time. The big unknowns were how heredity worked, how change occurred, and how hereditary variation (called "descent with modification") transformed itself into useful biological diversity.
The Wallace-Darwin theory of "survival of the fittest" published in 1858 was the first plausible scheme for converting variation into adaptive differences. Although unable to say anything significant about the nature of hereditary transmission or variation, they proposed the following idea. Variants fittest (best able) to survive the Malthusian struggle for existence and reproduction in a world of limited resources would progressively become different and dominant. Eventually, differences would accumulate to the point that new species would form.
Darwin's 1859 Origin of Species had tremendous impact for two reasons. First, it made plausible the notion of change through differential reproduction available to the general reader. Finally, the public saw there was a scientific alternative to supernatural creation.
Second, Darwin providentially gave the name "Natural Selection" to the process ensuring "Preservation of Favoured Races in the Struggle for Life," as he subtitled his book. Proponents of evolution had a concise phrase to use when asked to explain how this new natural source of biological transformation actually worked. The satisfaction of having a short answer to a difficult question proved irresistible then, as it does today.
Did Wallace and Darwin hit the nail on the head and identify the crucial process of biological diversification? To most people, and especially to the evolutionist profession, the answer is so obviously "Yes" that even to pose the question subjects the person asking to abuse. My readers can see that from some of the comments on this blog.
Nonetheless, all questions are permissible in science. This one about evolution is particularly important. Either evolution is an exciting subject able to incorporate diverse approaches, or it is a closed subject basically solved 150 years ago, when we knew virtually nothing about heredity or hereditary variation.
Because of the public conflict between religious fundamentalism and scientific positivism (the notion that science has all the answers), public policy in science education has become linked to my question. If evolutionists are right that all basic questions have been resolved, then the atheist crusade of Dawkins and allies may have a rational basis. However, if the answer to my question is "No," then perhaps we can find a way out of this destructive dialogue of the deaf.
So, let us look more closely at the Darwinist position on evolution. Does selection for reproductive fitness lead to creative changes? Wallace once argued the reverse. He viewed selection as a stabilizing feedback mechanism, like a steam engine "governor," keeping organism features constant as long as the environment remained the same.
Darwin modeled natural selection on artificial selection by humans. He ignored the inconvenient fact that human selection for altered traits has never generated a truly new organismal feature (e.g., a limb or an organ) or formed a new species. Selection only modifies existing characters. When humans wish to create new species, they use other means.
In hailing natural selection as a blind creative force, Darwinists ignore the irony that Darwin's model of human selection is an intentional, goal-directed process with a desired outcome. It is precisely the opposite of a blind force.
Darwin was correct in believing that natural selection could only play a creative role if variation was continual and small. Based on the "Uniformitarian" idea that change had to occur in the small steps we observe under normal conditions, he originally insisted that evolutionary innovation had to be gradual. "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case" (Origin of Species, Chapter 6).
Unlike most followers, Darwin acknowledged later that significant, sudden changes could occur in a fundamentally different way. He wrote about "... variations which seem to us in our ignorance to arise spontaneously. It appears that I formerly underrated the frequency and value of these latter forms of variation, as leading to permanent modifications of structure independently of natural selection" (Origin of Species, 6th edition, Chapter XV, p. 395, emphasis added).
So a way to rephrase my question is to ask: Have we learned since 1859 about processes that can lead to organism change "independently of natural selection?" The answer is overwhelmingly positive.
Two fields principally illuminated the basic mechanisms of heredity and variation:
- cytogenetics (the study of chromosome behavior in heredity using both genetic and microscopic methods) and
- molecular genetics (using DNA analysis to identify the nature of genome change).
In combination, cytogenetics and molecular genetics have taught us about many processes that lead to biological novelties "independently of natural selection" -- hybridization, genome duplication, symbiogenesis, chromosome restructuring, horizontal DNA transfer, mobile genetic elements, epigenetic switches, and natural genetic engineering (the ability of all cells to cut, splice, copy, and modify their DNA in non-random ways). As previous blogs document and as future blogs will discuss, the genome sequence record tells us that these processes have accompanied rapid changes in all kinds of organisms. We know that many of them are activated by stress under extraordinary circumstances.
Fortunately for evolution science and science education, 20th century studies of inheritance at the cellular and molecular level have freed us from the intellectual straightjacket of gradual random change and natural selection. In the 21st century, we can think open-mindedly about the cellular and molecular processes that lead to biological diversity. Today, we can investigate how they work to achieve evolutionary success, particularly in crisis situations, when novelty is most necessary.