May 12, 2009
Skyhooks and cranes-8: Alternatives to natural selection
(For other posts in this series, see here.)
In the half century after Charles Darwin published his On the Origin of Species in 1859, the idea of evolution gained considerable ground but the theory of natural selection was just one of several mechanisms that drove the process, and hence the anti-religious implications of the theory were somewhat muted.
Some of these alternative theories were modified forms of Lamarckism, the idea that characteristics that an organism acquired during its lifetime that enabled it to survive better were somehow transmitted to the entities in the body that carried inherited traits to their progeny, so that children inherited that acquired trait. These changes could either come about because of animals needing or desiring a change (the famous Lamarckian example of giraffes getting longer and longer necks as a result of having to strain to reach high leaves) or the 'use-disuse' theory, that body features that people used a lot would grow and become more common while those that they did not need or use would atrophy and disappear (the example here being the building of certain muscles in the body or the disappearance of fish-like features once they became land animals).
The difference between use-disuse theory and natural selection is subtle but important. In use-disuse theory, if an organism does not use some property, that property gets diminished in its offspring. So a parent who does not exercise is more likely to have children who are not athletic, because the parent did not exercise. In natural selection, on the other hand, it is the variations in genes that result in variations in the properties of organisms and those organisms that have features that provide a selection advantage are more likely to survive to adulthood and to parent offspring. Hence those genes tend to increase in the population. So whether a child has good eyesight or not depends (at least to some extent) on the parents' genes and not on the parents' lifestyle, except insofar as the parents' lifestyle influences the child's lifestyle.
Another alternative to natural selection was the theory of orthogenesis, that suggested that evolution followed a path determined by forces originating within the organisms themselves. This made it possible to think that the laws of evolution contained within them forces that guaranteed the eventual emergence of the human species.
The alternative theories such as use-disuse and orthogenesis had the reassuring feature that there was some sort of deliberate and directed progression in evolution, enabling their believers to still think of human beings as special and as the pre-ordained end point of the process. The idea that human beings were special in the eyes of god could thus be retained, giving religious believers the comfort that their lives had the external meaning that they sought.
The theory of evolution by natural selection offered no such assurances. But in the second half of the 19th century, even after the publication of Darwin's famous book On the Origin of Species in 1859, this disturbing idea was in the background. In fact, by the end of the 19th century, the theory of natural selection (though not evolution as a whole) seemed to be in full retreat.
The year 1900 saw the rediscovery of Gregor Mendel's 1865 work on genetics. We now realize that this discovery removed one of the major objections to the acceptance of the theory of natural selection, which was the idea that children were thought to have the average properties of their two parents, so that even if one organism developed a favorable feature, that feature would become diluted in the next generation because that organism would most likely mate with another organism that did not have the favorable feature. There did not seem to be a good way for a positive feature to steadily increase from generation to generation in small incremental steps, the way that natural selection postulated. Mendel's theory allowed changes to remain in the population without getting diluted by mating.
But the implications of Mendel's work were initially misunderstood and theory was thought to work against Darwinian natural selection, further hastening its decline in importance. As a result of all these factors, the idea of natural selection as the fundamental mechanism for the evolutionary process went into an even greater period of decline that continued into the early years of the 20th century, even as the fact of evolution was increasingly accepted. (Peter J. Bowler, The Eclipse of Darwinism, 1983)
But beginning around 1910, the emergence of the new field of population genetics that correctly coupled Darwinian natural selection with Mendelian genetics, created what is now called the neo-Darwinian synthesis. The mathematical analyses of scientists such as J. B. S. Haldane, Sewall Wright, and R. A. Fisher put natural selection on a solid theoretical footing and led to the resurgence of that idea as the prime mechanism for evolution. By around 1920, the reversal was complete. Darwin's theory of natural selection was ascendant and has remained so ever since, growing even stronger with time. (William B. Provine, The Origins of Theoretical Population Genetics, 2001).
But one consequence of this dominance was that the idea that human beings were somehow designed by god, and that the process of evolution was somehow guided to eventually produce them, was seen as incompatible with science. The idea that humans had a special purpose was no longer seen as credible.
Meanwhile, we saw that up through the end of the 19th century, there had been a consensus that it was good to keep religion and the state separate, and the use of religious teaching and prayers and the Bible in public schools had been steadily declining. But around the turn of the century, there were increased rumblings that perhaps this had been carried too far and efforts were made to restore the balance. And the start of the 20th century saw the beginnings of a push to bring back the Bible and religion into public schools.
This renewed interest in putting religion back in schools happened to coincide with the resurgence of natural selection and is, I believe, the reason that the US has had this seemingly unique obsession with, and hostility towards, the theory of evolution by natural selection.
Next: The resurgence of natural selection and the resurgence of religion.
POST SCRIPT: Faulkner
Some time ago, I expressed my sense of frustration with the literary output of writers like James Joyce and William Faulkner for seemingly going out of their way to make their works difficult. The comic strip Pearls Before Swine seems to take a similarly dim view.