This post is a follow-up to Understanding Talmage, Widtsoe, et al.
Through his publication of The Origin of Species, Charles Darwin established that evolution occurred and argued that natural selection was the chief process of evolution. By 1870 most biologists were convinced that evolution occurred, however there was a lot of doubt about natural selection, which would not be re-established as the dominant force of evolution until the modern synthesis of the 1930's and 40's. The intervening time has been called "the eclipse of Darwinism." (Note that the term Darwinism has had several different meanings through history. This post uses the term with reference to evolution with an emphasis on natural selection.) There were several reasons for this eclipse, not the least of which was that many people thought natural selection was too materialistic.
The main historical rivals of natural selection follow below. (For convenience, unless otherwise noted, quotes are from wikipedia.)
1. Orthogenesis: "the hypothesis that life has an innate tendency to move in a unilinear fashion due to some internal or external 'driving force'." In other words, evolution moved along predetermined trends. Orthogenesis was popular with some paleontologists, who saw trends in the fossil record (e.g. horses) which were interpreted in a straightforward manner of A -> B -> C. This theory collapsed because no mechanism could be found to drive such trends, and the very existence of the trends was undermined by a more complete fossil record, which showed multiple branching lineages that lacked an overall directed trend.
2. Neo-Lamarkism: "Lamarckian evolution refers to the once widely accepted idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring." This idea was easily hitched to the notion of progress--that species could improve themselves through behavior. However, experimental support was lacking, and with the rise of genetics it became apparent that there was no way for acquired characteristics to be transmitted to the genome.
3. Mutationism: Historically, the word "mutation" has been used differently than our current scientific use (a change in genotype). In the early years of genetics the word was associated with saltations, or jumps. Genetic traits were often discontinuous (think of the simple either/or traits that Gregor Mendel studied), and it was thought that new species arose through sudden saltations. For decades mutations were seen as the chief alternative to natural selection (orthogenesis and neo-lamarkism having been refuted, in part, by genetics). However, as understanding of the complex interactions between genes grew, it seemed increasingly unlikely that radical changes could result in surviving organisms, and the many failures that would be expected were missing. The modern synthesis finally brought the two concepts together with mutations providing the variation upon which natural selection acts (so to speak). All of this preceded the elucidation of molecular genetics (i.e. determination of the structure of DNA, how it codes for proteins, etc).
It is also important to consider the Great Chain of Being, or scala naturae. We intuitively see that life-forms vary in complexity and intelligence, and the chain of being was a medieval concept that organized life on earth into an ascending ladder-like hierarchy that culminated with humans at the top. According to Bowler (p. 63) [1],The attractions of the chain of being came not from its practical applications but from its articulation of certain key assumptions. It was conceived as a static plan of nature: all the links in the chain were created together by God. It was a highly structured system in which every species had an unambiguous position, with its closest relatives placed one above and one below it in the sequence. It was a complete system: every link in the chain from amoeba to human, had to exist, and God's perfection was displayed by the fact that He had created every link in the chain...
The alternatives to natural selection listed above were sometimes linked (at least implicitly) to the hierarchal chain of being, thus giving a sense of progress through time as organisms climbed the ladder. In addition, the historical evolution of life was sometimes likened to the development of a fetus (in fact there are evidences for evolution in fetal development), which at the very least gave a sense of progress and goal-oriented development. However, these notions of evolutionary progress rely on human values and subjective judgments rather than objective criteria or mechanistic laws, and there is no evidence that mutations occur in anticipation of the future.
In summary, much of LDS commentary on evolution by General Authorities or other prominent members occurred before the evolutionary synthesis, and although some argue that current biology has outgrown that synthesis (e.g. here), the ideas that flourished during the eclipse of Darwinism have not been vindicated in any significant degree. This history of science should be kept in mind when reading such commentary.
References:
It is difficult enough to keep up with current science without trying to understand science of the past. I primarily consulted the following references in drafting this post.
1. Bowler, Peter J. Evolution: The History of An Idea.
2. Mayr, Ernst. What Evolution Is.
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