Darwin and the Origin of Species

Ralph E. Taggart, Professor

Department of Plant Biology

Department of Geological Sciences

Michigan State University

After the Beagle

Darwin was quite busy following the end of the Beagle voyage. He began work on what was to be his first book, the Voyage of the Beagle, which would prove to be a best seller and enhance his already growing reputation. The elder Darwin, impressed by his son's success as a naturalist, agreed to support him in that endeavor. Darwin also began work on a historic series of notebooks on what he would call "the species problem". He married his cousin Emma and retired to a comfortable country house in Kent where he began his serious work. From the time of his return, Darwin suffered from a variety of health problems. None were life-threatening, but they were debilitating at times and the result was that he worked in seclusion, avoiding the bustle of the London scientific scene. His correspondence was immense and he was quite pleased to entertain visitors, but he avoided more public occasions whenever possible.

One of the major pieces of work he began was to result, after many years, in his great monograph on barnacles. This was a difficult problem, involving careful taxonomic treatment of a difficult group of organisms, but Darwin reasoned properly that he must achieve success in a major taxonomic problem if he were to have real credibility in dealing with the "species problem". While the barnacle work took a great deal of his time, he also worked diligently on his species notebooks.

Domestication

Darwin reasoned that the somewhat simpler problem of the origin of domesticated plants and animals might have some bearing on how new species might appear in nature. In a relatively short time, he reasoned that they key to the origin of all the various domesticated organisms was the action of humans in selecting traits to be reinforced by selective breeding. Populations of both natural species and domesticated organisms are variable and much of this variability appeared to be inherited. If a dairy farmer wished to increase milk production, for example, he would probably choose his most productive cows for breeding stock with the best available bulls. Providing the procedure was diligently followed, and animals were not permitted to breed at random, the result should be a steady increase in milk production by the progeny of succeeding generations. See later pages on modes of selection for a more complete explanation. In fact, just such increases could be documented from long-term production records in British agriculture and such advances could be seen in all animals and crops of agricultural value, not to mention increases in the quality of other breeds such as dogs, etc. Darwin carefully built a case that demonstrated that all domesticated breeds and varieties had their origin in a similar fashion.

Thomas Robert Malthus - the Idea of Competition

Darwin knew that a natural population has similar inherited variability and that the size of natural populations tended to remain constant, despite a tremendous potential for reproduction. It was clear that if there were the potential for a natural selection that would parallel the conscious selection of the plant or animal breeder, a mechanism would have been found for the origin of new varieties in nature.

A critical point in Darwin's thinking came when he considered a most-unlikely piece of reading for a natural historian - the Essay on the Principle of Population, by Thomas Robert Malthus (1798). Malthus was essentially an economist who wrote his essay considerably prior to Darwin's work. Malthus was analyzing the relationship between human population size and the availability of resources such as food. The key element in Malthus' discussion was that these two factors - population size and resource availability - could never remain in proportion to one another. Increasing population size, as Malthus reasoned, was a geometric function, but, in his view, new resources could, at best, be increased at an arithmetic rate. Inevitably, increasing population size would lead to limits in available resources, causing human populations to compete for those resources that were available. As the gap between populations and resource availability widened, this competition would become more intense, leading ultimately to war and famine.

The concept of competition for resources was, in Malthus' essay, an economic concept, but Darwin realized that it could apply to organisms as well. Biological competition could result in organisms that were best able to compete, by virtue of their adaptations, surviving, breeding, and passing those competitive/survival traits to future generations. Organisms that failed to compete, either in absolute or relative terms, would be less successful in breeding (or might not survive to breed) and thus their traits would become less common in future populations. In essence, Darwin viewed biological competition as the agent of natural selection - the driving force that could change the nature of a species! It is interesting that Malthus' essay would have precisely the same impact on the later thinking of Alfred Russell Wallace (see below).

Why so long?

The key elements in Darwin's concept of Natural Selection were developed in a relatively short time, yet he continues to work steadily on the question for almost 20 years, sharing his thoughts only with his closest scientific colleagues. The cardboard histories of Darwin embodied in textbook accounts stress the care that he put into his work, and that cannot be denied. He was meticulous, but he also chose to focus not on data that would support his ideas, but on examples drawn from nature where natural selection did not seem to be occurring. In each of these seemingly contradictory cases, once the problem had been studied in sufficient detail, he was able to satisfy himself (and later, others) that natural selection was operating in each instance!

Darwin's reluctance to "go public" with his ideas was due, at least in part, to another issue that can be traced through his notebooks - materialism. The upper classes in Britain in Darwin's time put great stock in the moral and social virtues inherent in religion. Remember that Darwin himself had been a theology student and his wife was a devoted Christian. Darwin was quite aware that his ideas posed a solid, scientifically based alternative to the creation accounts embodied in the Old Testament Book of Genesis. What Darwin was proposing was history of life shaped, not by direct, Divine intervention, but by the interactions of species with their environment. Darwin's theories provided a material rather than supernatural explanation for biological diversity. To be labeled a materialist, in Darwin's class and time, a vile epithet indeed. There can be little doubt that his aversion to such a label played a part in his putting off the public unveiling of his ideas.

Darwin and Wallace

Alfred Russell Wallace. Starr and Taggart, 1989, Biology - the Unity and Diversity of Life.

Most textbooks provide the basics of the intellectual encounter that propelled Darwin to eventual publication:

Wallace's independent recognition of the action of natural selection
His sending of a short manuscript on the subject to Darwin
Despite the fact that Wallace's paper dealt with his cherished theory, the fact that he forwarded the manuscript to his friends in the London with a recommendation that it be published.
The fact that these same friends, knowing of Darwin's work over so many years, artfully set up the presentation of papers by each man in a joint session in 1858.
Darwin's publication of his Origin of Species in 1859.

Both men are correctly considered to be co-discoverers of the concept of Natural Selection, but Darwin receives the lion's share of the credit in conventional accounts. There are two reasons cited for this - one legitimate and the other spurious. The legitimate reason concerns the many years Darwin labored to meticulously document the theory. The second, and spurious reason, concerns the later personal and professional history of Wallace.

While Darwin went on, in later years, to deal with the contentious issue of human evolution, Wallace took the view that, while Natural Selection could account for the evolution of almost everything in the world of life, the human intellect was a product of Divine Creation. This picture of Wallace, "caving in to the Creationists" on this critical question, is widely used to diminish his stature in conventional textbook accounts.

The real reason for Wallace failing to cross the line on the question of human evolution is far more complex but is strictly in accord with the dictates of good science, as unlikely as that may seem. While both Darwin and Wallace were proponents of Natural Selection, they differed in a critical way:

Wallace was a "strict selectionist" in that he felt that evolution was driven entirely by Natural Selection.
In contrast, Darwin was a proponent of the view that selection could operate along with other factors to drive the evolutionary process.

This difference in view turned out to be critical. Try as he might, Wallace could not construct a mechanism by which the major gap in intellect between humans and other animals could be explained on the basis of selection. If intellect was not the product of selection, given the nature of Wallace's views on the primacy of the selection process, the only alternative was that it must have arisen as a direct result of God, acting to differentiate us from the creatures around us. In effect, Wallace was attempting to be true to the implications of his own strict views on the role of selection and he has not been well-treated by authors who fail to grasp the intellectual issues at the core of this particular debate. There can be no doubt that the human intellect is the result of biological evolution, but the precise mechanism by which it reached its present state is far more complex that either Wallace or Darwin could know, and it has yet to be sorted out in its entirety.

Ralph E. Taggart (taggart@msu.edu)