Evolution by Mixing and Matching

Skeletons of the early horse-relative Eohippus (left) and modern Equus (right). From Animals of the Past by Lucas.

During the early 20th century many biologists were considering a variety of mechanisms other than natural selection as the primary cause of evolutionary change. The trouble was that many of those researchers were often vague when it came to the details of how such alternative processes might work. Such was the case with paleontologist Frederic Augustus Lucas, who apparently preferred to think of evolution as variations stimulated by the environment building upon themselves over time.

I found this to be rather baffling. The process Lucas presented sounded similar to natural selection but clearly was not the same, and he did not provide enough detail to fully comprehend his meaning. Yet a later book written by Lucas provides an important clue. In the 1922 edition of his book Animals of the Past Lucas repeated what he had previously said and attributed his view of life to a "Professor Cook." This led me to a 1908 paper, "Methods and Causes of Evolution", written by Orator Fuller Cook and published by the United States Department of Agriculture.

In the preface to the paper Chief of the Plant Bureau B.T. Galloway and Secretary of Agriculture James Wilson affirmed that understanding evolution was essential to solving problems of "breeding and acclimatization" in crops. Degeneracy had to be avoided at all costs, yet there was no general agreement on what might be pushing evolution forward. That natural selection was capable was doing so was severely in doubt, as seen in a quote by Alexander Graham Bell's at the end of the introductory letter;

I, too, entertain the feeling that natural selection does not, and can not, produce new species or varieties, or cause modifications of living organisms to come into existence. On the contrary, its sole function is to prevent evolution. In its action it is destructive merely, not constructive–causing death and extinction, not life and progression. Death can not produce life; and though natural selection may cause the death of the unfit, it can not produce the fit–far leas evolve the fittest. It may permit the fit to survive by not killing them off if they are already in existence; but it does not bring them into existence or cause improvement in them after they have once appeared. We must look to other agencies for the causes of evolution. A closed gate may block a road, but it does not push the traveler into a new path, or. indeed, cause him to move at all. It is a mere static obstruction, not a dynamic force. In a similar manner natural selection prevents evolution along certain lines; but it is not a dynamic force compelling progress along other lines. The motive power of evolution must be sought elsewhere.

Natural selection had run into this objection for years. Perhaps it had the power to preserve what had been evolved or could weed out the "less fit", critics argued, but it was often seen as a destructive force rather than a creative one. In this Cook agreed, characterizing the evolutionary mechanism Charles Darwin and Alfred Russell Wallace proposed in the following manner;

Natural selection and other agencies of the environment have not been found to cause the evolution of species. After fifty years of study of evolution it is becoming apparent that constructive evolutionary changes are spontaneously put forth by species, which tend to these evolutionary motions as naturally as inanimate objects tend to remain at rest. ... The theory that selection causes evolution, notwithstanding its wide popularity, seems not to be well founded. It stands in the way of further progress in evolutionary science and interferes with the full development of the art of breeding.

This position may be difficult to understand given our present way of looking at evolution, but Cook did not consider adaptation to local conditions to be an important part of evolution. If this was true, though, how did evolution actually occur? Many naturalists generally agreed on the pattern of evolution, but what about the mechanism which, in Cook's words, "actuate[d] the motion" of change?

In Cook's estimation there was something inherent in species that caused them to evolve. Natural selection only tweaked the results. New characteristics did not arise because they were called into being by natural selection but because they evolved on their own first. Eventually creatures possessing more primitive traits would be swept away by natural selection, effectively clearing the field of stragglers. Yet Cook did not present natural selection as a consequence of a set of given conditions (variation, variation conferring survival/reproductive advantages, heritability of variations). For him it seemed to work more like a natural force that was quite different than what Darwin and Wallace had actually proposed.

Cook's strange interpretation of natural selection became apparent in his discussion of "useless" traits. If evolution proceeded by natural selection, Cook argued, there should be no "useless characters" as natural selection would weed those characteristics out; all characteristics would be required to have some use. In Cook's view, then, natural selection was not about optimization of organisms given contingency and constraints but the absolute perfection of living forms. Any flawed structure could be cited as evidence that natural selection (in Cook's view) was not driving evolution.

It is important to note, however, that Cook did not favor evolution by means of "saltations" or macromutations, either. This would be the equivalent of a bird being hatched from a reptile's egg, or a similar massive change in single generation. Cook stressed the continuity of life, ancestors had to sensibly link with descendants, and even if saltations occurred they did not necessarily lead to the establishment of new forms.

Likewise, Cook rejected other popular evolutionary mechanisms such as evolution through acquired characteristics (as attributed to Lamarck) and internally-directed evolution (orthogenesis). If the latter mechanism caused evolution, especially, then natural selection would be powerless to cause adaptations, something Cook knew was not true. Despite his protestations in the earlier portions of the paper, Cook did not deny natural selection. Instead he wanted to find what he felt was its proper place. If all these popular mechanisms could be ruled out, however, what was actually causing evolution?

Variation among individuals of a species, or what Cook called "heterism", was essential to his evolutionary hypothesis. The normal distribution of variation in a natural species supplied the different pathways by which organisms could change. Interbreeding of many individuals thus perpetuated some variations and mixed them through a population, with the variations present in the previous generation determining what would appear in the next. Cook did not envision any sort of restrictive breeding or sexual selection; variable members of a species were free to interbreed and spread their variations far and wide.

Cook's vision of evolution is somewhat reminiscent of evolutionary change caused by genetic drift. Individuals in a population vary and reproduce within that population to produce a new distribution of those traits in the next generation. For Cook, it was this sort of shuffling and reshuffling of variations that drove evolutionary change, but in his view any restriction (i.e. selection) placed on reproduction would stifle evolution;

When diversity of descent and broad breeding are recognized as the conditions of normal reproduction and evolutionary progress ... the meaning of the law against perpetual narrow breeding [restrictive reproductive selection] becomes plain. ... Broad networks of descent are necessary to maintain efficiency of reproduction and organic vigor in the species. To destroy the network of descent removes the support of the organic structure.

A few lines down, Cook more explicitly explains how his version of evolution might work;

The facts are concrete and their relations obvious. The members of each species are diverse (heterism). They freely interbreed among themselves (symbasis). They produce successive generations (descent) . Later generations differ from the earlier (evolution). Without diversity, interbreeding has no significance, and descent is not accompanied by evolution. Heterism, symbasis, descent, and evolution form a continuous series, a complete chain of phenomena. For some purposes the four processes may be described as distinct, but physiologically they are mere phases or aspects of organic existence, each at once requiring and assisting the others.

Cook later reinforces this by considering how this process might shape evolutionary history;

Evolution is analogous to history. The importance of events is determined by the conditions and the sequences in which they occur. Species are not carried along by their environments, nor compelled by internal clockworks to change at particular times or to go in definite directions. Nevertheless, the timely putting forth of a new character may have a profound influence upon the subsequent history of a species. Variation is genetic, for species tend to evolve, but it is not definitely directed or determined (orthogenetic). A character once formed tends to further development, and thus finds the range of greatest utility or of most harmonious combination.

For Cook, then, evolution was driven entirely by the capacity for creatures to vary. Natural selection was a real phenomena but had no effect in shaping life. Instead evolution was a kind of lottery where any creature able to mate was eligible to enter. Such a system, in Cook's view, would allow evolution to proceed without any breaks in continuity. It would result in the same pattern of life's history that Darwin saw, just by a different means.

I must admit that I did not expect to find such a unique view in Cook's report. I do not recall ever stumbling across anything else like it from that time period. Novelty does not translate to accuracy, of course, and Cook's views on the primary mechanism of evolution are a bit muddled and fall apart when held up to the evidence we presently possess, but they are still very interesting when considered in a historical context. (I was especially intrigued by Cook's notion of variations spreading through a interbreeding members of a species.) It was one of many ideas competing in the intellectual "struggle for existence" over the causes of evolution at the time, and like many others it slipped away into a kind of extinction.