Tuesday 1st May, 2007

 

A New Perspective on Evolution

 
 
 
 
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By B.E. Bishop

Did Charles Darwin get it wrong? Is it the less fit organisms, not the fittest, that evolve? If so, the implications are, of course, momentous.

In 1996, Journal of Heredity published my article entitled Mendel’s Opposition to Evolution and to Darwin, in which I argued that Gregor Mendel, far from being an evolutionist, as is generally assumed, was, in fact, a supporter of the doctrine of special creation, the prevailing belief at the time; that his paper on garden pea (Pisum sativum), which appeared in 1866, was specifically written in controversion of Charles Darwin’s iconoclastic book On the Origin of Species by Means of Natural Selection, published in 1859; and that Mendel’s and Darwin’s theories are completely antithetical. However, once the Mendelian myth has been discredited, it becomes necessary also to re-evaluate Darwin’s contribution to evolutionary biology, for it was only the unification of Darwin’s and Mendel’s ideas in the 1930s and ‘40s, in what is known as the modern synthesis or neo-Darwinism, that was seen to legitimate Darwin’s externalist account of evolution.

But biology has moved on since those days, when genes were not considered to be capable of exhibiting any behaviour other than a tendency to occasionally mutate. Then, perhaps, it was feasible to encapsulate evolution as the natural selection of alternative alleles, or, as it is usually put, a change in gene frequencies. Now, however, it is known that the genome is extraordinarily fluid, with all sorts of internal dynamics of its own, which surely must affect evolutionary directionality. Thus, Darwin should be judged not in the context of the simplistic and fallacious "bean-bag genetics" that were claimed to have substantiated his theory but in relation to all the highly complex and incontrovertible molecular phenomena that have been elucidated since the formulation of the synthetic theory.

Today, it is often asserted or implied that Charles Darwin was the first to suggest that evolution has occurred, but that is not so: he had several precursors, whom he acknowledged in the historical sketch that was added to the third edition of The Origin (1861) and to all subsequent editions. Therefore, Darwin’s originality rests largely upon the validity of his mechanism of evolution, natural selection, which is now regarded by the vast majority of biologists as irrefutable. However, it should not be forgotten that natural selection had remained very much a minority view from the time it was postulated until the advent of neo-Darwinism, having been strongly resisted during that entire period of nearly eighty years, as Ernst Mayr himself, who was the last surviving architect of the modern synthesis, reiterated throughout his book What Makes Biology Unique? Not even Darwin’s contemporaries, friends and foes alike, had been able to accept natural selection as a creative principle, for Darwin’s theory not only aroused fierce religious and philosophical antagonism, as is well known, but was also met with very serious scientific objections, a fact that is little appreciated.

Critics argued (as do many people still today) that natural selection could act only as a negative force, eliminating abnormal variants and preserving the type, while some other cause must play the positive role of orchestrating evolutionary change. In other words, although natural selection could account for the success of species after they have arisen, it could not explain their origin; hence, Darwin’s theory was unproved and the title of his book a misnomer. Furthermore, Darwin’s mechanism of natural selection was based upon an analogy with artificial selection, a comparison that was thought by his peers to be completely inappropriate, for not only does speciation not occur under domestication but the plants and animals chosen for propagation are precisely those that would not survive in the wild, as the characters that are useful to breeders would be deleterious to organisms in a feral state. In fact, everyone who had invoked artificial selection before The Origin (including Charles Lyell, Darwin’s mentor) had done so in order to disprove evolution!

In the face of such an unfavourable response, Darwin began to backtrack, drastically revising later editions of The Origin and admitting in The Descent of Man (1871) that in the earlier editions he had probably attributed too much to the action of natural selection. Darwin also introduced Herbert Spencer’s expression "the survival of the fittest" as a synonym for natural selection in an attempt to counter charges of anthropomorphism, for opponents said that it was obvious that nature’s selection required as much thought and control as man’s selection.

Darwin maintained that small heritable variations occur among populations of plants and animals but that they are not directed towards an organism’s needs (or, as it is put today, that mutation is random, not adaptive); that natural selection, or the survival of the fittest, determines which variants predominate in any particular environment; and that it is the most successful members of a population that over time, after many generations, give rise to a new species, while those lineages that have been outcompeted are driven to extinction.

However, it is possible that Darwin got it wrong and that it is the less fit organisms, not the fittest, that evolve. This is suggested by John T. Bonner’s concept of "pioneering", which holds that the basis of speciation is escape from competition and predation, not only by flight to new habitats but also by the adoption of novel strategies for survival that go right back to the first bacteria and their struggle for a source of energy. Bonner also argues that another option for pioneers is to become too large and complex to be subdued, for the ecological niche that could be occupied by organisms that were larger and more complex than any other organisms existing at the time was always vacant.

Although Bonner sees his ideas as compatible with Darwinian theory, pioneering is obviously a desperate do-or-die effort of the less fit that enables them to survive in the only possible way they can at that particular point in time. Moreover, pioneering incurs considerable costs, for it drives species to seek refuge in inhospitable environments, such as the polar regions or the great depths of the sea, as well as to explore the extremes of complexity. In contrast, successful organisms don’t need to change their lifestyle: they go on being themselves in the same old way, in the same old habitat.

Significantly, more and more pioneering-type scenarios are being put forward these days, even for such major transitions as the origin of multicellularity and of the first tetrapods. However, if it is the inferior and not the superior individuals that are evolving, then clearly natural selection can be playing no part in the process as a creative force, in which case variation must arise preferentially in adaptive directions, as was proposed by Jean-Baptiste de Lamarck, the French naturalist who was the first to formulate a consistent and comprehensive theory of evolution.

Most people think that the main difference between Lamarck and Darwin was the inheritance of acquired characters: that the tenet was propounded by Lamarck and that Darwin rejected it. But that is wrong. The inheritance of acquired characters was not original to Lamarck, nor did he claim it to be; it was the conventional wisdom of his time, as it still was in Darwin’s, and Darwin was a firm believer in the notion.

The most fundamental difference between Lamarck and Darwin was their attitude pertaining to the production of variation: Lamarck held that variation is adaptive, Darwin that it is not directed towards an organism’s needs. And this issue is still the crux of evolutionary theory today, for adaptive variation renders untenable Darwin’s cardinal postulate that natural selection is a creative mechanism.

Please send correspondence to:
B.E. Bishop
6 Barbados Road
Federation Park
Trinidad
West Indies

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