With a growing number of distinguished evolutionists - including Ernst Mayr, Edward O. Wilson, and Francisco Ayala - I believe that Darwinism is more than just a scientific theory. It is the basis for a full world view, a Weltanschauung.
Michael Ruse (1986), p. 513
NATURAL SELECTION: A DEFINITION
A typical definition of the term "natural selection" reads as follows (Parker, 1997, p. 312): "Darwins theory of evolution, according to which organisms tend to produce progeny far above the means of subsistence; in the struggle for existence that ensues, only those progeny with favorable variations survive; the favorable variations accumulate through subsequent generations, and descendants diverge from their ancestors." A definition concentrating on evolution by "differential survival and reproduction of the members of a population" (Catania, 1994) deviates in an important point from that just given. The progeny which differentially survives is not necessarily the fittest, a point best illustrated by island populations endangered by more or less closely related intruders worldwide.
AREA OF APPLICATION: STRONGLY DIFFERENT OPINIONS AMONG SCIENTISTS
Apart from a few exceptions (Lima-de-Faria, 1988; Chauvin, 1997), most contemporary biologists and other scholars accept natural selection as a real process in nature. However, as to the extent of the effects of natural selection on the differentiation and the origin of new species and higher systematic categories, the differences of opinion are enormous; see, for example, Bell (1997), Catania (1994), Cziko (1995), Dawkins (1986, 1995, 1987/1996, 1998), Dennett (1995), Mayr (1997, 1998), Ruse (1996), versus Behe (1996), Berlinski (1996), Dembski (1998a), Junker and Scherer (1998), Lönnig and Saedler (1997), ReMine (1993), and Schützenberger (1996). The first group of authors firmly believes that natural selection is the key process for the origin of all life forms on earth, whereas most scientists of the second group are entirely convinced that the action of natural selection is only of limited significance and that it is largely incompetent to explain the origin of lifes major features from biochemistry to systematics, especially the origin of higher systematic categories. Both groups claim that scientific reasons are the basis of their position in biology. Missing links representing nearly all possible shades between the views of these two groups may also be found; see, for instance, Chandebois (1993), Denton (1985, 1998), Gould (1996, 1997), Ho and Saunders (1984), Kauffman (1993), Prothero (1998), and Stanley (1998).
SOME BASIC PROBLEMS
The Reproductive Powers of Living Beings and the Survival of the Fittest
Dobzhanskys 1937 work Genetics and the Origin of Species is generally viewed as the crystallization point for the origin and growth of the modern synthesis or neo-Darwinian theory of evolution (Lönnig, 1999a). There is hardly a better example to illustrate the key message (and, at the same time, the weaknesses) of the modern theory of natural selection than the following quotation from this pioneering work of Dobzhansky (p. 149):
With consummate mastery Darwin shows natural selection to be a direct consequence of the appallingly great reproductive powers of living beings. A single individual of the fungus Lycoperdon bovista produces 7 x 1011 spores; Sisymbrium sophia and Nicotiana tabacum, respectively, 730,000 and 360,000 seed; salmon, 28,000,000 eggs per season; and the American oyster up to 114,000,000 eggs in a single spawning. Even the slowest breeding forms produce more offspring than can survive if the population is to remain numerically stationary. Death and destruction of a majority of the individuals produced undoubtedly takes place. If, then, the population is composed of a mixture of hereditary types, some of which are more and others less well adapted to the environment, a greater proportion of the former than of the latter would be expected to survive. In modern language this means that, among the survivors, a greater frequency of carriers of certain genes or chromosome structures would be present than among the ancestors...
For agreement on and further documentation of the principle of natural selection, see the group of authors cited above, beginning with Bell (1997). However, in the 1950s, French biologists, such as Cuénot, Tétry, and Chauvin, who did not follow the modern synthesis, raised the following objection to this kind of reasoning (according to Litynski, 1961, p. 63):
Out of 120,000 fertilized eggs of the green frog only two individuals survive. Are we to conclude that these two frogs out of 120,000 were selected by nature because they were the fittest ones; or rather - as Cuenot said - that natural selection is nothing but blind mortality which selects nothing at all?
Similar questions may be raised for the 700 billion spores of Lycoperdon, the 114 million eggs multiplied with the number of spawning seasons of the American oyster, for the 28 million eggs of salmon and so on. King Solomon wrote around 1000 BC: "I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong,...but time and chance happeneth to all of them" (KJV 1611).
If only a few out of millions and even billions of individuals are to survive and reproduce, then there is some difficulty believing that it should really be the fittest who would do so. Strongly different abilities and varying environmental conditions can turn up during different phases of ontogenesis. Hiding places of predator and prey, the distances between them, local differences of biotopes and geographical circumstances, weather conditions and microclimates all belong to the repertoire of infinitely varying parameters. Coincidences, accidents, and chance occurrences are strongly significant in the lives of all individuals and species. Moreover, the effects of modifications, which are nonheritable by definition, may be much more powerful than the effects of mutations which have only "slight or even invisible effects on the phenotype" (Mayr 1970, p. 169, similarly 1976/1997; see also Dawkins, 1995, 1998), specifying that kind of mutational effects most strongly favored for natural selection and evolution by the neo-Darwinian school. Confronting the enormous numbers of descendants and the neverending changes of various environmental parameters, it seems to be much more probable that instead of the very rare "fittest" of the mutants or recombinants, the average ones will survive and reproduce.
Natural Selection, Population Genetics, and the Neutral Theory
Despite the impossibility to produce a strictly deterministic model for natural selection in the face of myriad varying parameters, there have been several attempts to quantitatively assess this problem. Fisher, perhaps the most important forerunner of the neo-Darwinian theory, has calculated (1930) that new alleles with even 1% selective advantage (i.e., more than is usually expected by neo-Darwinian theorists), will routinely be lost in natural populations. According to these calculations the likelihood of loosing a new allele with 1% advantage or no advantage is more than 90% in the next 31 generations (Fisher, 1930/1958; Dobzhansky, 1951; Schmidt, 1985; see also ReMine, 1993; Futuyma, 1998; Maynard Smith, 1998). Considering genetic drift, i.e. random fluctuations of gene frequencies in populations, Griffith and colleagues state in agreement with these authors (1999, p. 564):
Even a new mutation that is slightly favorable will usually be lost in the first few generations after it appears in the population, a victim of genetic drift. If a new mutation has a selective advantage of S in the heterozygote in which it appears, then the chance is only 2S that the mutation will ever succeed in taking over the population. So a mutation that is 1 percent better in fitness than the standard allele in the population will be lost 98 percent of the time by genetic drift.
Nevertheless, it appears that if such a mutation occurred at a constant rate in a large population, it would have a fair chance to become established after an average occurrence of about 50 times. However, such estimates are made on exceedingly imperfect assumptions biased in favor of the modern synthesis. Note that the basis of these calculations are dominant mutant alleles with 1% fitness increase in the heterozygous state. In the plant kingdom, however, more than 98% of all the mutations are recessive and more than 99.99% of the dominant (as well as homozygous recessive) mutants in the plant and animal kingdoms are lowering fitness. Modifications, juvenile stages, and the endlessly varying environmental parameters are not (and hardly can be) taken into account, nor is the objection of the French biologists quoted above addressed. Dobzhanskys "death and destruction of a majority of the individuals" occurs mainly before sexual maturity - as can be seen, for instance, each spring when billions of tree-seedlings appear, of which only an extremely low minority will ever become adult or full-grown trees: obviously the environment is far more relevant than a 1% genetic advantage.
Most importantly, the calculations are invalid for small populations where most of the evolutionary novelties are said to have arisen according to the neo-Darwinian theory of evolution and punctuated equilibrium alike (Gould & Eldredge, 1993; Mayr, 1976/1997, 1998; Stanley, 1999). In a small population the rate of advantageous mutations is extremely low (if they appear at all; aeons of time are needed to obtain the average 50 identical advantageous dominant mutations for one success) and genetic drift is almost totally substituting natural selection. Also, it is not possible in nature to raise mutation rates indefinitely since error catastrophe occurs when the mutation rate is too high, thereby terminating the existence of the population.
Neutral, slightly deleterious and moderately favorable alleles all have nearly equal chances to spread in diploid populations - as the neutral theory of population genetics has definitely shown (Kimura, 1983; ReMine, 1993; see already Fisher, 1958). The neutral theory "contends that at the molecular level the majority of evolutionary changes and much of the variability within species are caused neither by positive selection of advantageous alleles nor by balancing selection, but by random genetic drift of mutant alleles that are selectively neutral or nearly so" (Li, 1997, p. 55). Hence, the net result of larger numbers of gene mutations can mean overall degeneration of a species instead of upward evolution. Moreover, the costs of the many substitutions necessary for neo-Darwinian evolution to function successfully in large populations can quickly surpass the adaptive possibilities of a species (see the discussions of Haldanes Dilemma by Dobzhansky et al., 1977; and especially ReMine, 1993.)
Selection and Neutral Structures on the Morphological Level
On the morphological and anatomical level, there are many structures in nature for which no selective advantages can be found. For example, what could be the selective advantage of a plant displaying leaves with entire margins compared to one having dentate leaves or a plant with dentate leaves compared to one with serrate or doubly serrate leaves? A caterpillar would probably be quite happy finding more starting and attachment points for eating such leaves, which could be a decisive selective disadvantage for the plant. Also, many hypertrophic structures have appeared in the history of life (as in the cases of the enormous canine teeth of saber-toothed tigers, the burden of weighty antlers in prehistoric deer) which seem to have led to the extinction of the affected species. Why did natural selection not select genes that would in time diminish such structures? Sexual selection will hardly solve these problems but constitutes a problem of its own (Lönnig, 1993).
DOES NATURAL SELECTION EXIST AT ALL?
The remarks made so far, however, do not refute the occurrence of natural selection. In spite of the problems just mentioned, it is self-evident that physiologically, anatomically, and ethologically damaged mutants and recombinants (to speak again in the contemporary genetic language of these individuals) will be at a disadvantage in many situations (lame prey in relation to their predators and vice versa). It is only on islands with loss or diminution of stabilizing selection that processes of degeneration may occur quickly (for further discussion of the topic, see Lönnig, 1993, 1998; Kunze et al., 1997). Furthermore, survival of the fittest evidently takes place, for example, in cases of alleles and plasmids with strongly selective advantages, as in the cases of multiple resistance in bacteria and resistance to DDT in many insect species. After pointing out that Darwin knew hardly any cases of natural selection, Mayr asserts (1998, p. 191): "Now, there are hundreds, if not thousands, of well-established proofs, including such well-known instances as insecticide resistance of agricultural pests, antibiotic resistance of bacteria, industrial melanism, the attenuation of the myxomatosis virus in Australia, the sickle-cell gene and other blood genes and malaria, to mention only a few spectacular cases."
THE EVOLUTIONARY POTENTIALS AND LIMITS OF NATURAL SELECTION
According to the first group of authors mentioned earlier, there are hardly any evolutionary limits for natural selection. The assertion that "through billions of years of blind mutations pressing against the shifting walls of their environment, microbes finally emerged as men" by H. J. Muller (who was awarded the Nobel prize for his work in mutation genetics) may illustrate this conviction in the near omnipotent potentials of mutation and natural selection. Avise states (1999, p. 83) that "natural selection comes close to omnipotence". The second group of authors, however, point to several investigations which are at odds with this view (see discussion in the next paragraphs).
The Law of Recurrent Variation and Selection Limits
Mutations are thought to be the ultimate basis for evolution by natural selection. So, lets have a look at the question of whether mutations could have provided the raw materials for natural selection for the origin of all species and life forms of the earth. Having investigated the question for about 35 years now including the work with collections of mutants of two model plant species (the pea and the snapdragon - more than 1 million plants), I have come to a conclusion strongly differing from the modern synthesis concerning the potential of mutagenesis. The results I have summed up in "the law of recurrent variation" (Lönnig, 1993, 1995; Kunze et al., 1997). This law specifies that, for any case thoroughly examined (from pea to man), mutants occur in a large, but nevertheless limited spectrum of phenotypes which - in accordance with all the experiences of mutation research of the 20th century taken together - cannot transform the original species into an entirely new one. These results are in agreement with the statements of several renowned evolutionary geneticists, two of whom are quoted here. Hans Stubbe wrote after a lifetime spent in mutation research (1966, p. 154):
The improved knowledge of mutants in Antirrhinum has provided some essential experience. During the years each new large mutation trial showed that the number of really new mutants recognized for the first time, was steadily diminishing, so that the majority of the genetic changes was already known.
And Gottschalk stated in 1994, p. 180, "The larger the mutant collections are, the more difficult it is to extend them by new mutation types. Mutants preferentially arise that already exist."
To understand these observations one must clearly distinguish between two levels: first, the level of the phenotypes, and second, the DNA level. On the latter, the potential of missense and nonsense mutations and other sequence deviations is nearly infinite. However, the spectrum of the resulting different phenotypes is not, because the space of functionally valid sequences within a given system of tightly matching regulatory and target genes and correspondingly co-ordinated functions involved in the formation of the finely balanced whole of an organism, cannot infinitely be stretched by chance mutations.
To take a crude illustration: Drop your computer from the desk or take a screwdriver and a hammer, open the casing, shut your eyes and then forcefully operate in the innards! Depending on the number of computers and how often and for how long one proceeds to act this way, one may collect a nearly endless number of non-functional changes. Yet - with much luck - one may also select a few operationally diminished, but nevertheless still working, systems. Thus, one may demolish a computer in a thousand and more different ways by some accidental procedures. However, the resulting still more or less functional states (the functional phenotypes), will be limited. The hope to secure a Pentium III from a 486er by this method would be very bold indeed. - Of course, the situation in biology is more complex than in engineering, because organisms are, for instance, reactive entities. Nevertheless, limits to selection have repeatedly been found in several areas of biological research.
The limits of selection due to the absence of hoped-for positive mutations were most severely felt in mutation breeding at the end of the 1970s and in the 1980s after some 40 years of worldwide mutation research with cultivated plants as maize, rice, barley, peas, and others. Mutation induction was originally thought to revolutionize plant breeding and substitute the costly and time-consuming "old" recombination method on a global scale. By mutation genetics, three time-lapse methods were available to the breeders: (a) raising the numbers of mutations so enormously in a few years, that nature would have needed millions of years to produce similar amounts of hereditary changes; (b) well-aimed and careful selection and conservation of promising genotypes, which often would have been lost in nature; and (c) well-aimed recombination of rare genotypes for which the chance to ever meet and mate in nature would again be very small.
After the neo-Darwinian school of biologists had taught plant breeders that mutation, recombination, and natural selection were responsible for the origination of all life forms and structures on earth, the possibility of the threefold time-lapse-method led to a previously unknown euphoria among geneticists in order to revolutionize plant breeding. Literally billions of mutations were induced by different mutagenic agents in many plant species. However, relatively few useful mutants were obtained, mostly loss-of-function-mutants loosing undesirable features like toxic constituents, shattering of fruits, spininess and so on. Due to the limits summarized by the law of recurrent variation (also pertinent to the processes in nature, i.e. for natural selection), these efforts ended in a worldwide collapse of mutation breeding some forty years later. It is self-evident that selection, whether artificial or natural, cannot select structures and capabilities which were hoped or believed to arise, but never did (Lönnig, 1993, 1998). Thus, qualitative limits in generating positive mutations point to the limits of natural selection.
Selection Limits in Population Genetics and their Relevance for Natural Selection
The situation in population genetics, where selection limits have been found and described in many papers, has been summarized by Hartl and Jones as follows (1998, p. 686):
Population improvement by means of artificial selection cannot continue indefinitely. A population may respond to selection until its mean is many standard deviations different from the mean of the original population, but eventually the population reaches a selection limit at which successive generations show no further improvement.
Although often the qualitative differences between artificial and natural selection are stressed by many evolutionary biologists to avoid the inference to selection limits for the latter, there are no scientifically valid reasons to believe that natural selection is limitless. The plasticity of the genome is not infinite, irrespective of the kind of selection pressure exercised upon a population (Lönnig, 1993).
Natural Selection and the Origin of New Genes
The observations summarized in the law of recurrent variation directly lead to the question of the origins of new genes. The probability of obtaining an entirely new functional DNA sequence (necessary, for example, for the origin of the more than five thousand extant different gene families of todays living organisms) due to gene duplications with subsequent nucleotide substitutions by point and other mutations has been calculated by several authors to be less than 1 in1050, even granting billions of years for natural selection working on random mutations (ReMine, 1993; Kunze et al., 1997). The result is, simply put, that the probability is so low that no reasonable person would expect to obtain a target or goal in any other area of life by such small chances. Due to the factual absence of completely new functional DNA sequences in mutagenesis experiments, as well as the low likelihood referenced above, the origin of new genes and gene families cannot be explained by natural selection. Additionally, the necessity of genetic engineering for organism transformation simultaneously exemplifies the fact that induced mutations in the host organism cannot substitute for the task. This is not only true for slow breeding organisms, but also for the fastest; for instance, bacteria like Escherichia coli, where thousands of generations with trillions of individuals per generation can be cultivated in the relatively short time of a few years (3,500 generations in 1 year; 1 gram of E. coli cells contains about 1013 individuals).
Natural Selection and the Origin of "Irreducibly Complex Structures"
Behe defines irreducible complexity (1998, p. 178) as follows: "An irreducible complex system is one that requires several closely matched parts in order to function and where removal of one of the components effectively causes the system to cease functioning." His mousetrap example illustrates the point: "The function of the mouse trap requires all the pieces: you cannot catch a few mice with just a platform, add a spring and catch a few more mice, add a holding bar and catch a few more. All the components have to be in place before any mice are caught." Concerning the significance of the principle of irreducible complexity for natural selection, Behe explains (p. 179):
Closely matched, irreducible complex systems are huge stumbling blocks for Darwinian evolution because they cannot be put together directly by improving a given function over many steps, as Darwinian gradualism would have it. The only possible recourse of a gradualist is to speculate that an irreducibly complex system might have come together through an indirect route - perhaps the mousetrap started out as a washing board, was changed into an orange crate, and somehow ended up as a mousetrap. One can never completely rule out such an indirect scenario, which is tantamount to trying to prove the negative. However, the more complex the system, the more difficult it becomes to envision such scenarios, and the more examples of irreducible complexity we meet, the less and less persuasive such indirect scenarios become.
In his 1996 book, Darwins Black Box, Behe discusses several examples of biological irreducible complexity, among them the cilium, and the bacterial flagellum with filament, hook, and motor embedded in the membranes and cell wall, and the biochemistry of blood clotting in man. The open questions of the different positions of Dawkins and Hitching on the famous example of the origin of the eye are discussed at some length, especially the problems of natural selection for the biochemistry of vision in the introductory chapter. He sums up his analysis as follows (1996, pp. 38-39):
Hitchings argument is vulnerable because he mistakes an integrated system of systems for a single system, and Dawkins rightly points out the separability of the components. Dawkins, however, merely adds complex systems to complex systems and calls that an explanation. This can be compared to answering the question "How is a stereo system made?" with the words "By plugging a set of speakers into an amplifier, and adding a CD player, radio receiver, and tape deck." Either Darwinian theory can account for the assembly of the speakers and amplifier, or it cant.
For a detailed anatomical and developmental study of the genesis of the eye, specifying Darwins and Dawkins fallacies of natural selection and gradualistic evolution under full quotation of the relevant passages, see Lönnig, 1989. Also, several important points (as the improbability to derive a reflecting eye from a refracting one) have been discussed by Denton (1998).
Since the origin of irreducibly complex systems or subsystems necessitates the concerted origin of many new gene-functions, the odds against natural selection of undirected mutations as the final source of these genes and structures are rising correspondingly.
NATURAL SELECTION AS METAPHYSICS AND AS SCIENCE
Poppers Critique and Recantation
Another kind of objection that was launched on the concept of natural selection originated with scholars interested in the logical structure of scientific explanations. There is a long tradition among these scholars to view the concept of natural selection to be a tautology (MacBride, 1929; Waddington, 1960; Mahner and Bunge, 1997 - excellent reviews on the debate between some 50 scientists and philosophers have been given by Bird, 1989; ReMine, 1993; and Chauvin, 1997). Waddington commented that natural selection "states that the fittest individuals in a population (defined as those which leave the most offspring) will leave the most offspring" (Waddington, 1960, p. 385), and
Natural selection is survival of the fittest, and the tautology hinges on the word fittest. When the fittest are identified by their survival then there is a tautology. We ask, who are the fittest? We are told, the survivors. We ask, who will survive? We are told, the fittest. Natural selection is then "the survival of the survivors." It is a tautology" (ReMine, 1993, p. 98).
This objection has been strongly attacked by neo-Darwinians and punctuationists alike, arguing that fitness can scientifically be defined and tested, and that the tautology argument has conclusively been disproved by many biologists and philosophers (Mayr 1991, 1997).
Perhaps the most renowned case of a criticism and later recantation concerning the metaphysics/tautology-problem of natural selection by a philosopher was Sir Karl Poppers comment that "Darwinism is not a testable scientific theory but a metaphysical research program", that is, natural selection was seen to be "almost tautologous" and at best only "a possible framework for testable scientific theories" (1974, p. 134; italics in original). In a time of rising creationism, these often quoted statements lead to an unusual amount of criticism and pressure of the evolutionary community for Popper to check, extend and reformulate his views on natural selection.
To back up his recantation four years later that "the theory of natural selection may be so formulated that it is far from tautological" (1978, p. 339), he mentioned as evidence the famous textbook example of industrial melanism of the peppered moth (Biston betularia) asserting that here "we can observe natural selection happening under our very eyes, as it were". In this case the majority of the light colored form was believed to have been replaced by a dark type better adapted to sooty trees in the wake of the industrial revolution - an example of natural selection probably well-known to every student who ever attended a course on evolutionary biology at school or university all over the world.
Poppers Case of the Peppered Moth: Still more Metaphysics than Science
Looking at the famous case of industrial melanism more than 20 years later, we have to point to the most surprising fact that the case has recently been found wanting (Sargent et al., 1998; Majerus, 1998; Coyne, 1998). Hence, we may conclude that Poppers partial retraction of his views was not necessary, at least not because of the example of the peppered moth.
After summarizing Kettlewells presentation of the Biston betularia instance, Coyne (1998) states the main points of the critical recent observations as follows: (a) The peppered moth normally doesnt rest on tree trunks (where Kettlewell had directly placed them for documentation); (b) The moth usually choose their resting places during the night, not during the day (the latter being implied in the usual evolutionary textbook illustrations); (c) The return of the variegated form of the peppered moth occurred independently of the lichens "that supposedly played such an important role" (Coyne); and (d) Kettlewells behavioral experiments have not been replicated in later investigations. Additionally, there are important points to be added from the original papers, as (e) differences of vision between man and birds and (f) the pollution-independent decrease of melanic morphs.
So Poppers case of the peppered moth as an observation against his own criticism of natural selection as a metaphysical research program consists, nonetheless, mostly of metaphysics. It may be asked: How is it possible that cases of insufficient or even false evidence for natural selection can be bolstered and presented in such a way that it appears to be so convincing and entirely compelling that even the best minds of the world can be grossly misled - even to the point of modifying a published evaluation on this topic?
For another renowned textbook-example of natural selection, which was pointed out recently to consist more of a metaphysical explanation than a scientifically valid case, see Gould for the origin of the neck of the giraffe (Gould, 1996). Moreover, as for the inherent limitations of one of the prime examples for natural selection, to wit the sickle cell allele and malaria resistance, see ReMine (1993). Moreover, one may ask whether Mayrs first four instances for natural selection mentioned above ("insecticide resistance of agricultural pests, antibiotic resistance of bacteria, industrial melanism, the attenuation of the myxomatosis virus in Australia") are really cases of natural selection or more "man-made" or "man-caused" selection.
NATURAL SELECTION AND THE LIMITED GEOGRAPHICAL DISTRIBUTION OF SPECIES
The main problem regarding natural selection and limited geographical distribution of species has aptly been summarized by the evolutionary biologist Futuyma (1998, p. 535):
[R]ange limits pose an evolutionary problem that has not been solved. A species has adapted to the temperature, salt levels, or other conditions that prevail just short of the edge of its range. Why, then, can it not become adapted to the slightly more stressful conditions that prevail just beyond its present border, and extend its range slightly? And if it did so, why could it not then become adapted to still more demanding conditions, and so expand its geographic range (or its altitudinal or habit distribution) indefinitely over the course of time? These questions pose starkly the problem of what limits the extent of adaptive evolution, and we do not know the answers. We will discuss several hypotheses, citing little evidence because little exists (Hoffmann and Blows, 1994; Bradshaw, 1991).
Part of the answer is the inherent limit of variation specified by the law of recurrent variation, i.e. the intrinsic restriction of the action of chance mutations to generate functionally new genetic material, either for one new gene or many of them indispensable for the origin of irreducibly complex structures. The absence of such "positive mutations" results in limits for natural selection.
NATURAL SELECTION AND LIVING FOSSILS
Living fossils have been totally unexpected for a theory according to which everything is in a state of permanent flux and evolution (Lönnig, 1999b). In the wording of Eldredge (1989, p. 108), "Living fossils are something of an embarrassment to the expectation that evolutionary change is inevitable as time goes by." Darwin admitted, "When I see that species even in a state of nature do vary little and seeing how much they vary when domesticated, I look with astonishment at a species which has existed since one of the earlier Tertiary periods. ...This fixity of character is marvellous" (Darwin, 1852, quoted in Ospovat, 1995, p. 201). The general explanation by neo-Darwinians is that certain species are fixed because they are adapted to non-changing environments. This explanation is doubtful for the following reasons: (a) There are hardly any constant environments over longer geologic time periods; (b) Most living fossils are found in permanently changing environments with high competition factors (Storch & Welsch, 1989); and (c) According to the modern synthesis, even in constant environments the endless generation of new advantageous mutations plus selection pressures within the species should lead to the permanent substitution of primitive structures and species by more advanced ones. So, in spite of billions of mutations in the long history of living fossils and in defiance of natural selection during millions of years, species did not diverge (see definition of natural selection at the beginning of the article). Therefore, the rich array of living fossils constitutes another serious problem for the neo-Darwinian school.
NATURAL SELECTION AND EARTH HISTORY
One of the major setbacks for the idea of a pervasive and the history-of-life-dominating process of natural selection has been the rise of what neo-Darwinians derogatorily call "neocatastrophism" (Hsü, 1986; Alvarez, 1998; Prothero, 1998). Darwin "postulated a single process, the biotic struggle of natural selection, that was uniform over all the time on the earth, proceeded always at the same rate, on a planet that ceaselessly changed in detail but never abruptly changed state" (Hsü, p. 47). Today, Darwins view is generally rejected by all informed scientists. The current question is not whether catastrophes have repeatedly interrupted natural selection worldwide, but which kinds of catastrophes are the most important ones in earth history.
THE QUEST FOR AN ALTERNATIVE
Although in this article alternatives for the origin of species cannot be discussed at length, a few points should be mentioned. As a first step into the direction of a realistic alternative to the doubtful hypothesis of the nearly omnipotent natural selection, let us shortly turn our attention to Behes arguments again. He writes, "Closely matched, irreducibly complex systems not only are tall problems for Darwinism but also are the hallmarks of intelligent design. What is design? In my definition, design is simply the purposeful arrangement of parts" (1998, p. 179). However, does this inference to intelligent design not lead us directly back into the realm of metaphysics in Poppers sense? Not necessarily. A thoroughly epistemological study to clearly distinguish between the three basic parameters for any explanation in science and other areas of life in terms of either law, chance, or design (and in special cases to discover the proportions in a combination of two or even all three of them), has recently been performed and published by Dembski (1998a, 1998b). In his "explanatory filter" the object of explanation is an event called E. The first question is whether E is a highly probable event. If it is certain that E occurs under a set of standard conditions, E is probably due to deterministic or nondeterministic natural laws. If this first prerequisite is denied, it must be determined whether E is an event of intermediate probability, that is, an event, which one can commonly anticipate to happen by chance in normal situations of life. If an event has the probability of 1 in 10 million, it will happen a 100 times in 1 billion corresponding situations. Concerning intelligent design, Dembski further explains (1998b, pp. 101-102):
But suppose that E is neither a high probability (HP) nor an intermediate (IP) event. By a process of elimination E will therefore make it all the way to the third and final decision node. In this case E is an event of small probability, or what I am calling an SP event. Our naive intuition is that SP events are so unlikely as not to occur by chance. To take an example, consider the possibility of a thermodynamic accident whereby a loaded gun (say a perfect replica of a .357 Magnum, complete with bullets) materializes in your hand, gets aimed at your favorite enemy, fires and kills him. Strictly speaking the laws of physics do not preclude such an event from happening by chance. Nevertheless, a court will surely convict you of willful homicide. Why does a court refuse to exonerate you by attributing such an event to chance? How would a jury respond to a defense that argues the gun simply materialized?
...Yet we cannot deny that exceedingly improbable events (i.e., SP events) happen by chance all the time. To resolve the paradox we need to introduce an extraprobabilistic notion, a notion I referred to as specification. If a probabilistic set-up, like tossing a coin 1,000 times, entails that an SP event will occur, then necessarily some extremely improbable event will occur. If, however, independently of the event we are able to specify it, then we are justified in eliminating chance as the proper mode of explanation. It is the specified SP events (abbreviated sp/SP) that cannot properly be attributed to chance.
For the details and a mathematical treatment of these insights see Dembski, 1998a, 1998b; for further information on a testable (that is, non-metaphysical) theory of intelligent design, see also ReMine, 1993 and Lönnig, 1998. In contrast, the modern synthesis with its main pillars of natural selection and random mutations has scientifically failed to explain the origin and history of the living world.
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