APPENDIX A

WHAT CRITICISMS HAVE BEEN MADE OF EVOLUTIONARY THEORY?

The story of evolution as it was worked out during the past fifty years continues to be attacked and criticized. The critics either hold an entirely different ideology, as do the creationists, or they simply misunderstand the Darwinian paradigm. An author who says, “I cannot believe that the eye evolved through a series of accidents,” documents that he or she simply does not understand the two-step nature of natural selection. A typologist, not used to population thinking, will indeed have major difficulties appreciating the amount of genetic variability available to selection in natural populations.

All theories of Darwinism are subject to rejection if they are falsified. They are not unalterable like the revealed dogmas of religions. The history of evolutionary biology reports numerous cases of evolutionary theories that were eventually rejected. The belief that a gene can be the direct object of selection is one such refuted theory. An inheritance of acquired characters is another one.

In the preceding chapters I endeavored to present the story of the phenomena and processes of evolution as seen by contemporary evolutionists. These conclusions are not accepted by everybody, and it might be worthwhile to give a short summary of some of the criticisms and the responses to them by the evolutionists. I also discuss some biological phenomena considered by some authors to be in conflict with Darwinism.

Creationists

The claims of the creationists have been refuted so frequently and so thoroughly that there is no need to cover this subject once more. I refer to the publications by Alters, Eldredge, Futuyma, Kitcher, Montagu, Newell, Peacocke, Ruse, and Young listed in the bibliography (see Box 1).

Punctuated Equilibria

The claim has been made by some authors (Gould 1977) that the occurrence of punctuated equilibria is in conflict with gradual Darwinian evolution. This is not correct. Even punctuated equilibria, which, at first sight, seem to support saltationism and discontinuity, are in fact strictly populational phenomena, and therefore gradual (Mayr 1963). They are in no respect whatsoever in conflict with the conclusions of the evolutionary synthesis (see Chapter 10).

Neutral Evolution

It was claimed by Kimura (1983) and others that neutral evolution is in conflict with Darwinism. This is not correct, since the assumption in the theory of neutral evolution is that the gene is the object of selection, rather than the individual. However, in reality, it is the individual as a whole that is the target. Under these circumstances, there is no conflict with Darwinism when in the selection of certain favorite individuals some neutral gene replacements may be transmitted to the next generation as incidental components of the favored genotype (see Chapter 10).

Morphogenesis

It is claimed by some authors that the phenomena of morphogenesis, and in particular the processes of development, are in conflict with Darwinism. Even though many of the causal phenomena of development are still insufficiently understood, what is understood is entirely compatible with a Darwinian explanation. It seems that some of those who raise these criticisms assume that only the adult phenotype, the last stage of development, is exposed to selection. In reality, every stage of a developing organism, from the fertilized egg (zygote) on to old age, is constantly subjected to selection. However, the fate of postreproductive individuals is of no relevance to evolution (see Chapter 6).

Causes for Misunderstandings

There are a number of reasons why the evolutionary process is so often misunderstood. Let us look at some of these reasons.

Multiple simultaneous causations. Authors frequently look at only one of the causations of a particular evolutionary phenomenon: either the proximate or the evolutionary causation. This may lead to wrong conclusions because any evolutionary phenomenon is the result of the simultaneous occurrence of both proximate and ultimate causations. Multiple causations are involved in all selection processes because chance phenomena occur simultaneously with selection. To give an example, speciation is never merely a matter of genes or chromosomes, but also of the nature and geography of the populations in which the genetic changes occur. Geography and the genetic changes in populations affect the speciation process simultaneously.

Pluralistic solutions. Almost all evolutionary challenges have multiple solutions. During speciation, for instance, premating isolating mechanisms originate first in some groups of organisms, and in others postmating mechanisms originate first. Geographic races are sometimes phenotypically as distinct as true species without being reproductively isolated; on the other hand, phenotypically indistinguishable species (sibling species) may be fully isolated genetically. Polyploidy and asexual reproduction are important in some groups of organisms, but totally absent in others. Chromosomal reconstruction seems to be an important component of speciation in some groups of organisms, but does not occur in others. Some groups speciate profusely, whereas in others speciation seems to be a rare event. Gene flow is rampant is some species, but drastically reduced in others. One phyletic lineage may evolve very rapidly, while geographically isolated species may remain in complete stasis for many millions of years. In short, there are multiple possible solutions to most evolutionary challenges, even though all of them are compatible with the Darwinian paradigm. The lesson one must learn from this pluralism is that sweeping generalizations are rarely correct in evolutionary biology. Even when something occurs “usually,” this does not mean that it must always occur (see Chapter 10).

Mosaic evolution. I have repeatedly called attention to the highly variable rates of evolution. This is true not only for sister lineages, but also for components of a single genotype. As an example, I discussed the divergence between chimpanzee and man since their descent from a common ancestor. In this case some of the protein genes have not changed at all, while those that contribute in the human lineage to the development of the central nervous system have undergone extremely rapid evolution. Why some lineages seem to be able to enter a stage of complete stasis (“living fossils”), lasting for many millions of years, is still not understood (see Chapter 10).

The Findings of Molecular Biology

It is sometimes claimed that the findings of molecular biology necessitate a complete revision of the Darwinian theory. This is not the case. All the findings of molecular biology relevant to evolution deal with the nature and the origin of genetic variation. Even though this includes some unexpected phenomena, such as transposons (genes that can “jump” from one chromosome or position to another), they merely affect the nature and the amount of the available variation, and all of this variation is ultimately exposed to natural selection, and thus is part of the Darwinian process. The molecular discoveries of the greatest evolutionary importance are the following:

1. The genetic program (DNA) does not by itself provide the building material of a new organism, but is only a blueprint (information) for making the proteins of the phenotype.

2. The pathway from nucleic acids to proteins is a one-way street. Proteins and information contained in them cannot be translated back into nucleic acids.

3. Not only the genetic code, but in fact most of the basic molecular cellular mechanisms are the same in all organisms from the most primitive prokaryotes to humans (see Chapter 5).

Unanswered Questions

Darwinian evolutionists have every reason to be proud of the paradigm of evolutionary biology that they have constructed. Every attempt in the last 50 years to refute one or the other assumption of Darwinism has been invalidated. Furthermore, no competing evolutionary theory has been proposed, certainly none that was in any way successful. Does this mean that we now fully understand the evolutionary process in all of its details? The answer to this question is a qualified “No.”

In particular, there is one problem that is not yet entirely solved. When we look at what happens to the genotype during evolutionary change, particularly relating to such extreme phenomena as highly rapid evolution and complete stasis, we must admit that we do not fully understand them. The reason for this is that evolution is not a matter of changes in single genes; evolution consists of the change of entire genotypes. It was realized rather early in the history of genetics that most genes are pleiotropic, that is, a single gene may have simultaneous effects on several aspects of the phenotype. Likewise, it was found that most components of the phenotype are polygenically determined, that is, are affected by multiple genes. Such frequent, in fact universal, interactions among genes are of decisive importance for the fitness of individuals and for the effects of selection. Yet, they are singularly difficult to analyze. Most population genetics still focuses on additive gene effects and on the analysis of single gene loci. This is why the study of phenomena such as evolutionary stasis and the constancy of body plans is so refractory to analysis. There are many indications that separate domains exist within a genotype and that certain gene complexes have an internal cohesion that resists breakage by recombination. Up to now, however, these are only ideas; their genetic analysis still lies in the future. The structure of the genotype is perhaps the most challenging remaining problem of evolutionary biology.