Excerpts from Ernst Mayr’s “What Evolution Is”

(Basic Books, 2002)

Ó 2005, Casey Luskin www.ideacenter.org

The late Ernst Mayr was one of the most influential evolutionary biologists in America during the 20th century. Those interested in evolutionary theory would do well to understand the words penned by Mayr in his final book, “What Evolution Is,” published after over 60 years as a leading evolutionist. What follows are some highlights of the thoughts shared by Dr. Mayr in “What Evolution Is:”

It should be stated at the outset that Mayr is an evolutionist who believes the evidence for evolution is very great. Thus, to whatever extent I argue for weaknesses in evolutionary theory, I want to acknowledge that Mayr himself believed that evolution could overcome these alleged obstacles. As far as I can tell, Mayr remained a committed evolutionist to the end.

Mayr begins by revealing that part of his motivations for writing the book was an intent to challenge to believers in Genesis with the evidence for evolution:

“[M]y account is directed to those creationists who want to know more about the current paradigm of evolutionary science, if for no other reason than to be able to better argue against it. I do not expect to convert this kind of reader, but I want to show him or her how powerful the evidence is that induces the evolutionary biologist to disagree with the account presented in Genesis.” (p. xiii-xiv)

For those who accept Mayr’s views, it is apparent that the implications of evolution are very far reaching. Mayr believes the evidence shows that our behavior and thoughts are essentially completely determined by evolutionary processes:

“But the importance of this concept [evolution] goes far beyond biology. The thinking of modern humans, whether we realize it or not, is profoundly effected—one is almost tempted to say determined—by evolutionary thinking.” (p. Xiii)

If all human thinking and behavior has been “determined” by evolution, then Mayr is indeed correct that evolutionary theory has implications which go far beyond the science of biology. Yet Mayr concedes that his bold conclusions about evolution are not necessarily based upon strong empirical proof, because evolution is a mere historical inference:

“Evolution is a historical process that cannot be proven by the same arguments and methods by which purely physical or functional phenomena can be documented. Evolution as a whole, and the explanation of particular evolutionary events, must be inferred from observations.” (p. 13)

A committed evolutionist, Mayr believes that evolutionary inferences “have by now been tested successfully so often that they are accepted as certainties.” (p. 13) However close scrutiny of the evidence may reveal that evolution does not sit on as firm a foundation as Mayr would like to think.

Difficulties finding evidence for evolution are well illustrated in the case of the fossil record. Mayr explains that the fossil record is full of “gaps” where taxa “often appear quite suddenly:”

“Given the fact of evolution, one would expect the fossils to document steady change from ancestral forms to the descendants. But this is not what the paleontologist finds. Instead her or she finds gaps in just about every phyletic series. New types often appear quite suddenly, and their immediate ancestors are absent in the earlier geological strata. The discovery of unbroken series of species changing gradually into descending species is very rare. Indeed the fossil record is one of discontinuities, seemingly documenting jumps (saltations) from one type of organisms to a different type.” (p. 14)

Of course inferring descent from the fossil record might be easier if we had some independent basis to know that various extinct species were related. The concept of “homology” thus comes into play, where evolutionists argue that certain body structures in different organisms are historically related, as there was “partial inheritance of the same genotype from the common ancestor.” (p. 27) However, even homology itself is merely an inference:

“The claim that certain characteristics in rather distantly related taxa are homologous is at first merely a conjecture. The validity of such an inference must be tested by a series of criteria (Mayr and Ashlock 1991), such as position in relation to neighboring organs, the presence of intermediate stages in related taxa, similarity of ontogeny, existence of intermediate conditions in fossil ancestors, and agreements with evidence provided by other homologies. Homology cannot be proven; it is always inferred.” (p. 27)

Homology can receive evidentiary support when evolutionists compare characteristics of organisms and find that they line up in a consistent way which indicates a particular pattern of ancestry. These hypotheses about ancestry were typically called “phylogenetic trees.” Before the biotechnology revolution, evolutionists typically compared macro-morphological characteristics when constructing such “trees.” With our current ability to determine the precise molecular sequence of DNA and proteins, many evolutionists hoped that phylogenetic trees based upon DNA would match those created by skeletal structure and other “macro-features.” Mayr recounts the molecular revolution below:

“When it was discovered that the molecules that make up genes undergo evolution and have a phylogeny just like morphological characters, it was hoped that a definite phylogeny of organisms could soon be constructed; molecular evidence would enable a decision whenever the morphological data were ambiguous. Alas, things did not turn out to be quite so simple, for this reasoning ignored the phenomenon of mosaic evolution. Each component of the genotype can evolve somewhat independently of the rest of the genotype. Endeavors to construct phylogenetic tress on the basis of evolution of one particular molecule frequently produced results that were clearly in conflict with a massive amount of morphological and other evidence. For technical reasons the molecules that were first used for such analyses were ribosomal RNA and mitochondrial DNA. Unfortunately these molecules often went their own evolutionary way.” (p. 51)

What does it mean to go their “own evolutionary way?” I can only take it to mean that they evolved in a pattern which we wouldn’t expect if common ancestry were the case. Mayr is confident that eventually a firm consensus will arrive among those creating molecular phylogenies. But the finding that molecules go their “own evolutionary way” indicates that the molecular (i.e. DNA / proteins sequence) data was not giving a consistent picture of evolutionary history and ancestry. In other words, the data did not support a clear and simple picture about common descent. Constructing phylogenetic trees based upon “homology” runs into trouble when one encounters “convergent evolution:”

“The validity of a classification largely depends on the proper evaluation of the characters on which it is based. Owing to their radial symmetry, Cuvier combined the coelenterates and the echinoderms in the higher taxon Radiata. However, it was soon shown how different the two radial taxa are in just about all their characters, and it was realized that radial symmetry of the echinoderms was due to convergent evolution of a basically bilateral body plan. Metamerism is characteristic for several phyla of animals, particularly the annelids, arthropods, and vertebrates. However, much evidence suggests that this character originated independently in the three mentioned groups. One must always make a careful test of homology when on encounters such similarities in otherwise rather different groups to determine whether or not their similarity is due to convergence. But convergent similarity may also develop when two unrelated taxa independently lose the same characteristic.” (p. 61-62)

Mayr suggests careful analysis can solve these problems, but the data make it difficult for evolution to make consistent predictions: sometimes similarity is homologous and implies ancestry, but sometimes it is just “convergent similarity,” the result of historically independent, but similar evolutionary paths. In other words, similarity implies ancestry, except for when it doesn’t. The inferences supporting common descent can have a very weak basis.

Sometimes common descent is strongly challenged by the data. Mayr recounts that “Photosensitive, eyelike organs have developed in the animal series independently at least 40 times…” (p. 205) It is incredible that such complexity would evolve “independently”—again, similarity implies ancestry, except for when it doesn’t. Even more significantly, Mayr finds that some of the same genes are used in eye construction despite the fact that these eyes supposedly evolved in completely separate lineages:

“It had been shown that by morphological-phylogenetic research that photoreceptor organs (eyes) had developed at least 40 times independently during the evolution of animal diversity. A developmental geneticist, however, showed that all animals with eyes have the same regulator gene, Pax 6, which organizes the construction of the eye. It was therefore concluded at first concluded that all eyes were derived from a single ancestral eye with the Pax 6 gene. But then the geneticist also found Pax 6 in species without eyes, and proposed that they must have descended from ancestors with eyes. However, this scenario turned out to be quite improbable and the wide distribution of Pax 6 required a different explanation. It is now believed that Pax 6, even before the origin of eyes, had an unknown function in eyeless organisms, and was subsequently recruited for its role as an eye organizer.” (p. 113)

Mayr attempts to give a plausible evolutionary explanation for why so many types of organisms use the same genes – through completely independent evolution – to construct eyes. However, given that this identical usage of the Pax 6 gene supposedly evolved so many (40+) times in evolutionary history, it almost appears that life was “pre-destined” to evolve eyes in this manner. Mayr recounts that this independent evolution is not uncommon:

“That a structure like the eye could originate numerous times independently in very different kinds of organisms is not unique in the living world. After photoreceptors had evolved in animals, bioluminescence originated at least 30 times independently among various kinds of organisms. In most cases, essentially similar biochemical mechanisms were used. Virtually scores of similar cases have been discovered in recent years, and they often make use of hidden potentials of the genotype inherited from early ancestors.” (p. 206-207)

Mayr attributes the re-usage of the same parts in distantly related organisms to “hidden potentials of the genotype” but one must ask if this is consistent with common descent? Again, similarities indicate homology, and thus common descent, except for when they don’t. The logic behind inferring homology and common descent is very weak. Furthermore, the re-usage of similar parts in distantly related organisms might best be explained by common design, not common descent.

Turning away from taxonomy, Mayr’s book reveals a very interesting fact about his views Mayr is a skeptic that birds evolved from dinosaurs. While many evolutionists do adhere to the view that birds are descendants of dinosaurs, Mayr provides a list of reasons why he believes this is not the case:

“Refutation of the Dinosaurian Origin of Birds

1. Age—The dinosaurs structurally most similar to birds are very recent (80-110 million years ago), whereas Archaeopteryxis a great deal older (145 million years ago) and no birdlike dinosaurs are known from the lower Jurassic or Triassic that could qualify as ancestors of birds.

2. The three digits of the hand of dinosaurs are 1,2,3, those of a bird are 2,3,4. It is quite impossible to derive the avian digis from those of dinosaurs.

3. Teeth—Theropods have recurved, flattened, serrated teeth, quite different from the simple peglike, waisted, nonserrated teeth of Archaeopteryx and other early birds.

4. The pectoral girdle and anterior extremities of the late theropod dinosaurs are much too small and weak to have served as the foundation of a powerful wing to lift an incipient bird from the ground. No factors are known that could have caused a sudden drastic growth of the anterior extremities.

5. The leading aerodynamic experts of bird flight claim that an origin of flight from the ground up is a near impossibility.” (p. 68)

Near the end of his book, Mayr turns to the origin of humans, where he makes some startling claims. Mayr acknowledges that much of the evidence for the evolution of humans is nonexistent in the fossil record, as “we have no fossil documentation of the human ancestry between 14 and 4.5 million year ago” (p. 69) and also, “there is no documentation of the branching event between the hominid and the chimpanzee lineages.” (p. 239) Furthermore, “most hominid fossils are extremely incomplete” causing the problem that “[s]ubjectivity is inevitable in the reconstruction of the missing parts.” (p. 239) But what about the fossils that we do have—do they indicate a fossil transition from ape-like species to human-like species? Mayr recounts:

“[T]he reconstruction of the steps of hominization proved to be very difficult. … More disturbingly, it turned out to be quite impossible to establish the hoped for smooth continuity. This, of course, was largely due to the incompleteness of the fossil record, but not entirely so, and this is what was so disturbing. As we shall see (see below for details), some fossil types were relatively common and widespread, such as Australopithecus africanus, A. afarensis, and Homo erectus, but they were seemingly separated by discontinuities from their nearest ancestors and descendants. This is particularly true for the break between Australopithecus and Homo.” (p. 238)

According to Mayr, the record is not entirely incomplete, and it really shows a distinct “break” between the australopithecine apes and the first human-like members of our genus, Homo.

The australopithecines were essentially very much like modern apes which did exhibit evolution approaching the characteristics of our genus Homo:

“Although bipedal, Australopithecus apparently still lived mostly arboreally and much of its body structure, like the length of its arms, was quite different from that of modern man.” (p. 242)

“The gracile Australopithecus populations lived from 3.8 to 2.4 mya. In their body size and smallness of the brain they were apes. What is most noteworthy, however, is that they did not change very much in the whole 1.5-million-year-long period; it was a period of stasis. … There was no approach toward the characters of Homo over this long period.” (p. 243)

“[E]xcept for bipedalism and some tooth characters, the australopithecines shared almost all other characters with the chimpanzees. And, what is surely more important they had none of the most typical Homo characters. They lacked a large brain, they did not produce flaked stone tools, they still had strong sexual dimorphism of apes, they had long arms and short legs, and their body size was small. Also we must distinguish between two forms of bipedalism, that of the arboricolous australopithecines and that of the exclusively terrestrial humans. It is probably correct to claim that in the aggregate of their characteristics, the australopithecines were closer to chimpanzees than to Homo.” (p. 244)

Mayr believes that “the step from the Australopithecus apelike stage to the Homo stage was clearly the most important event in the history of hominization” (p. 244) but yet when we look at the fossil data, Australopithecus and Homo “were seemingly separated by discontinuities.” (p. 238) In other words, it seems that the fossil record does not document a clear transition from Australopithecus to Homo. Mayr attributes this rapid evolution to something like a punctuational account of human origins:

“As so often occurs in speciational evolution, after an enormous spurt in a short time, Homo erectus experienced a period of stasis and, aside from the increase in brain size, not much changed in the evolution from H. erectus to H. sapiens.” (p. 249)

Mayr’s account may be plausible, but it nonetheless thus so happens that the evidence for evolution seems to be missing in just the right places.

From comparisons of characteristics to create phylogenetic trees to fossil evidence of key evolutionary transitions, Mayr seems to be making a case for evolution that is often lacking in evidence. Despite Mayr’s belief that “[t]he evidence for evolution is now quite overwhelming,” perhaps it is a house of cards built upon shaky inferences unwarranted by the data.