Ernst Mayr, Excerpts from "What Evolution Is"

Basic Books 2001.

- “The thinking of modern humans, whether we realize it or not, is profoundly effected — one is almost tempted to say determined—by evolutionary thinking.” (pg. Xiii)

- [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.” (pg. Xiii-xiv)

- “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.” (pg. 13)

- “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.” (pg. 14)

- “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.” (pg. 27)

- ‘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.” (pg. 51)

- “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. For example, it is very probable that nonsegmented groups such as the molluscs, Echiura, and Pogonophora descended from segmented ancestors.” (pg. 61-62)

- “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.” (pg. 68)
>    6.[W]e have no fossil documentation of the human ancestry between 14 and 4.5 million year ago.” (pg. 69) 7.“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.” (pg. 113) “Photosensitive, eyelike organs have developed in the animal series independently at least 40 times…” (pg. 205) “The origin of eyes in 40 branches of the evolutionary tree was always considered to be an independent convergent development. Molecular biology has now shown that this is not entirely correct. A regulatory master gene (called Pax 6) has recently been discovered that seems to control the development of eyes in the most diverse branches of the tree (see Chapter 5).
>      However, this gene occurs also in taxa whose species have no eyes.  Pax 6 is apparently a basic regulatory gene, presumably involved in some other functions in the nervous system. Molecular biology has discovered a number of other such basic regulatory genes whose existence in some cases goes back to a time before the major animal phyla had branched.  When survival is favored by the acquisition of a new structure or other attribute, selection makes use of all available molecules already present in the genotype.  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.” (Pg. 205-207) 8.“The importance of this interaction of genes was not fully realized until the discovery of the regulatory genes, like hox and pax genes. With these genes we can observe verydrastic interactions, but minor interactions among genes are very common. The question of what all these interactions add up to is controversial But there is a good deal of indirect evidence for the existence of an “internal balance” of the genotype or, as it has been called a “cohesion of the genotype.” It ha been postulated that this is a conservative element in evolution and accounts for the stasis in so many evolutionary lineages.” (pg. 127)
>    9.“According to Darwinian theory, evolution is a populational phenomenon and should therefore be gradual and continuous.  This should be true not only for microevoltuion but also for macroevolution and for the transition between the two.  Alas, this seems to be in conflict with observation.  Wherever we look at the living biota, whether at the level of the higher taxa or even at that of the species, discontinuities are overwhelmingly frequent.  Among living taxa there is no intermediacy between whales and terrestrial mammals, nor between reptiles and either birds or mammals. All 30 phyla of animals are separated from each other by a large gap. There also seems to be a large gap between the flowering plants (angiosperms) and their nearest relatives. The discontinuities are even more striking in the fossil record. New species usually appear in the fossil record suddenly, not connected with ancestors by a series of intermediates.” (pg. 189-he goes on to attempt to explain these discrepancies.) 10.“Bats originated from an insectivorelike ancestor within a few million years, but have hardly changed in the basic body plan in the ensuing 40 million years. The origin of whales happened very rapidly, in terms of geological time, compared to the subsequent essential stasis of the new structural type.” (pg. 196)
>   11."Alas, the reconstruction of the steps of hominization proved to be very difficult. First of al, the first fossils that were found were the most recent ones.  So the path of reconstruction was not from ape to human but fro man back to ape.  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.” (pg. 238) 12.“Unfortunately, no hominid fossils—nor such of a fossil chimpanzee—are as yet known for the period between 6 and 13 mya. Thus there is no documentation of the branching event between the hominid and the chimpanzee lineages. To make matters worse, most hominid fossils are extremely incomplete. They may consist of part of a mandible, or the upper part of a skull without face and teeth, or only part of the extremities. Subjectivity is inevitable in the reconstruction of the missing parts.” (pg. 239)
>   13.“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.” (pg. 242) 14.“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. To be sure there were differences between the southern African A. africanus and the eastern African A. afarensis, who lived at somewhat different times, but the differences might also be attributed to geographic variation induced by climatic and other environmental conditions. There was no approach toward the characters of Homo over this long period.” (pg. 243)
>   15.“The australopithecines were bipedal for more than 2 million years and yet over this whole period there was no significant change in the size of their brain. Tool use, likewise, has been downgraded in importance owing to the discovery of extensive tool use by chimpanzees and of rudimentary too use by corvids and other animals. Furthermore, except for bipedalism and some tooth characters, the australopithecines hared almost al 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. Indeed, the step from the Australopithecus apelike stage to the Homo stage was clearly the most important event in the history of hominization.” (pg. 244) 16.“This shift [to Homo] was the most fundamental one in all of hominid history. It was a far greater change than the habitat shift from rain forces to tree savanna and resulted in the evolution of a series of important diagnostic characters of the new genus Homo. Brain size rose quickly and more than doubled in H. erectus. Sexual dimorphism declined from a 50 percent to a 15 percent higher weight of the males. The teeth, particularly the molars, became much smaller. The arms shortened and the legs lengthened. Early Homo seems to have relied on fire not only for protection but apparently also for cooking.” (pg. 245)
>   17.““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.” (pg. 249)

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Ernst Mayr, Excerpts from "What Evolution Is"

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