Summary of problems:
Evolutionary theory predicts relatively smooth and incremental transitions, not the sudden emergence of new traits or species. Even so, Explore Evolution discusses "whether natural selection can produce fundamentally new forms of life, or major innovations in the anatomical structure of animals" without ever explaining how students ought to distinguish "fundamentally new forms" of life from merely "new" forms, nor how "major innovations" can be distinguished from more mundane "innovations." The assumption that any trait would spring forth, fully formed, without precedent, is not a prediction of evolution, nor are these concepts in general use by biologists.
As noted above, real textbooks about evolution distinguish several evolutionary mechanisms, including natural selection and mutation, but also genetic drift and gene flow, as mechanisms for evolutionary change. In particular, mutation is a change in the DNA of a cell in a single organism, and if it happens in a cell which goes on to produce an egg or sperm cell, it can be passed on to all the descendants of that individual. This makes mutation "the origin of genetic variation" (Futuyma, 1998, Evolutionary Biology, 3rd ed., ch. 7). When Explore Evolution speculates about "whether natural selection can produce fundamentally new forms of life, or major innovations" in anatomy (p. 9), it wrongly omits the generative power of mutation, as well as other evolutionary mechanisms, several of which may be more important to the course of evolution than natural selection.
The discussion of whether evolution is "creative or conservative" (section heading, p. 9) in Explore Evolution is profoundly confusing because it fails to distinguish between different evolutionary processes, and between the levels at which they operate. For instance, the discussion about whether natural selection itself is "creative" ignores the role of other mechanisms in generating variation, and the difference between novelty at a genetic level, at a genomic level, or at a population level. Also, EE's focus on whether natural selection can produce "fundamentally new forms of life" fails to describe over what time scale it might be operating, nor what processes scientists hypothesize in addition to (not instead of) natural selection.
More worrisome in the educational setting, the authors of Explore Evolution misrepresent several of the authors that they quote regarding the "creative" power of natural selection. They write:
Zoologist Ernst Mayr writes that natural selection is a "positive, constructive force," and adds "one can go even further and call natural selection a creative force."EE, p. 9
As the footnote points out, these two quotations come from different sources; Mayr did not "add" one phrase to the other. Neither does the first quotation refer to Mayr's own views on whether natural selection was a "creative" force, he was pointing out that Charles Darwin "considered selection not a purely negative force that eliminates the unfit, but a positive, constructive force that accumulates the beneficial" (Ernst Mayr, 1964, "Introduction" to On the Origin of Species by Charles Darwin: A Facsimile of the First Edition, Harvard University Press: Cambridge, MA. p. xvii). The latter quotation comes from a passage that addresses exactly the misconceptions EE promotes, and is worth quoting at length.
An understanding of the working of natural selection is the key to the Darwinian theory of evolution. I know of no other scientific theory that has been as misunderstood and misrepresented as greatly as the theory of natural selection. First of all, it is usually represented as strictly negative, as a force that eliminates, a force that kills and destroys. Yet Darwin, by his choice of the name "selection," clearly emphasized the positive aspects of this force. Indeed, we now know that one can go even further and call natural selection a creative force. Second, natural selection is not an all-or-none phenomenon. The typologist, the follower of Plato, seems to think that alternatives are always either good or bad, black or white, worthy of preservation or doomed to rejection. This viewpoint is represented in two statements by well-known contemporary philosophers, chosen at random from the recent literature: "Natural selection requires life and death utility before it can come into play"; and "Unsuccessful types will be weeded out by the survival of the fittest but it cannot produce successful types."
Actually, types in the sense of these statements do not exist; only variable populations exist. No one will ever understand natural selection until he realizes that it is a statistical phenomenon. In order to appreciate this fully, one must think in terms of populations rather than in terms of types [or EE's "forms" -ed.].
A further consideration will help to make the role of natural selection even clearer. Not the "naked gene" but the total phenotype is exposed to selection. A gene occurring in a population will contribute toward very many phenotypes. In some cases these phenotypes will be successful, in others they will not. The success of the phenotypes will depend on the fitness of the particular gene, within the framework of the gene pool of this population. And this again will be an essentially statistical phenomenon.
Let us also remember that recombination, not mutation as such, is the primary source of the phenotypic variation encountered by natural selection. The usual argument of the anti-Darwinian is: "How can an organism rely on the opportune occurrence of a favorable mutation whenever one is needed, considering that most mutations are deleterious? Surely all organisms would be doomed to extinction of in times of need they had to rely on such rare events?" Those who ask such questions confuse genetic variability and phenotypic variability. To be sure, mutation is ultimately the source of all genetic variation. But natural selection operates not at the level of the gene but at the level of the phenotype. Further, the main source of phenotypic variation is recombination rather than mutation, and this source of variation is ever present. With every individual differing genetically from every other one, every phenotypic character is variable, showing deviations of varying intensities and directions around the mean. Under normal conditions, selection will favor the mean (stabilizing selection), but if a deviation in any direction should be required by a newly arising selective force, the material is instantaneously available to respond to this force (directive selection).
Natural selection in this modern nontypological interpretation is an exceedingly sensitive instrument. The phenotype in nearly every case is actually a compromise between a number of conflicting selective forces.Ernst Mayr (1962) "Accident or Design: The Paradox of Evolution," in The Evolution of Living Organisms, (proceedings of the Darwin Centenary Symposium of the Royal Society of Victoria), and reprinted in Mayr (1976) Evolution and the Diversity of Life: Selected Essays, Harvard University Press:Cambridge, MA, ch. 4, pp. 36-38
Given that it is the combinations of genes which produces the final organism, recombination of genes during cell replication and sexual reproduction plays a critical role in generating variation within the population. Natural selection acts on combinations of genes as much as it operates on the individual genes themselves, and the sum total of the selection on particular genes and particular combinations of genes can and does produce biological novelties. It is fair to say that this process of selecting genes and gene combinations makes natural selection "an editor" (EE, p. 9, emphasis original). Editing can be creative work; EE would have benefited from a particularly creative editor, and good authors often regard their editors as collaborators whose creativity is necessary for the final product.
Explore Evolution hedges a bit on this point, arguing that it is not enough for something to be new, it must be "fundamentally new." By this they seem to mean a "major innovation in the anatomical structure of animals" (or plants, fungi and other living things, presumably). Unfortunately, it is not clear what makes an innovation "major," any more than it is clear when a novelty is "fundamentally new," rather than simply new. More importantly, it is not clear how quickly novelties must appear in a population in order to qualify as "major innovations" or "fundamentally new." The accumulation of small novelties over many generations is the hallmark of evolutionary change. The sudden appearance of new structures without any intermediates is not an evolutionary prediction, and no examples of such a change exist to require evolutionary explanations.
There are indeed many innovations which cannot be explained by natural selection alone. The mitochondria and chloroplasts are a perfect example, discussed in more detail in our critique of the chapter on Natural Selection. Endosymbiosis, a sort of cooption at the cellular level, is comparable to the role of recombination within the genome and gene flow in populations, and the authors of Explore Evolution would have done well to have expanded their exploration to include the full range of evolutionary processes. It would have benefited their own writing, and helped any students unfortunate enough to have this book inflicted upon them.