Evolutionary mechanisms

Summary of problems:

Explore Evolution describes only two evolutionary mechanisms, yet standard biology texts describe many more. The discussion of evolutionary mechanisms completely omits any reference to genetic drift, endosymbiosis, gene flow, genetic recombination. This despite the fact that prominent biologists have argued that genetic drift and symbiosis may actually be more important to the history of life than natural selection or mutation, the only mechanisms mentioned anywhere in Explore Evolution.

Full discussion:

Biologists recognize many evolutionary mechanisms, including not only natural selection and mutation, but the effects of chance fluctuations in gene frequency (genetic drift), the effects of genetic rearrangements on a chromosome (recombination), the effects of migration of genetic variants into and out of a population (gene flow) and the effects of wholesale incorporation of genetic material by one species from another species (endosymbiosis). There is an ongoing debate within evolutionary biology over whether genetic drift is more influential than natural selection on the course of evolution. Other biologists have suggested that endosymbiosis may be even more important, and continue to test that hypothesis. If Explore Evolution really intended to present ongoing scientific controversies regarding evolution, those debates over evolutionary mechanisms would have a prominent place. And yet, in discussing "the creative power of natural selection," EE states:

Some people use the term evolution to refer to a cause or mechanism of change. When evolution is used in this way, it usually refers to the mechanism of natural selection (acting on random variations and mutations). This third use of evolution affirms that the natural selection/mutation mechanism is capable of creating new living forms, and has thus produced the major changes we see in the history of life (as represented by Darwin's Tree of Life.)
EE, p. 8

It's certainly true that scientists refer to evolution in this broad mechanistic sense, but no biologist restricts that discussion to mutation and natural selection. Biologist Michael Lynch recently pointed out that the mistake Explore Evolution makes is a common one:

Evolutionary biology is treated unlike any science by both academics and the general public. For the average person, evolution is equivalent to natural selection, and because the concept of selection is easy to grasp, a reasonable understanding of comparative biology is often taken to be a license for evolutionary speculation. It has long been known that natural selection is just one of several mechanisms of evolutionary change, but the myth that all of evolution can be explained by adaptation continues to be perpetuated by our continued homage to Darwin's treatise in the popular literature. There is, of course, a substantial difference between the popular literature and the knowledge base that has grown from a century of evolutionary research, but this distinction is often missed by nonevolutionary biologists [including the authors of EE].

[E]volution is a population-genetic process governed by four fundamental forces. Darwin articulated one of those forces, the process of natural selection, for which an elaborate theory in terms of genotype frequencies now exists. The remaining three evolutionary forces are nonadaptive in the sense that they are not a function of the fitness properties of individuals: mutation is the ultimate source of variation on which natural selection acts, recombination assorts variation within and among chromosomes, and genetic drift ensures that gene frequencies will deviate a bit from generation to generation independent of other forces.

[A]ll four major forces play a substantial role in genomic evolution. It is impossible to understand evolution purely in terms of natural selection, and many aspects of genomic, cellular, and developmental evolution can only be understood by invoking a negligible level of adaptive involvement.
Michael Lynch (2007) "The frailty of adaptive hypotheses for the origins of organismal complexity," Proceedings of the National Academy of Sciences 104(S1):8597-8604

Explore Evolution provides a perfect example of the errors Lynch describes. Genetic drift and recombination do not occur in the index to the book, nor the glossary, nor does the EE passage quoted above even acknowledge the existence of evolutionary processes other than natural selection acting on mutations. Evolutionary biology textbooks typically devote at least a full chapter to discussing the role of genetic drift (e.g., chapter 7 in Ridley's Evolution, chapter 11 in Futuyma's Evolutionary Biology), and introductory textbooks address the topic as well (e.g., p. 400 in Miller and Levine's Biology, pp. 450-451 in Campbell and Reece's Biology, 6th ed., and pp. 393-399 in Raven and Johnson's Biology, 5th ed.). There is no way to "explore evolution" accurately without including a discussion of all the major evolutionary processes. The inaccurate and biased presentation of even such basic knowledge demonstrates how EE would misinform and miseducate students.

It should not come as a surprise to learn that the caricature of evolution as "natural selection (acting on random variations and mutations)" is a common creationist trope, and the discussion of the definitions of evolution in EE is basically identical to that in a seminal work of ID creationism, Phillip Johnson's Darwin on Trial (with one interesting omission):

"Evolution" in the Darwinist usage implies a completely naturalistic metaphysical system, in which matter evolved to its present state of organized complexity without any participation by a Creator. But "evolution" also refers to much more modest concepts, such as microevolution and biological relationship.
Phillip E. Johnson (1991) Darwin on Trial, Regnery Gateway, Washington, DC, p. 151

Explore Evolution employs the same argument, but lets innuendo replace Johnson's forthright advocacy of "a Creator." This is in keeping with EE's habit of parroting creationist criticisms of evolution and attempting to cloak the religious nature of those objections through omission and obfuscation.

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