"Speciation"? It's All in the Definition - Evolution News & Views

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"Speciation"? It's All in the Definition


Specious Speciation:
Response to the TalkOrigins "Speciation FAQ"


FULL RESPONSE (PDF)

Other Installments:
Post 1: Specious Speciation: The Myth of Observed Large-Scale Evolutionary Change
This Post (Part 2): "Speciation"? It's All in the Definition
Post 3: Plants, Polyploidy, and Evolutionary Dead Ends
Post 4: Uncooperative Fruit Flies Refuse to Speciate in Laboratory Experiments
• Post 5: Speciation Fail: Single Bona Fide Example of Animal Speciation is Later Retracted
Post 6: Does the Evidence for Speciation Come from Nature or Groupthink?
The TalkOrigins "Observed Instances of Speciation" FAQ claims it "discusses several instances where speciation has been observed." The most important question is whether these examples show significant biological change has occurred. But my full response to the "Speciation FAQ" shows:

  • As a primary finding, none of the examples demonstrate that Darwinian evolution is capable of causing large-scale evolutionary change.
  • As a secondary finding, the vast majority of the examples do not even meet the standard definition of "speciation."

To understand why both (1) and (2) are the case, we first need to understand the implications of how evolutionary biologists typically define "species."

Evolutionary biologists typically define "species" as a reproductively isolated population of individuals. For example, the FAQ quotes the great neo-Darwinian evolutionary biologist Ernst Mayr defining a species as "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups." This classical definition is called the biological species concept. Under this standard definition, speciation entails the origin of such a reproductively isolated population. But does it entail anything else?

Not necessarily. Such definitions say nothing about the degree of morphological, behavioral, or genetic change that has evolved. Thus, such a definition of "species" does not necessarily imply that significant biological change has taken place between the two populations. In many cases, two populations may be termed different "species" under the biological species concept, but yet the differences between the populations are small-scale and trivial. Indeed:

  • One of the papers cited by the FAQ (Dodd, 1989) clearly states that speciation is reduced to mere reproductive isolation, "According to the biological species concept, speciation is basically a problem of reproductive isolation."1 Another paper (Shluter and Nagel, 1995) cited by the FAQ note that under this definition species are "defined by the criterion of reproductive isolation rather than morphological criteria."2
  • Yet even the notable evolutionary biologist Theodosius Dobzhansky (1972) admits that under this view, "speciation may occur without rearrangement of the genetic materials in the chromosomes" and "Reproductive isolation evidently can arise with little or no morphological differentiation."3
  • Putting these quotes, claims, and definitions together, papers cited by the FAQ admit that under the biological species concept, "speciation" does require any morphological change.

As noted, the FAQ is often cited to explicitly or implicitly claim that Darwinian evolution is capable of producing significant biological change. But the FAQ's definition of "speciation" seems contrived when used to demonstrate the grander claims of Darwinian evolution that fundamentally new biological structures, body plans, and higher taxa can evolve. Even if we do find reproductively isolated populations that document "speciation," that might provide virtually no evidence that Darwinian processes can produce new complex biological features or large-scale change. Indeed, the primary finding of this analysis is that the examples in the FAQ do not report the kind of change which shows Darwinian processes can produce fundamentally new types of organisms, new complex biological structures, or higher taxa.

What is more, the vast majority of the examples in the FAQ don't even document "speciation" under the biological species concept. One paper cited by the FAQ (Rice and Hostert, 1993) notes that "Once pre- and/or postzygotic isolation is complete, speciation has occurred."4 But in the vast majority of the instances cited by the FAQ, pre or postzygotic isolation was not complete, and thus speciation did not occur. Thus, a secondary finding of this report is that only one single paper analyzed in the entire FAQ actually reported complete reproductive isolation, and thus "speciation" under the biological species concept.

This raises an irony: the title of the FAQ is "Observed Instances of Speciation," yet the vast majority of the examples analyzed show that complete reproductive isolation was not achieved. Thus, the FAQ is overselling the evidence, not just for significant morphological change, but also for true speciation (e.g. complete reproductive isolation). If these are some of the best examples for "speciation" that evolutionists can muster, then the evidence for Darwinian evolution must be meager indeed.

Over the course a few additional articles, I will highlight some of the many examples in the FAQ where neither speciation nor large-scale biological change were observed.

For additional details, please see the full response to the TalkOrigins Speciation FAQ.

References Cited:

[1.] Diane M.B. Dodd, "Reproductive Isolation as a Consequence of Adaptive Divergence in Drosophila pseudoobscura," Evolution, Vol. 43 (6): 1308-1311 (September, 1989).

[2.] Dolph Schluter and Laura M. Nagel, "Parallel Speciation by Natural Selection," The American Naturalist, Vol. 146 (2):292-301 (August, 1995).

[3.] Theodosius Dobzhansky, "Species of Drosophila," Science, Vol. 177 (4050):664-669 (August 25, 1972).

[4.] William R. Rice and Ellen E. Hostert, "Laboratory Experiments on Speciation: What Have We Learned in 40 Years?," Evolution, Vol. 47 (6):1637-1653 (December, 1993).