Approved for Use in Texas Schools, Ken Miller's Textbook Uses Galápagos Finches to Overstate the Case for Evolution
I've been reviewing Pearson's Biology, the textbook that Ken Miller successfully submitted for adoption in Texas; see here, here, here, here, and here. On top of its other problems, the book omits crucial information about the Galápagos finches.
The textbook explains that during the famous study by Peter and Rosemary Grant the finches showed an increase in beak size, stating that "average beak size in this finch population increase dramatically. The Grants have demonstrated that natural selection takes place in wild finch populations frequently, and sometimes rapidly." (p. 472) But it fails to mention that what the Grants ultimately found was oscillating selection, where there was no net evolutionary change. The Grants found that finches with larger beaks survived better during a drought, as they were able to crack the tougher seeds that remained. When the drought ended, however, the average beak size in the finch population returned to normal.1 As Peter Grant wrote:
Effects of the droughts of 1977 and 1982 were approximately offset by selection in the opposite direction -- toward smaller body size -- in 1984-85. A relative scarcity of large seeds, together with an ample supply of small ones, favored small finches. Because the food supply on this island changes in composition and size from year to year, the optimal beak form for a finch is shifting in position, and the population, subjected to natural selection, is oscillating back and forth with every shift. Whether or not there is a net directional arrow through the oscillations, is unclear and could be determined by a much longer study.2
Pearson's textbook omits mention of this. Instead, Figure 16-18 in the textbook (p. 473) only shows beak size in the Galápagos finches increasing. This misrepresents the Grants' findings.
Additionally, on page 550 the textbook cites the Galápagos finches as an example of adaptive radiation, stating, "Galápagos finches and Hawaiian honeycreepers also experienced adaptive radiations." (p. 550) However, aside from small differences in beak shape, size, and feeding habits, the finches are highly similar. They are so similar that it can be quite difficult to tell the finch species apart. In his Pulitzer Prize-winning book The Beak of the Finch, Jonathan Weiner compares the largest and smallest species of Galápagos ground finches and remarks that they are "almost indistinguishable."3
Likewise, a paper in BioScience noted that after a full 14 million years of evolution, the finches remain highly similar and even "retain the ability to interbreed and produce viable, fertile hybrids."4 The small-scale differences between the finch species do not demonstrate that all living organisms are related through descent with modification. Rather, the finches show that after millions of years of evolution, very little has changed within a group of highly similar finches. They demonstrate microevolution, but cannot necessarily be extrapolated to demonstrate macroevolution.
Pearson's textbook thus omits key information about the finches -- the lack of net evolution in the Grants' study, and the birds' ability to interbreed -- information that undermines claims made in the text. Failure to discuss this counterevidence misleads readers about the nature of the subject of evolution. On that topic, Miller's book is seriously flawed. As I have shown in this series, Texas students, and others across the country, deserve better.
[1.] H. Lisle Gibbs and Peter R. Grant, "Oscillating selection on Darwin's finches," Nature, Vol. 327: 511-513 (June 11, 1987).
[2.] Peter R. Grant, "Natural Selection and Darwin's Finches," Scientific American, pp. 82-82 (October, 1991).
[3.] Jonathan Weiner, The Beak of the Finch, p.43 (Vintage Books, 1994).
[4.] Jeffrey Podos and Stephen Nowicki, "Beaks, Adaptation, and Vocal Evolution in Darwin's Finches," BioScience, Vol. 54(6):501-510 (June 2004).