Back to School to Learn about the "Darwin's Finches" Icon of Evolution
With students returning to school now, it's worth mentioning a delightful book, published last year, by University of Texas, Austin historian Alberto A. Martinez: Science Secrets: The Truth about Darwin's Finches, Einstein's Wife, and Other Myths. Science Secrets takes on a number of well-established scientific myths, including some that seem stubbornly ensconced in science textbooks.
One of these is the idea that the Galápagos finches -- known as "Darwin's finches" -- were critical to the development of Darwin's ideas about evolution. Martinez debunks this myth:
Many old books claim that when Charles Darwin visited the Galápagos Islands, he was inspired to think about evolution by seeing variations in finches' beaks. ... Allegedly, he found that each species of finch belonged to a particular island and had developed distinct feeding habits that matched their evolving beaks, for cracking small or big seeds or for eating insects. That's what many people still think, and so, one of the most widely reproduced pictures in history is that of Darwin's finches.Martinez goes on to observe that "Textbooks decorated by pictures of finches echoed such claims" (p. 96). But if you read ENV regularly, you knew this already. We documented recent textbooks that make false claims about the Galápagos finches in our "Evaluation of 22 Recent Biology Textbooks and Their Use of Selected Icons of Evolution," released last year. For example:
However, in sterling historical studies, Frank J. Sulloway of Harvard University showed that, really, Darwin was hardly influenced by finches and scarcely observed their feeding habits. He did not correlate their diets and beaks; in fact, Darwin collected too few specimens to determine whether any finch species was unique to each island. He did not even keep track of where he picked up every specimen. Really, no finch species was unique to any one island. Unfortunately, some teachers and writers remain unaware of Sulloway's historical findings.
(Alberto A. Martinez, Science Secrets: The Truth about Darwin's Finches, Einstein's Wife, and Other Myths, pp. 95-96 (University of Pittsburgh Press, 2011).)
- BSCS Biology: A Molecular Approach (Glencoe/McGraw Hill, 2006) states: "On the Galápagos Islands, which Darwin visited during his travels, some members of the same finch species have short, thick beaks while others have longer, thinner beaks. On the basis of these observations, Darwin concluded that some variations would help members of a species survive in a particular environment, whereas other variations would not be helpful." (pp. 10-11)
- Sylvia S. Mader, Essentials of Biology (McGraw Hill, 2007) states: "One of the best examples of speciation through adaptive radiation is provided by the finches on the Galápagos Islands, which are often called Darwin's finches because Darwin first recognized their significance as an example of how evolution works." (p. 251)
- Sylvia S. Mader, Biology (McGraw Hill, 10th ed., 2010) is even worse, stating: "These birds would eventually play a major role in his thoughts about geographic isolation" and "Darwin had formed his natural selection hypothesis by observing the distribution of tortoises and finches on the Galápagos Islands." (pp. 270, 275)
- Kenneth R. Miller and Joseph Levine's Biology (Pearson, 2010) is also quite bad, stating:
Darwin noticed several types of small brown birds on the islands with beaks of different shapes. He thought that some were wrens, some were warblers, and some were blackbirds. ... the little brown birds that Darwin thought were wrens, warblers, and blackbirds were actually all species of finches! They, too, were found nowhere else, though they resembled a South American finch species ... Darwin was stunned by these discoveries. He began to wonder whether different Galápagos species might have evolved from South American ancestors. He spent years filling notebooks with ideas about species and evolution. ... Once Darwin learned that the birds were all finches, he hypothesized that they had descended from a common ancestor. Darwin noted that several finch species have beaks of very different sizes and shapes. Each species uses its beak like a specialized tool to pick up and handle its food... Darwin proposed that natural selection had shaped the beaks of different bird populations as they became adapted to eat different foods. (pp. 452-453, 471-472)
To return to the myth about finches, we can summarize that old story as follows: While visiting the Galápagos Islands, Charles Darwin noticed that various species of finches had beaks of different shapes and sizes. Observing their eating habits, he noticed that the shapes of their beaks corresponded to their diets. He also noticed that some species were distinct to some islands. Hence he inferred that the various species were related: they were descended from common ancestors that had populated the islands and had adapted variously to the distinct island conditions. Species evolved.Jonathan Wells of course wrote very much the same thing in Icons of Evolution. He devoted an entire chapter to the icon of Darwin's finches, and summarized problems with this textbook myth as follows:
The short story works because it fits in the space allotted by a science textbook. And it works because, as Sulloway argued, it fits into the form of a classic journey of discovery: man departs from home on a bold adventure, encounters and overcomes hardships, and returns with a deep truth. But the story is false... (p. 117)
The Galápagos finches did not inspire Darwin with the idea of evolution, and oscillating natural selection on their beaks produces no observable net change. (Icons of Evolution, p. 260)It looks, in other words, like Jonathan Wells has been vindicated once again. It would be nice to think that someday biology textbooks will be amended accordingly.