Frequently asked questions about evolution
The Discovery Institute has been supplying parents and students with a ready-made list of questions that creationists believe somehow cast doubt on the theory of evolution. These questions are wholly explainable and do NOT damage the theory of evolution in any way. Nonetheless, if a teacher does not have detailed knowledge of these topics (which is totally understandable), they may have difficulty explaining them to their students. For this reason, we have outlined the questions (in blue type) and have supplied short answers to these questions (in black type). One can see that many of these Discovery Institute questions are also replicated in Ohio's 10th grade "Critique of Evolution" lesson plan, which underscores the Discovery Institute's involvement with the creation of this lesson plan.
An excellent resource for many of these types of questions can be found at TalkOrigins.org and Evolutionhappens.net, which are specifically aimed at deciphering the creationism/evolution debate.
1) The origins of life. Why do textbooks claim that the 1953 Miller-Urey experiment shows how life's building blocks may have formed on Earth - when conditions on the early Earth were probably nothing like those used in the experiment, and the origin of life remains a mystery?
2) Darwin's tree of life. Why don't textbooks discuss the "Cambrian explosion," in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor - thus contradicting the evolutionary tree of life?
Answer: The Cambrian Explosion is often cited as an example of a ‘sudden appearance’ of biological forms. However, the fossil record extends back billions of years before the Cambrian to the Proterozoic, where we have records of eukaryotic bacteria. Even 93 million years before the Cambrian is a fauna known as the Ediacarian fauna. Many of the major phyla can be recognized in the Ediacarian, but as soft bodied organisms. The only ‘explosion’ that can be seen in the Cambrian is the development of hard parts (e.g., shells and other exoskeletons) for these previously soft-bodied organisms. Because these skeletal elements are preserved more readily, they record their existence more easily. Therefore, the supposed “Cambrian explosion” (which some have used to indicate that species do not evolve via small accumulated changes over long time periods) is likely an artifact of the way animals are fossilized (i.e., hard parts are more easily preserved than soft parts) rather being a sign that numerous groups underwent a period of intense speciation, or "suddenly appeared" as if they were "created by an intelligence."
3) Vertebrate embryos. Why do textbooks use drawings of similarities in vertebrate embryos as evidence for common ancestry - even though biologists have known for over a century that vertebrate embryos are not most similar in their early stages, and the drawings are faked?
Many vertebrate embryos are “similar” at one or several of their early stages of development, commonly referred to as the “von Baer’s laws”. It’s true that they don’t look as similar as depicted in the drawings, but they all have common structures such as: three germ layers, notochord, and gill slits. The key here is that the vertebrate embryos do not necessarily look similar, but they possess similar structures (now we know that they have similar key regulatory genes controlling the formation of these structures).
The following are the four useful generalizations of von Baer:
- The general features of a large group of animals appear earlier in development than do the specialized features of a small group.
- Less general characters develop from the more general ones, until finally the most specialized characters appear.
- The embryos of a given species, instead of passing through the adult stages of lower animals, departs more and more from them.
- Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo.
In evolutionary biology, evidence of common or shared ancestry comes from analyses of the characteristics of organisms. In general, shared characteristics can be used to reconstruct genealogical relationships: organisms which share many specific characteristics are usually more closely related to one another than they are to organisms which don’t display the same characteristics. Two rather famous developmental biologists who worked in the 1800’s (Ernst Haeckel and Carl von Baer) are often associated (But it was Haeckel’s thesis, not von Baer’s) with an idea known as the “Biogenetic Law,” which holds that embryonic development in vertebrates parallels phylogenetic history. Haeckel’s work especially, was motivated by a desire to place developmental biology within an explicit evolutionary framework. Haeckel based the formulation of his ‘law’ on a detailed morphological analysis of various vertebrate embryos (which he captured with famous and oft cited drawings) at different stages of development. There are at least two misconceptions among biologists and non-biologists alike about Haeckel’s work. First, some have claimed that Haeckel faked his drawings to prove his law. Briefly, there is no definitive evidence that Haeckel ‘faked’ his drawings, but inaccuracies had been identified and even acknowledged by Haeckel himself (criticisms of the some of the details of drawings date back to 1868!). Second, the biogenetic law is often strictly, though mistakenly, interpreted as ‘ontogeny recapitulates phylogeny.’ However, such a view is arguably much more simplistic than that even held by Haeckel, and certainly has not been in the main stream of developmental or evolutionary biological thinking at least sine the publication of a major treatise on evolutionary development published by S.J. Gould, in 1977. It is now widely appreciated that the patterns noticed by Haeckel and elaborated on by many developmental biologists since, are merely another source of evidence of how closely-related organisms share defining characteristics at multiple points in their development. This is a basic fact of evolution. It is not a principle that is made or broken by the analysis of Haeckel, nor is there a threat to the theory of evolution stemming from any misunderstandings of Haeckel’s observations or analysis. Similarities in the developmental stages of vertebrates complement similarities seen in adult stages, together providing evidence of evolutionary relationships.
4) The archaeopteryx. Why do textbooks portray this fossil as the missing link between dinosaurs and modern birds - even though modern birds are probably not descended from it, and its supposed ancestors do not appear until millions of years after it?
Answer: A commonly used example of a “challenge” to evolution by natural selection is the supposed “transitional” species that links dinosaurs to birds: Archaeopteryx. Archaeopteryx is not the direct ancestor to modern birds. At best, it is a side branch to the rest of the lineage. At one time, when we had very few bird fossils (birds typically do not preserve well in the fossil record because they do not live in water), paleontologists thought that it might be the link between dinosaurs and modern birds. However, the last 10-15 years of fossil discoveries of ancient birds, mostly in China, has brought a new and clearer way of understanding bird evolution. It is not a ladder-like pattern, but a bush-like pattern, with many branches. What we do know is that birds are ancestrally related to dinosaurs, and many paleontologists argue that birds are part of the dinosaur evolutionary tree that remains with us to this day.
5) Peppered moths. Why do textbooks use pictures of peppered moths camouflaged on tree trunks as evidence for natural selection - when biologists have known since the 1980s that the moths don't normally rest on tree trunks, and all the pictures have been staged?
Answer: The assertion that ‘moths don't normally rest on tree trunks,’ is patently untrue: the best estimate is that peppered moths rest on tree trunks about 25% of the time they are at rest. The remainder of their time, they are on other parts of the tree. Although the original study used a comparison of moths on tree trunks, the findings are not confined to moths that only rest on tree trunks. The basic idea was that the habitat for these moths were changing due to human impact (industrial air pollution that was blackening trees), and that this change had selected for a darker (melanic) color mutant of these moths. The effects of pollution affected BOTH tree trunks but also other parts of trees on which moths spend the balance of their time (and on which moths would also be subject to predation).
Since this pioneering study, more recent studies of the peppered moths in other parts of its geographic range subject to the darkening effects of pollution have also shown similar changes in the frequencies of light and dark morphs over time. Additionally, 30 other studies of other moth species have shown the same response of increased melanism in industrialized regions (Grant, Bruce, 1999: "Fine Tuning the Peppered Moth," Evolution 53: 980-984).
The Discovery Institute is picking up on a book written by a journalist (J. Hooper) that made some unscientific assertions of fraud in the original studies of the peppered moth. These assertions have been shown to be false, but still the Discovery Institute clings to this book to obfuscate the truth (a recurring theme from this group).
6) Darwin's finches. Why do textbooks claim that beak changes in Galapagos finches during a severe drought can explain the origin of species by natural selection - even though the changes were reversed after the drought ended, and no net evolution occurred?