Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education ARCHAEOPTERYX ple of how fossils are important for showing transitional features of evolution, and how the ARCHAEOPTERYX: THE FOSSIL fossil record is good evidence that evolution ontrary to Wells’s subtitle, has occurred. Archaeopteryx is not a “missing link.” WELLS MISSES MORE CThe term “missing link” is an outdated THAN THE LINKS term that does not accurately reflect the way ells objects to textbook treatments biologists and paleontologists think about fos- of Archaeopteryx as a transitional sils. We prefer not to talk about “missing Wform or as an “ancestor” of birds. links” or “intermediate forms,” but rather Wells wants textbooks to say that intermediate features. Archaeopteryx has fea- Archaeopteryx was not an “ancestor” because tures intermediate between those of living modern birds are not descended from it and birds and ancient reptiles; along with many that its transitional status is “controversial.” other fossils, it preserves ancestral features Wells claims that Archaeopteryx has been while it shows descendant novelties. “quietly shelved” by paleontologists and that Archaeopteryx retains the ancestral “reptilian” the search for a “missing link” between features of a long bony tail, clawed hands, dinosaurs and birds goes hopelessly on “as teeth, and many others. It also has the derived though Archaeopteryx had never been found” “avian” features of feathers and powered (Wells, 2000:138). Paleontologists would find flight. Archaeopteryx, along with other this surprising. By making such claims, Wells dinosaur fossils, shows the evolution of avian exposes the depths of his ignorance of phylo- features and flight. These fossils show that genetic methodology, paleontology, and avian many features thought of as unique to a certain evolution. group of animals were also shared by some of Wells is clearly confused by Archaeopteryx, their ancestors; this helps paleontologists to “transitional forms,” and ancestors. First of all, reconstruct the evolutionary history of living Wells asserts that Archaeopteryx is no longer animals. When many fossils are looked at in considered a transitional form or an “ances- their genealogical context, they blur the lines tor.” Wells is correct, but only in a specialized between the normally recognized taxonomic sense, not appropriate in the context of his groups (most of which were based originally generalized discussion. We cannot — and do only on living forms). Archaeopteryx is fre- not — say for certain that the animal that we quently used for pedagogical purposes because call Archaeopteryx was actually genetically it is easy to recognize its mixture of “bird” and transitional to living birds, or that it was a “reptile” features and because it played an his- direct genetic ancestor of living birds. torical role in helping to cement Darwin’s the- However, in a less strict sense (that appropriate ory (it was discovered 2 years after publication to Wells’s discussion), Archaeopteryx has a of the Origin). Textbook authors like great many transitional features between living Archaeopteryx for these reasons and often birds and Mesozoic dinosaurs: if it was not a illustrate their discussions with pictures of the direct ancestor, it was surely a close collateral Berlin specimen, one of the most beautiful fos- ancestor (see below). sils ever discovered, and remarkably complete. Second, there is no such thing as a “missing Textbooks also use Archaeopteryx as an exam- link,” and paleontologists are not looking for 41 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education them. Paleontologists collect, survey, and rect. Archaeopteryx has no features that would reconstruct past forms of life. Some of these actually disbar it from being a direct ancestor fossil organisms have features that illustrate of living birds. Whether it was a direct ances- the path evolution took to reach the forms we tor of today’s birds or not is irrelevant: see today. We can think of these organisms as Archaeopteryx exhibits unique features of the showing transitional or ancestral features. last ancestor it shared with birds, so, regardless Paleontologists are also not looking for ances- whether it is a lineal ancestor, it still preserves tors, but rather features of ancestors. features that indicate what the last ancestor of Paleontologists distinguish between lineal and Archaeopteryx and birds may have been like. collateral ancestors. Lineal ancestors are those In other words, Archaeopteryx has many fea- that are directly ancestral to living organisms: tures intermediate between those of its your lineal ancestors are your father and moth- dinosaurian ancestors and its avian descen- er, grandfathers and grandmothers, and so on. dants, which is exactly what would be predict- Collateral ancestors are those organisms that ed by evolution. No amount of stridency on share an ancestor with living organisms: your Wells’s part can change that. collateral ancestors are your uncles, great- When paleontologists reconstruct relation- uncles, cousins, second cousins, and so on. ships of living and fossil organisms, they use Paleontologists do not claim to be able to iden- the features of both living and fossil organ- tify lineal ancestors. Without observational or isms. This allows them to reconstruct the fea- genetic evidence, how could you ever know tures of the ancestors and get a pretty good pic- that a fossil organism left any offspring? It is ture of what the ancestors were like. not the ancestry that is important to paleontol- Phylogenetic systematics, commonly called ogists, but rather the ability to reconstruct the “cladistics,” is the method that nearly all biol- features of those ancestors. This is a powerful ogists use to determine relationships, whether and important concept, one completely lost on they work on dinosaurs or dinoflagellates, and Wells. whether they use molecules or morphology. Its To illustrate this powerful approach, let’s simplicity, objectivity, testability, repeatability, say you wanted to know something about your utility, and firm rooting in the principle of own ancestors. If you knew your ancestors descent has led to its near-universal applica- came from a certain small village in France in tion. Contrary to Wells’s characterization, the 1600s, you could return to that village and, cladistics is not a search for “missing links” or even if you can’t locate their graves, you might direct ancestors, but for shared evolutionary find those of many of their contemporaries in features. The basic idea behind cladistics is the churchyard. A collection of artifacts from that when novel features arise, they are passed any of those people would give you a perfect- on to descendents. Therefore, these “derived ly adequate idea of the characteristics, culture, features” should be more informative in recon- possessions, and daily life of your direct structing relationships than those that are pres- ancestors (Padian and Angielczyk, 1999). ent across a larger group. For example, if a Using similar methods for similar reasons, population of animals evolve stripes on their paleontologists try to uncover features of backs and all their descendants continue to ancestors, not the ancestors themselves. sport stripes, then all the members of that Even Wells’s claim that paleontologists do species that have stripes are probably more not think Archaeopteryx is “ancestral” is incor- closely related to each other than they are to 42 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education those without stripes. It is that simple, yet ing” the evidence, stating that the supposed Wells’s discussion of cladistics reveals that he “ancestors” of Archaeopteryx are millions of either does not grasp the method or has no years younger. First of all, none of these more interest in explaining it properly. “recent” avian-like dinosaurs thought to be In the nearly two pages devoted by Wells to closely related to Archaeopteryx (e.g., a discussion of cladistics (Wells, 2000:118– troodontids and dromaeosaurs) are considered 119), he states that cladistics is based on over- “ancestors”; rather, they retain ancestral fea- all similarity. Yet as stated above, cladistics is tures that show us what the ancestors of not based on mere similarity, but instead Archaeopteryx were like. Here again Wells focuses on a special kind of similarity — fea- mistakes lineal for collateral ancestry. Second, tures that are derived, or evolutionary novel- the statement that there are no fossils of these ties. Evolutionary novelties help to show rela- close cousins of Archaeopteryx until “millions tionships and thus are “phylogenetically of years” later is false. Fossils of non-avian informative.” In contrast, similarities that are maniraptor dinosaurs, which are closely relat- not evolutionary novelties are “ancestral” fea- ed to the ancestors of Archaeopteryx, have tures and are not phylogenetically informative. been found in rocks dating to the same age as For example, a derived feature of primates is those in which Archaeopteryx has been found an opposable thumb; this feature is phyloge- (Jensen and Padian, 1989); this discovery was netically informative because it allows us to reported over 10 years ago. Wells apparently group all primates together to the exclusion of has not done his homework very well. other mammals. On the other hand, a five-fin- Despite Wells’s claims to the contrary, gered hand is an ancestral feature and not phy- Archaeopteryx is still an important contributor logenetically informative because we would to our knowledge of transitional features, and not group all animals possessing a five-fin- it clearly shows the dinosaurian ancestry of gered hand together to the exclusion of those birds (Figure 12). To confirm this, all one has that do not. For example, we do not propose to do is peruse any piece of literature on the that all five-fingered mammals are more close- origin of birds.