You’ve heard about the elephant in the room—but what if the elephant is a whale?
I distinctly remember feeling uneasiness when I came upon a blue whale skeleton hanging from the ceiling in the Museum of Natural History in London. It wasn’t the skeleton’s massive size that caused my disquiet—it was the small pelvic and hind limb bones suspended in midair, just below the vertebral column, near the skeleton’s posterior end (figure 1). These bones are easy to miss, but I found them impossible to ignore.
Figure 1. Skeleton of Baleen Whale.
Image credit: Azcolvin429 (Wikimedia/Creative Commons)
Evolutionary biologists like to point to vestigial structures—such as the pelvis and hind limbs of whales and dolphins (cetaceans)—as compelling evidence for biological evolution. If you’ve taken a biology course or seen television specials on evolution, it’s likely you’ve heard people discuss the whale pelvis and explain why it serves as evidence for common descent. But new work by researchers from the University of Southern California (USC) and the Natural History Museum (NHM) of Los Angeles County has provided a way for creationists and intelligent design (ID) proponents to explain cetaceans’ diminutive pelvis and hind limbs.1
Whales first appear in the fossil record around 50 million years ago. Some evolutionary biologists think these aquatic mammals evolved from Pakicetus, a wolf-like carnivore linked to whales based partially on the structure of its inner ear bone. Indohyus, a deer-like creature dating around 48 million years old, has also been linked to whales based on shared anatomical features. (For more details, listen to the December 20, 2007 episode of Science News Flash.)
Paleontologists have discovered a number of putative transitional intermediates that led to the emergence of ancient whales. These fossils date to around 45 to 50 million years in age. According to the evolutionary paradigm, as these intermediate forms transitioned from life on the land to life in the oceans, the fore limbs evolved into flippers. Meanwhile, the hind limbs and pelvis became dramatically reduced in size with lost function. In other words, they became vestigial.
Evolutionary biologists view vestigial structures as compelling evidence for evolution, because they are also homologous structures. Vestigial structures are rudimentary body parts that are smaller and simpler than the corresponding features possessed by the other members of a biological group. In this case, the vestigial whales pelvis and hind limbs are homologous to the pelvis and hind limbs of all other mammals.
Evolutionary biologists believe that vestigial structures were fully functional at one time, but degenerated over the course of many generations because the organisms no longer needed them to survive in an ever-changing environment. From an evolutionary standpoint, fully functional versions of these structures existed in the ancestral species. If needed for survival, the structures’ form and function may be retained (possibly modified) in some of the evolutionary lineages derived from the ancestral species, but, if no longer required, the structures become diminished (and even lost) in other lineages.
Do Vestigial Structures Support Evolution?
Evolutionary biologists believe the whale flipper and other vertebrate fore limbs (such as the human hand, a bat wing, a horse hoof, etc.) demonstrate shared ancestry. They reason that evolutionary forces independently modified the vertebrate fore limb possessed by land vertebrates’ common ancestor. This led to disparate structures with a wide range of distinct functions as the various lineages diverged from the common ancestor. Yet these structures retained their basic design. To put it another way, the homologous structures of the various vertebrate fore limbs document evolutionary history.
An alternate explanation for homologous structures does exist. Following in the footsteps of eminent biologist Sir Richard Owen, I would argue that homologous structures reflect common design, not common descent. In this scheme, the common ancestor is replaced by a design archetype that resides in the Creator’s mind and is utilized in a variety of forms and functions.
This is where vestigial structures, such as the whale pelvis and hind limbs, enter the debate. Evolutionary biologists argue that common descent offers a better explanation than common design because it readily accounts for vestigial features that are also homologous structures.2 However, recent work by the USC and MNH scientists indicates that the whale pelvis isn’t vestigial. They demonstrate that it serves as an attachment point for muscles that both male and female cetaceans need to reproduce. So, from an evolutionary perspective, the whale and dolphin pelvis appears to be under the influence of selection—a sure indication of function.
According to Matthew Dean, one of the authors of the study, “Everyone’s always assumed that if you gave whales and dolphins a few more million years of evolution, the pelvic bones would disappear. But it appears that’s not the case.”3
This is not the first time scientists have discovered utility for vestigial structures. As Dean also noted, “Our research really changes the way we think about evolution of whale pelvic bones in particular, but more generally about structures we call ‘vestigial.’ As a parallel, we are now learning that our appendix is actually quite important in several immune processes, not a functionally useless structure.”4
Evolutionary biologists will argue that this insight doesn’t diminish the case for biological evolution one bit. They will maintain that the whale pelvis is a homologous structure, even if it isn’t vestigial, and therefore supports common ancestry. For creationists and ID adherents, on the other hand, this insight is significant. The whale pelvis’ functional role makes it reasonable to argue that this structure is the expression of an archetypical design—the work of a Creator. If the whale pelvis were truly vestigial, this argument would be harder to make.
Over the last several years RTB scholars have written a number of articles and recorded several podcasts on vestigial structures that, in fact, are functional.