This Is Brad Gessell Speaking: Evolutionary support for whales

Throughout history, many people have proposed bold new theories that transcend the thinking of the day. As time progresses, the proposed theories will either be justified with further evidence, or discarded because of further evidence. The theory of evolution is a great example of a theory that has been justified by further evidence, and will help us understand more about the way life works.

When people think of aquatic animals and evolution, it is natural for them to think of fish “walking out of the water” to become a land animal. The college textbook Strickberger’s Evolution even has a flip-book type illustration throughout the text of an animal leaving the water and walking on land. Whales, however, seem to have taken a different route. There is strong evidence that whales are an evolved species from a land animal to a purely aquatic one.

In order for a species to evolve from a land dwelling creature to a solely aquatic mammal, sizeable changes must occur over time. These changes come slowly as natural selection chooses what traits are beneficial for survival and reproduction, and those traits are passed on to offspring one by one, until new creatures are formed. “By such logic it is easy to imagine a slightly aquatic mink- or bearlike ancestor giving rise to a more aquatic otterlike stage, followed by a seal-like pinniped stage, until finally whales became fully aquatic as they are today” (Gingerich, 2003, p. 429). As natural selection ran its course, the whale “lost its legs, and all of its vital systems became adapted to a marine existence -- the reverse of what happened millions of years previously, when the first animals crawled out of the sea onto land” (WGBH, 2001, p. 1). The discovery and research of many forms of intermediary fossils show the progression of early whale ancestors.

Throughout the fossil record, it is evident that body parts and body shape have changed over time. The features that have shown evidence of change include the jaw and teeth, muzzle, extremities, and other bone structures.

In the earliest fossils on record (Sinonyx), the teeth were differentiated similar to today’s mammals. In a fossil dated 8 million years later, the teeth had already begun to specialize into the type we are familiar with in today’s whales. “The upper and lower molars, which have multiple cusps, are still similar to those of Sinonyx, but the premolars have become simple triangular teeth composed of a single cusp serrated on its front and back edges” (Sutera, 2001, p. 1). Throughout the remainder of the whale lineage, the teeth become even more specialized until there is a “reduced differentiation among the teeth” (Sutera, 2001, p. 1). In today’s whales, the teeth “are always simple cones or pegs; they are not differentiated by region or function as teeth are in other mammals” (Sutera, 2001, p. 1).

Another important characteristic that has evolved throughout the ages is the positioning of the ear in the skull. Regarding extant ear positioning in whales, “it is extensively modified for directional hearing underwater.” 52 million years ago, “the ear region [was] intermediate between that of terrestrial and fully aquatic animals” (WGBH, 2001, p. 1).

One of the most interesting features of ancestral whales that have since been lost is the limbs. There is ample evidence (in modern whales and in whale predecessors) to show that there were fully usable, working limbs. According to Hall and Hallgrimsson, a vestigial organ is defined as “Organs or structures that appear to be small and functionless but can be shown to be homologous with ancestral organs and structures that were larger and functional” (Hall and Hallgrimsson, 2009, p. 733). Due to natural selection and changing environments, some features in creatures are no longer necessary.

Consequently, “obsolete structures would tend to diminish, showing only traces of their former size and function” (Hall and Hallgrimsson, 2009, p. 46). Whales possess vestigial organs in the form of a pelvis and leg bones. However, the “hind limbs and pelvis are extremely small and do not normally extend out of the body wall of the animal” (Waggoner, 2001, p. 1). Various types of whales have similar anatomies.

To solidify the argument of whale evolution, whales possess muscles that would move their external ears if they had any. “All whales have a number of small muscles devoted to nonexistent external ears, which are apparently a vestige of a time when they were able to move their ears - a behavior typically used by land animals for directional hearing” (Sutera, 2001, p. 1).

The significance of these vestigial organs as further evidence of natural selection and evolution is great, because “an organism adapting to a new environment usually carries along some previously evolved structures that are no longer necessary“ (Hall and Hallgrimsson, 2009, p. 46). At some point in the history of these organisms, active, functional hind limbs were no longer necessary, so the pelvic and femur bones were simply “carried along”, as Hall and Hallgrimsson state.

The evidence conclusively shows that early on in whale history, these beasts were once land-dwelling creatures which evolved into the animals we know them as today. As time goes on, we will learn more and more about why and how this happened, as well as see further speciation amongst populations.

Gingerich, Philip D. 2003. Land-to-sea transition in early whales: evolution of Eocene Archaeoceti (Cetacea) in relation to skeletal proportions and locomotion of living semiaquatic mammals. Paleobiology 29(3)429-454. http://www.bioone.org/doi/pdf/10.1666/0094-8373%282003%29029%3C0429%3ALTIEWE%3E2.0.CO%3B2