Closely related to the phenomenon of repeatable evolution is convergence. Convergence refers to the widespread tendency in nature of unrelated organisms to possess nearly identical anatomical and physiological characteristics.1 The wings of birds and bats is one textbook example of convergence. Birds and bats are unrelated organisms, with birds belonging to the class Aves and bats to the class Mammalia. Though superficially similar, the wing structures of birds and bats are fundamentally different. Another common example of convergence—one in which the fundamental structural differences are not so obvious—is the remarkable anatomical similarity shared by the modern placental wolf and the extinct Tasmanian wolf.2
Both the creation and evolutionary paradigms offer an explanation for convergence. Creationists view convergence as the intelligent activity of a single Creator who employs a common set of solutions to address a common set of problems facing unrelated organisms in their quest for survival. Evolutionists assert that convergence results when unrelated organisms encounter nearly identical selection forces (environmental, competitive, and predatory pressures). Natural selection then channels the random variations believed to be responsible for evolutionary change along similar pathways to produce similar features in unrelated organisms.3
Since both the creation and evolutionary frameworks attempt to explain biological convergence, an analysis of this feature of nature can be used to evaluate the two paradigms. When critically assessed, the evolutionary paradigm is found to be woefully inadequate when accounting for all the facets of biological convergence. On the other hand, biological convergence is readily explained by an origins model that evokes a single Creator.
One of the challenges that convergence creates for the evolutionary paradigm is the frequency with which it occurs throughout life’s history. Convergence is a common characteristic of life. This commonness makes little sense in light of evolutionary theory. If evolution is indeed responsible for the diversity of life, one would expect convergence to be extremely rare. The mechanism that drives the evolutionary process consists of a large number of unpredictable, chance events that occur one after another. Given this mechanism and the complexity and fine-tuning of biological systems, it seems improbable that disparate evolutionary pathways would ever lead to the same biological feature.4
Two remarkable examples of complex biological features recently recognized as being convergent are bat echolocation (the ability of an organism to orient itself based on perceiving reflections of sound it emits) and parrot, songbird, and hummingbird forebrain structure. A recent DNA sequence analysis has just confirmed two earlier studies that, from an evolutionary perspective, requires echolocation in bats to have evolved independently in two separate groups (microchiroptera and megachiroptera).5-7 This study, along with previous analyses also indicate that the strikingly similar limb structures of bats and flying lemurs used for flying, likewise, must have evolved independently, when the data is interpreted from an evolutionary perspective.
Another recent study, employing behavioral differences in gene expression in brain tissue, has demonstrated that the brain structure of hummingbirds, songbirds, and parrots responsible for vocal learning (the ability to “learn” vocalizations by imitation rather than by instinct) is essentially identical.8-9 This is surprising, since these three birds are unrelated to one another. That is, the seven distinct structures in the forebrain of these three groups of birds that are responsible for vocal learning are convergent. From an evolutionary perspective, these structures must have evolved independently of one another on three separate occasions.
It is difficult to accept, even when biased towards naturalism, that the complex structures involved in bat echolocation, bat and lemur flight, and bird vocal learning could have emerged strictly through random events. However, the remarkable convergence just described would be expected if a single Creator was responsible for creating bats, lemurs, parrots, songbirds, and hummingbirds.
Even more challenging for the evolutionist are the cases in which convergence occurs in organisms from radically different environments. Under these circumstances, the forces that comprise natural selection must be different by definition. The classic example of this type of convergence is found in the eye structure of the cephalopods (nautili, cuttlefish, squids, and octopods).10 Their similarity to vertebrate eyes is remarkable from an evolutionary perspective, given that 1) mollusks, which include cephalopods, are classified as a member of a fundamentally different group (lophotrochozoan) than vertebrates (deuterostomes)11; and 2) the selective forces that would have shaped the formation of both the cephalopod eye and vertebrate eye must have been quite different. Evolution would have required an aquatic environment for the cephalopods and a primarily terrestrial environment for the vertebrates.
An even more remarkable example of convergence occurring in aquatic and terrestrial environments can be seen in the sandlance (fish) and chameleon (reptile), respectively. Recent experiments have uncovered an extraordinary similarity in the visual systems and behavior for these two creatures.12-15 Both the chameleon and the sandlance move their eyes independent of one another in a jerky manner, rather than in concert. While one eye is in motion the other eye is motionless. Moreover, both animals use the cornea of the eye to focus on objects. All other reptiles and fish use the lens of the eye to focus images on the retina. The chameleon and sandlance both rely on a specialized muscle (the cornealis muscle) to adjust the focusing of the cornea. The chameleon determines depth perception using a single eye. Scientists believe the sandlance also determines depth perception in this manner. Both the sandlance and the chameleon have skin coverings over their eyes to prevent them from being conspicuous to both predators and prey. The feeding behavior of both animals is also the same. The trajectory that the chameleon tongue takes when attacking its prey is the same as that taken by the sandlance when it lunges for its prey. (The sandlance buries itself in sand beds with its eyes above the surface of the sand and waits for tiny crustaceans to pass by.)
The words of the team of researchers who were among the first to discover this convergence are compelling: “When faced with a beautifully coordinated optical system such as this, it is a challenge to provide an explanation for the convergence of so many different finely-tuned mechanisms.”16
These examples highlight the difficulty that convergence creates for the evolutionary paradigm. No known evolutionary mechanism can account for the nature of biological convergence. Convergence has been far too common throughout life’s history, has involved exceedingly complex structures, and has occurred in situations in which the forces of natural selection have been vastly different. Biological convergence is an important component in the argument that life, throughout Earth’s history, is a result of the supernatural activity of a Creator.
- Monroe W. Strickberger, Evolution, 3rd ed., (Sunberg, MA: Jones and Bartlett Publishers, 2000), 632; 637.
- Mark Ridley, Evolution, 2nd ed. (Cambridge, MA: Blackwell Science, 1996), 470-72.
- Strickberger, 632; 637.
- Kurt Wise, “The Origin of Life’s Major Groups,” in The Creation Hypothesis: Scientific Evidence for an Intelligent Designer, J.P. Moreland, ed. (Downers Grove, IL: InterVarsity Press, 1994), 212-15.
- Emma C. Teeling et al., “Molecular Evidence Regarding the Origin of Echolocation and Flight in Bats,” Nature 403 (2000): 188-92.
- Dorothy E. Pumo et al., “Complete Mitochondrial Genome of a Neotropical Fruit Bat, Artibues Jamaicensis, and a New Hypothesis of the Relationships of Bats to Other Eutherian Mammals,” Journal of Molecular Evolution 47 (1998): 709-17.
- James M. Hutcheon et al., “Base Compositional Biases and the Bat Problem III. The Question of Microchiropteran Monophyly,” Philosophical Transaction of the Royal Society of LondonB 353 (1998): 607-17.
- Erich D. Jarvis et al., “Behaviorally Driven Gene Expression Reveals Song Nuclei in Hummingbird Brain,” Nature 406 (2000): 628-32.
- Annette Heist, “Singing in the Brain,” Natural History, October (2000): 14-16.
- Robert D. Barnes, Invertebrate Zoology, 3rd ed., (Philadelphia, PA: W.B. Sanders Company, 1974), 424-27.
- Anna Marie A. Aquinaldo and James A. Lake, “Evolution of Multicellular Animals,” American Zoologist 38 (1998): 878-87.
- Mandyam V. Srinivasan, “When One Eye Is Better Than Two,” Nature 399 (1999): 305-07.
- J.D. Pettigrew and S.P. Collin, “Terrestrial Optics in an Aquatic Eye: The Sandlance, Limnichthytes fasciatus (Creediidae, Teleostei),” Journal of Comparative Physiology A 177 (1995): 397-408.
- John D. Pettigrew et al., “Convergence of Specialised Behavior, Eye Movements and Visual Optics in the Sandlance (Teleostei) and Chameleon (Reptilia),” Current Biology 9 (1999): R286-88.
- Kerstin A. Fritsches and Justin Marshall, “A New Category of Eye Movements in a Small Fish,” Current Biology 9 (1999): R272-73.
- Pettigrew and Collin, 407.