Convergence Drives Evolution Batty
Chiroptophobia is the fear of bats, but even though they look frightening there is really no rational reason to be afraid of these winged mammals.
There are probably well over 1,000 species of bats in the world, only three of which feed on blood. (All of these blood suckers live in Latin America.) Moreover, relatively few wild bats harbor rabies, probably less than 0.5 percent.
But bats are a cause for concern if you happen to be an evolutionary biologist—so are toothed whales. The multiple, independent origin of echolocation in these animals (twice in bats and once in toothed whales) exemplifies convergence, a phenomenon that describes instances in which unrelated organisms possess nearly identical anatomical and physiological characteristics. When examined from an evolutionary perspective, convergence doesn’t make much sense.
If this wasn’t scary enough, the latest research demonstrates that—again, from an evolutionary perspective—the genetic and biochemical changes that account for the emergence of echolocation in bats and dolphins is identical.1 Given the random nature of the evolutionary process, this recent discovery doesn’t match what evolutionary biologists would expect to find. But both the discovery and convergence make sense if life stems from the work of a Creator.
Echolocation in Bats
Bats belong to the order Chiroptera. Within this order, there are two major groups: Microchiroptera and Megachiroptera. Microbats eat insects and employ echolocation while megabats eat fruit and possess remarkable visual acuity.
As I’ve written previously, evolutionary analysis of mitochondrial DNA sequences indicates that echolocation must have arisen two times independently: once in microbats and once in Rhinolophoidae, a superfamily of megabats. Prior to this discovery, reported in 2000, biologists classified Rhinolophoidae as a microbat based on their capability to echolocate. But DNA evidence indicates that this superfamily has greater affinity to megabats than microbats. This result means that echolocation must have originated separately in the microbats and Rhinolophoidae.2
A couple of years ago, researchers showed, from an evolutionary perspective, that the same genetic and biochemical changes occurred in microbats and megabats to create their echolocating ability. These changes appear to have taken place in the gene Prestin, and in its protein-product, prestin.3
Prestin is a protein associated with the plasma membrane of the outer hair cells, found in the cochlea.4 This protein transports negatively charged chloride and carbonate ions across the membrane, changing the electrical potential across the membrane. This change causes the outer hair cells to lengthen and to stiffen. In this state, the outer hair cells can amplify sound vibrations, passing them on to the inner hair cells.
The outer hair cells of mammals are specially designed to amplify high frequency sound. Among all mammals, the ones with the greatest sensitivity to high frequencies are the echolocating bats and whales.
Echolocation and Convergence
The cochleae of echolocating bats and whales display convergent anatomical features. For example, recent work demonstrates, from an evolutionary view, that the prestin of echolocating bats and of dolphins has undergone the same structural changes.
It appears as if the ability to echolocate occurred independently in three separate instances, twice in bats and once in toothed whales. Evolutionary biologists would say that in all three cases, the evolutionary process converged on the identical anatomical, biochemical, and genetic features in bats and toothed whales.
Evolutionary biologists assert that convergence results when unrelated organisms encounter nearly identical selection forces (e.g., environmental, competitive, and predatory pressures). According to this idea, natural selection then channels the random variations believed to be responsible for evolutionary change along similar pathways to produce similar features in unrelated organisms.
However, this explanation for convergence doesn’t make sense from within the evolutionary paradigm. 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.
Yet this appears to be the case. As evolutionary biologist Simon Conway Morris points out in his book Life’s Solution, convergence is a widespread feature in the biological realm. The remarkable convergence in the echolocating apparatus of bats and dolphins is just one example.
(Go here, here, and here for other examples I have recently written about.)
Convergence and the Case for Intelligent Design
Though the idea of convergence fits awkwardly within the evolutionary framework, it makes perfect sense if a Creator is responsible for life. Instead of convergent features emerging through repeated evolutionary outcomes, they could be understood as reflecting the work of a Divine mind. The repeated origins of biological features equate to the repeated creations by an intelligent Agent who employs a common set of solutions to address a common set of problems facing unrelated organisms.
Not necessarily a comforting conclusion if you suffer from theophobia.
- Yang Liu et al., “Convergent Sequence Evolution between Echolocating Bats and Dolphins,” Current Biology 20, no. 2 (January 26, 2010): R53–R54.
- Emma C. Teeling et al., “Molecular Evidence Regarding the Origin of Echolocation and Flight in Bats,” Nature 403 (January 13, 2000): 188–92.
- Gang Li et al., “The Hearing Gene Prestin Reunites Echolocating Bats,” Proceedings of the National Academy of Sciences, USA 105, no. 37 (September 16, 2008): 13959–64.
- Jing Zheng et al., “Prestin is the Motor Protein of Cochlear Outer Hair Cells,” Nature 405 (May 11, 2000): 149–55.