Newly Discovered Example of Convergence Challenges Biological Evolution
“It’s like déjá vu all over again.” This expression, attributed to Hall of Fame catcher Yogi Berra, has become synonymous for something that happens over and over again—and probably shouldn’t.
Evolutionary biologists are confronted with their own form of déjá vu, known as convergence. This term refers to the widespread pattern in nature in which unrelated organisms possess nearly identical anatomical, physiological, behavioral, and biochemical characteristics. The wings of birds and bats represent one textbook example. Birds and bats belong to different groups, with birds assigned to the class Aves and bats to the class Mammalia. According to the evolutionary paradigm, undirected natural processes yielded the identical outcome (wings, in this case) because the forces of selection channeled evolutionary pathways to the same endpoint.
This explanation doesn’t square up, however. If biological systems are the product of evolution, then the same biological systems should not recur throughout nature. Chance governs biological and biochemical evolution at its most fundamental level. Evolutionary pathways consist of a historical sequence of chance genetic changes operated on by natural selection, which, too, consists of chance components. The consequences are profound. If evolutionary events could be repeated, the outcome would be dramatically different every time. The inability of evolutionary processes to retrace the same path makes it highly unlikely that the same biological and biochemical designs should repeatedly appear throughout nature.
The concept of historical contingency embodies this idea and is the theme of Stephen Jay Gould’s book Wonderful Life. To help clarify the concept of historical contingency, Gould uses the metaphor of “replaying life’s tape.” If one were to push the rewind button, erase life’s history, and then let the tape run again, the results would be completely different each time. The very essence of the evolutionary process renders evolutionary outcomes nonrepeatable.
And yet, over the last decade or so, evolutionary biologists have discovered a number of examples of convergence at the organismal and biochemical levels. (For more information, see these articles on convergence and repeated evolution.)
In my most recent book, The Cell’s Design, I document over one hundred examples of convergence at the biochemical level and argue that the widespread occurrence of the multiple repeated origins of a wide range of biochemical systems raises significant questions about the validity of evolutionary explanations for life’s origin and diversity.
Scientists from Purdue University have really uncovered another remarkable example of biochemical convergence in plants. (See here for journal article and here for popular article.) These researchers demonstrated that a specific enzyme (known as a cytochrome P450-dependent monooxygenase) appears—from an evolutionary vantage point— to have independently emerged in two separate instances in lycophytes and angiosperms. This enzyme plays a key role in the synthesis of lignins.
Lycophytes, such as clubmosses, are an ancient lineage of vascular plants that appeared about 420 million years ago. From an evolutionary standpoint, they represent a separate branch from the lineage that produced flowering plants.
All vascular plants make use of a class of large, complex molecules called phenolic lignins in the xylem. The phenolic lignins are polymers. These types of compounds are large molecules comprised of repeating subunit molecules (called monomers.) The different types of vascular plants produce lignins consisting of characteristic subunits. For example, gymnosperms produce lignin made up of guaiacyl monomers. Angiosperms manufacture lignins composed of a mixture of guaiacyl and syringyl monomers. Plant scientists generally regard lignins derived from syringyl monomers as exclusive to angiosperms. This view implies that the enzymes used to make this monomer must have evolved relatively late in evolutionary history when angiosperms appeared on the scene.
Interestingly, there are lycophytes that possess lignins composed of the syringyl monomer. The Purdue researchers determined that the enzyme (ferulic acid/coniferaldehyde/coniferyl alcohol 5-hydroxylase, a cytochrome P450-dependent monooxygenase) that directs metabolites down the pathway that yield syringyl monomers must have evolved independently in lycophytes and angiosperms to yield enzymes that perform identical functions.
Like Yogiisms, this conclusion makes little sense within the evolutionary paradigm, particularly in light of all the other examples of biochemical convergence. It looks as if evolution has repeated itself over and over again—and it shouldn’t have.
Paleontologist J. William Schopf, one of the world’s leading authorities on early life on Earth, has made this very point in the book Life’s Origin.
Because biochemical systems comprise many intricately interlinked pieces, any particular full-blown system can only arise once…Since any complete biochemical system is far too elaborate to have evolved more than once in the history of life, it is safe to assume that microbes of the primal LCA cell line had the same traits that characterize all its present-day descendents.
This pattern, expected by Schopf and other evolutionary biologists, is simply not observed at the biochemical level. An inordinate number of examples of molecular convergence have already been discovered. And undoubtedly more will be uncovered in the future.
Next week I’ll visit the topic of convergence all over again by describing another newly discovered example and discuss how “repeated evolutionary outcomes” provide evidence for the work of a Creator.