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Dual-Coding Genes “Nearly Impossible by Chance” — How Would Francisco Ayala Respond?

We mortals are easily impressed by palindromes — words or phrases that have the same spelling forwards and backwards. But try writing a sentence which has two different meanings: One meaning is gained when you start with one letter of the first word, and then an entirely different meaning is understood when you start reading with the second letter of the first word. Such a sentence would be most impressive, but what if such “sentences” existed in our DNA?

Leading evolutionary biologist Francisco Ayala recently wrote in Proceedings for the National Academy of Sciences (PNAS) that “Chance is an integral part of the evolutionary process.” Ayala then explained why he thinks Darwinian evolution is right and ID is wrong: “Biological evolution differs from a painting or an artifact in that it is not the outcome of preconceived design. The design of organisms is not intelligent but imperfect and, at times, outright dysfunctional.” (“Darwin’s greatest discovery: Design without designer,” PNAS, 104:8567–8573 (May 15, 2007), emphasis added.) This questionable standard and conclusion is Ayala’s punchline against ID.

What, then, does Ayala think of organisms whose design is intelligent and highly functional? A recent article in Public Library of Science discussed how dual-coding genes — genes which overlap and code for multiple proteins when read through different reading frames — are “hallmarks of fascinating biology” and “nearly impossible by chance” to the extent that evolutionary biologists have held “skepticism surrounding” their very existence. Now it seems they do exist, and they don’t quite match Ayala’s vision of biology, where “[c]hance is an integral part” of the “design of organisms is “dysfunctional” and “not intelligent.” As the article, “A First Look at ARFome: Dual-Coding Genes in Mammalian Genomes,” states:

Coding of multiple proteins by overlapping reading frames is not a feature one would associate with eukaryotic genes. Indeed, codependency between codons of overlapping protein-coding regions imposes a unique set of evolutionary constraints, making it a costly arrangement. Yet in cases of tightly coexpressed interacting proteins, dual coding may be advantageous. Here we show that although dual coding is nearly impossible by chance, a number of human transcripts contain overlapping coding regions. Using newly developed statistical techniques, we identified 40 candidate genes with evolutionarily conserved overlapping coding regions. Because our approach is conservative, we expect mammals to possess more dual-coding genes. Our results emphasize that the skepticism surrounding eukaryotic dual coding is unwarranted: rather than being artifacts, overlapping reading frames are often hallmarks of fascinating biology.

(Wen-Yu Chung, Samir Wadhawan, Radek Szklarczyk, Sergei Kosakovsky Pond, Anton Nekrutenko, “A First Look at ARFome: Dual-Coding Genes in Mammalian Genomes,” PLOS Computational Biology, Vol. 3(5) (May, 2007), emphasis added.)

Does this sound like a “dysfunctional” process that is “not intelligent” in its design?


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Francisco Ayala