Study Suggests that Nonuniversal Genetic Codes May Be Good Designs
here to listen to a podcast that accompanies The Cell’s Design on why the genetic code supports the case for intelligent design.)
The optimization of the genetic code serves as powerful evidence for intelligent design. As a case in point, human engineers labor to make the best designs possible, requiring extensive planning and forethought. Biochemical optimization suggests that the genetic code required intelligent planning and forethought as well.
Still, many evolutionary biologists remain unconvinced that optimization of biochemical systems means that life comes from a Creator. They assert that evolutionary processes fine-tuned the genetic code through an iterative process of variation operated on by the forces of natural selection. These scientists point to so-called nonuniversal genetic codes to support this assertion.
Nonuniversal genetic codes are best understood as deviants of the universal genetic code. Typically, the rules of deviant codes are almost identical to the universal ones, with only a few minor exceptions. Presumably, these alternate codes evolved from the universal code through a microevolutionary process at the biochemical level. Biologists maintain that this evolution means that the universal code could have developed just as well from a non-optimal version to produce the highly optimized universal code.
It’s questionable, however, if the existence of nonuniversal codes actually supports an evolutionary origin of the genetic code. In the late 1960s, Nobel Laureate Francis Crick argued that the genetic code can’t evolve in any substantial way, because if the rules of the code were altered, it would result in a catastrophic condition for the cell.
Even if the genetic code could change gradually over time to yield a set of optimal rules there probably was not enough time for natural selection to discover the highly optimized universal code. (See this article for further discussion on this point.) Natural selection would have to explore 1.40 x 1070 different genetic codes to hit upon the universal genetic code found in nature. If one assumes that there are one billion years available for life to emerge, this evolutionary process would have to evaluate about 1052 codes per second. A search time of ten billion years would necessitate sifting through 1051 codes per second. (The universe is only 13.8 billion years old.)
If the genetic code can’t evolve then how does one account for the nonuniversal codes? I think that these deviants can be explained, in part, as the product of microevolutionary changes. Under highly special circumstances, these changes would allow the code to change rules in an extremely limited capacity. For example, careful study reveals that changes in the nonuniversal genetic codes always occur in relatively small genomes, such as mitochondrial genomes, and involve either: (1) rules that have a minimal, low frequency impact in that particular genome; or (2) rules that tell the cell’s machinery when the information found in DNA comes to an end. Changes in a few specific rules could occur without producing a lethal scenario, since only a small number of proteins in the cell or organelle would experience the potentially harmful effect of the changed rules.
A few weeks ago I pointed out that our creation model allows for optimal designs–once created–to degrade as a consequence of the Second Law of Thermodynamics. It’s possible to understand the nonuniversal genetic codes in these terms. Interestingly, the nonuniversal codes do not display the same degree of optimality as the universal code.
New research, however, indicates that even though deviants are suboptimal and can be accounted for through evolutionary degradation, at least some of them are actually well-designed in other ways–and could reflect what the Creator intended all along. More on this next week.
|Part 1 | Part 2