"How low can you go?" This familiar call challenges limbo dancers to maneuver their way under a stick held ever closer to the ground. Some biochemists have taken part in a stick dance of their own. Advances in molecular biology make it possible for scientists to take up the challenge of determining "How low can life go?" as they assess life's minimal complexity.
Knowing life's minimal complexity bears directly on origin-of-life models. Evolutionary models require life to be relatively simple in its minimal form. On the other hand, RTB's creation model predicts that minimal life will be inherently complex if it is indeed the work of a Creator.1
One way biochemists measure life's minimal complexity is through the essential gene set-those genes indispensable for life. Knowing the identity and number of such nonnegotiable genes provides understanding of the biochemical processes strictly required for an entity to be recognized as living.
Genes are regions along the DNA molecule that store information the cell's machinery uses to make proteins. Proteins carry out virtually all of life's biochemical activities. For this reason, the essential gene set yields information about the foundational biological operations that are absolutely necessary for life and, hence, serves as a marker for life's minimal complexity.
Molecular biologists have devised a number of methods to identify essential genes. One approach makes use of the bacterium Mycoplasma genitalium. This microbe has the smallest number of genes (482) of any known organism. As a parasite, M. genitalium gets by on relatively few genes because it relies on the biochemistry of the host it infects. Biochemists think that M. genitalium's genome (the sum of its genes) is close to what would be considered the essential gene set. Researchers have learned that by randomly disabling genes from the M. genitalium genome, they can determine which genes are essential by whether or not the microbe dies.
An earlier study published in 1999 estimated the minimal gene set to fall between 265 and 350.2 A recent study making use of a more rigorous methodology estimated the essential number of genes at 382.3
Other researchers have taken a different tack. Instead of using a microbe with a nearly minimal genome, biochemists have studied extremely complex bacteria in an attempt to identify the essential gene set. One recent study worked with Pseudomonas aeruginosa, a microbe with 5,962 known genes.4 As with the M. genitalium studies, researchers randomly disabled genes and concluded that its minimum gene set consists of 335 genes.
Biochemists are finding that whether the stick is initially held high or low, the genetic limbo winds up essentially in the same place. How low can life go? Evidently not much below 380 genes. Life in its bare essence appears to be irreducibly complex, just as RTB's creation model predicts.
- Fazale Rana and Hugh Ross, Origins of Life: Biblical and Evolutionary Models Face Off (Colorado Springs, CO: NavPress, 2004), 43-44.
- Clyde A. Hutchinson, III et al., "Global Transposon Mutagenesis and a Minimal Mycoplasma Genome," Science 286 (1999): 2165-69.
- John I. Glass et al., "Essential Genes of a Minimal Bacterium," Proceedings of the National Academy of Sciences, USA103 (2006): 425-30.
- Nicole T. Liberati et al., "An Ordered, Nonredundant Library of Pseudomonas aeruginosa Strain PA14 Transposon Insertion Mutants," Proceedings of the National Academy of Sciences, USA 103 (2006): 2833-38.