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After 50,000 Generations, Bacteria Are Still Evolving Greater Fitness

But the increase in fitness never really stopped. The fitness curves workout program were tested to see if it looked like a hyperbola, which approaches but never exceeds a fitness limit, or a power law, in which case fitness will home continue to increase over time even as its pace slows. The results were pretty clear: "the power law outperforms the hyperbolic model with a posterior odds ratio of ~30 million." The team then attempted to build a mathematical model that would describe the fitness increases based on the mutation rate. One of the notable features of their model is that it left out the occurrence of harmful mutations entirely, and it still produced accurate fits to the fitness curves. In other words, evolution seems to be so efficient at getting rid of harmful mutations that they can safely be ignored. Another way this became apparent is the hypermutator strains. Half of the original dozen strains picked up mutations in genes that resulted in further mutations accumulating at a 100-fold higher pace. If negative mutations were much of a problem, then the hypermutators should show fitness curves that were below those of the remaining strains.
Full story: http://arstechnica.com/science/2013/11/after-50000-generations-bacteria-are-still-evolving-greater-fitness/

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