by alecto » June 11th, 2008, 9:14 pm
Richard Lenski scores!
44,000 generations. Six per day, 365 days per year, 20 years. I recreated an experiment like this once, just for 70 generations to see if I could pick up the effect of natural selection. I barely got it. Selection effects dominate for about 1000 generations, when you are basically killing off any bacteria that don't have the right genes to do well under pressure.
Lenski just has the bacteria dealing with their own overpopulation. After a few hours (about 6 generations) the bacteria have reached the carrying capacity of their environment and are starving for the rest of the day, until you take 1 percent out and put them into a brand new beaker with food. I actually added a specific stressor: salinity, and tested for ability to grow in salinity. Lenski is measuring all kinds of changes.
For the next few thousand generations, bacteria change more slowly because of recombination producing more beneficial gene complexes.
Here, at 44,000, they got their first paradigm shift, the creation of a new gene complex. To do this requires multiple steps, which is what they want to go back and look at by analyzing the frozen generations. It's not a "slot machine" where they just got lucky to get the right combinations of genes. There will be a set of intermediate states and a pathway between them - exactly the kind of thing that some (but not all) ID theorists say is impossible.
This experiment involved twelve discrete populations over 20 years. Natural bacteria work in a partly continuous world. Hypotherically, all water bodies are connected so the bacteria are in one "beaker" but because of time of travel constraints, they are not a single population. We're probavly talking about thousands to millions of times the repetitions of Lenski's experiment in space and a hundred million times in time, in order to get the breakthrough of something like photoreceptors. There may be a billion steps, too, a billion useful intermediate forms between rock chewing basic biochemistry and light sensitivity.
This has been one of the most important ongoing experiments, but by itself it certainly does not close any cases. However, it may eke out some general information on the transition of a genome through intermediate states to some important consequence, which may ultimately allow us to estimate the time required for certain changes without resorting to "hand-waving".
Sentio ergo est.