Michael Behe writes on June 6th a post entitled: Multiple Mutations Needed for E. Coli. This post came from his amazon blog, where he is trying to push his book. Behe is writing of course about Richard Lenski’s (et al.) recent publication in PNAS (Proceedings of the National Academy of Sciences). In the article, the authors describe an experiment that has been going on since 1988. Now that is persistence! Richard Lenski is the principal author and has kept the same 12 cultures of E. coli reproducing for the last 20 years. These cultures are grown in two food sources: glucose, which E. coli readily uses and citrate, which E. coli cannot use. After nearly 32,000 generations, one of the E. coli cultures developed, or evolved, the ability to use citrate.
This experiment provides an example of a living organism evolving a new trait in the tightly controlled setting. This type of result had not really been seen before (largely due to the long times necessary) and was something of a missing piece of evidence for evolution. Evolutionary type changes have been observed outside of the lab (isolated lizards, nylon eating bacteria), but not in a true experimental setup.
The changes in the isolated cultures of E. coli were not limited to the ability to utilize citrate. They also exhibited changes from the original cultures that include:
higher maximum growth rates on glucose, shorter lag phases upon transfer into fresh medium, reduced peak population densities, and larger average cell sizes relative to their ancestor.
10 of the 12 E. coli cultures also “evolved increased DNA supercoiling.” When challenged with other carbon sources, such as maltose or lactose, their growth rates differed. These changes are indeed important to keep in mind as more evidence of evolutionary change, but the clear advantage of the gain-of-function change illustrated by the new ability to utilize citrate is monumental.
Predictably, Behe does not seem to be too impressed by the experiment. He makes the point that E. coli divides rapidly and 20 years equates to 40,000 (even though the paper clearly states 31,500) generations and therefore is not that remarkable. This may seem like a lot of generations, but 20 years is not even a blink of the eye in evolutionary timescales. I will give an in depth analysis of the numbers in a later post. Besides, this experiment provides proof of concept that random mutations can lead to a gain-of-function change, one of evolution denier’s talking points, as Casey Luskin as said: “ID is far more interested in explaining the GAIN of biological function rather than loss of function.”
Lenski wanted to further explore how the E. coli were able to gain the ability to use citrate. Was it a single mutation event or was it a series of mutations? In order to determine which was true, he repeated the experiment with cultures that had gone through various numbers of generations, 12 in all. He found that when he took cultures after 20,000 generations, they more quickly were cit+. This led Lenski to conclude that there were multiple mutational events leading to cit+, one of which occurred before the 20,000 generation. An important finding, and one that shows that there can be silent, but beneficial, mutations. Behe disagrees:
If the development of many of the features of the cell required multiple mutations during the course of evolution, then the cell is beyond Darwinian explanation.
I am not sure how someone so educated and respected could say something so completely vacuous. In evolution, everything is carried over, whether it has an immediate benefit or not. Maybe one of the mutations that occurred allowed the mutant cell to grow slightly faster than the others. Maybe the mutation was silent and did not help or harm anything. Does Behe really believe that every mutation has to have a large phenotypic effect to be in accord with evolutionary theory?