Lenski agrees that the beneficial mutations seen in his Long Term Evolution Experiment are overwhelmingly degradative or loss-of-function ones.
Perhaps the evidence for the vast scope of Darwin’s theory really isn’t as strong as biologists over the years have been telling each other.
Lang and Rice cite a number of articles to show that loss-of-function mutations are just a small minority of those found in studies of organisms.
Their review pretty much completely misses the mark. Nonetheless, it is a good illustration of how sincere-yet-perplexed professional evolutionary biologists view the data.
Professor Lenski’s contrasting of the frequency versus importance of evolutionary changes is misconceived and his illustrations are inapt.