Professor Lenski revisits a series of experiments on the bacteriophage lambda begun by his lab around 2012.
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.