When Theory and Experiment Collide
I've argued that Darwin's mechanism probably isn't powerful enough to produce proteins with fundamentally new structures.  If that's correct it's a serious problem for the old theory, because we know that new protein structures--new folds, as they are known--appeared well over a thousand times in the history of life. If Darwinism doesn't account for these then whatever else it may be, it isn't a complete theory of biological origins.
New protein functions don't always call for completely new structures, though. There are numerous examples of proteins that use very similar structures to perform tasks that are genuinely distinct, meaning that one cannot replace the other. Recognizing this, Ann Gauger and I set out to test how well Darwin's mechanism works on this more modest scale where things that already work are adjusted to work differently.
Read the rest at the Biologic Institute site.