Why we like shellfish

Apparently, at least according to a professor from a state with no coastline, shellfish may have saved the human race at some point in its history when there were no protesters available to lobby world leaders to prevent climate change. 

How shellfish saved the human race

Image courtesy Flickr user avlxyz, via CC

 Yum.  I guess that explains why I like shellfish so much.  How does it explain the existence of people with shellfish allergies though?