That depends if being really smart counts as a mutation. Some circles say yes, others say no.
 
[ Head tipping slightly to the side, he studies the man, trying to figure out what his angle is. Because he sounds awfully at ease with the notion that there are people who have gills.
 
Maybe he's Asgardian. ]
 
What I do have is a means to breathe underwater. Not gills though. See? [ He tilts his head further, showing the video the unblemished line of his neck. ] Fishy free.