From ScienceDaily:

Over-expressing a gene that lets brain cells communicate just a fraction of a second longer makes a smarter rat, report researchers from the Medical College of Georgia and East China Normal University.

Dubbed Hobbie-J after a smart rat that stars in a Chinese cartoon book, the transgenic rat was able to remember novel objects, such as a toy she played with, three times longer than the average Long Evans female rat, which is considered the smartest rat strain. Hobbie-J was much better at more complex tasks as well, such as remembering which path she last traveled to find a chocolate treat.

One simple modification, three times longer memory plus a problem-solving ability boost. People underestimate the potential value of intelligence enhancement in humans because what they expect are just smarter humans, not humans that are smarter than any human that ever lived. Because the potential range of technological modifications is much larger than the range of natural variations, it’s likely we’ll eventually get smarter-than-human intelligence without even really trying, as long as we try out enough options.