Ganymedian

Ganymedians are a sapient species native to Ganymede.

Biology
They are green-haired humanoids which stand about 7 ft (~ 2.1 m) in height but weigh only 150 pounds (~ 68 kg). Their physical strength is only one fifth of the average Human's strength. They're also far more vulnerable to electricity.

Ganymedian brains are divided in two halves, of which only one is actively used. In cases of injury, the dormant half of the brain takes over. However, there is a surgical procedure that can give them the ability to use both halves simultaneously. This operation greatly increases their intellectual capacity at the cost of sharply reducing their accuracy, coordination and eyesight.

Appearances

 * "The Double Minds", by John W. Campbell (1937)
 * "The Immortality Seekers", by John W. Campbell (1937)
 * "The Tenth World", by John W. Campbell (1937)