Evolutions will change the look of the Dumb and make it stronger. Each Dumb has 4 stages of Evolution. The last stage increases its Rarity.
To Evolve a Dumb, you must merge it with the same type of Dumb (same name). You can only merge with a Dumb at the same Evolution stage or lower.
When you evolve a Dumb, the Attack and Vitality of the evolved Dumb will be based on the stats of the Dumbs used plus a certain percentage: 5% if the Dumbs were not at their maximum IQ and 10% if they were. Simply put, it is better to enhance your Dumbs before evolving them.