Certain Pokemon only evolve when they are traded with another Trainer. Once traded, evolution will start immediately and the process cannot be stopped. While often an additional condition must be met, such as a certain held item, there are a few Pokemon whom evolve just by being traded:

Graveler	Trade	Golem

Haunter	Trade	Gengar

Kadabra	Trade	Alakazam

Machoke	Trade	Machamp

Boldore	Trade	Gigalith

Gurdurr	Trade	Conkeldurr

Generation V has introduced a new condition involving trading. It involves trading with a specific Pokemon, rather than trading for something random. Only two Pokemon use this method.

Shelmet	Trade for a Karrablast	Accelgor

Karrablast	Trade for a Shelmet	Escavalier

• Also see Items which cause evolution while trading