Dark clones, or also addressed as clone soldiers, were Human male clones created on Kamino since 228 ABY. The order was given by a group of Sith that arrived on Kamino while escaping the Galactic Federation Triumvirate after a tentative of attack against it. The Kaminoans didn't use the accelerated growth with the dark clones, so they would not get old too soon. As a result, the clones have a longer lifespan and receive experince well.