In those days, the Powers learned that though they could not create new, sapient creatures, they could change mankind into their vision.
In time the powers grew complacent in their duties, the world was a place of infinite interest and the creatures the Creator had placed on it intrigued them. Some of the greater powers thought to try their hands, their own visions for creatures to add to the vast tapestry. Their visions were grand, but the results poor puppets, a mokery of the Creators work. It became apparent, for all their great strength, they lacked something found in the Creator and even in this feeble creation of man, the creative spark that truly made something new. Frustrated they retreated to their strongholds and returned to watching. It seems one of the minor powers had an idea though. He brought some of the man creatures back with him. Playing with them, he tried stretching them out, squishing them down, adding this and that from the other creatures that roamed the land. Then he released his "creations" to see how they would fare. Soon other powers followed his path. The changing had begun, for while the powers could not create a sapient from scratch, they were past masters at changing/adapting to need. The world of man began to shrink so many were being grabbed and twisted into the macabre, changed into new races.