Geological / environmental event
The rising of the savage Isles believed to be the results of all the gods working together to create new land where there before were shallow waters. Indeed many scriptures tell of this event although each god has a different version. Here the gods created many different species. Some in their own image, some to grow strong and dominate the Isles. Common for all is that the gods used this to get more followers which they hoped would result in more power.
With the creation of the Savage Isles many different species were given life. Their first creation were creatures similar to the elves, however these creatures proved far inferior with short lifespans. Each race on the savage Isles claim to be this first creation with everyone else being their copies. However no one knows which came first anymore and even the gods do not answer the question. From here the gods spread out and created many more different species. These species were created by single gods and were often very zealous in their devotion to whatever god created them.