Answer: variations are limited to the confines of lower taxa, since the higher the taxa, the more difficult it becomes to variation to affect them. A group of variations that cause enormous changes into the organisms makes the higher taxas differ from each other.
observable changes from one basic kind into another have never been documented, since this techniques weren't meant to be a part of any researches ongoing. There was no need to analyze in detail what happened to the individuals, and their role was related to nutrition, transportation and even aesthetic purposes.