Minor function change
A minor function change is one which introduces new variants to an existing species. It is, as an approach, less risky than the major change because fewer new sub-assemblies are introduced. This is probably evolution as we have witnessed it. Our species has never seen the major introduction of a completely new species with all of its inherent instability.
The general view seems to be amongst biologists, anthropologists and other scientists in this field that the production of variants is the preferred approach in evolution to the introduction of new species. Again this makes sense. It is far easier to build on a proven design to add function than it is to start again with completely new sets of functions
Most of these changes seem to be triggered by the environment. It is also the major means by which the change is subsequently tested.
It does not actually matter how the extra function is added. As the objective is the overall increase of functionality, then the slight reduction of actual function in a variant in order to add new function is unimportant, as the sum total of functionality is increased. As long as that variant is able to survive for long enough for it to be called a proven design, then it is a success.