In evolution there are two kinds, micro and macro. Micro is changes within a species. They are pretty easy to explain ever since Darwin completed his work on natural selection. They cause variety among the same species, like birds and their beaks, or alligators and their lengths.

            Macro is change from one species to another. This is not so easily to explain, actually they’re seems to be no agreement on how it happens, their all ideas that lead to more questions. We rarely see mutations, how can it be that there could have been so many in the beginning of life to cause new species fast?  Maybe Animals could crossbreed and still be able to reproduce, or UV radiation provoked mutations as well as changes in environment.