Evolutionary theory does not say any given species can evolve into totally different species. Evolution is about the accumulation of slight changes in new generations of species.
After scientists and science enthusiasts spent millions on searching the missing link and pouring thousands of manhours into it, eventually, we have discovered that humans have not evolved from existing ape species. It is just that millions of years ago humans and primates were the same species. There has never been a species that linked humans to existing ape species.