If evolutionists believe all systems generated from the same source why would they deny that Adam & Eve populated the earth?

Not just Christian would not like that, we would not like that too.

Without going into much details because only god knows, Adam was made using mixture of soil from the earth, made into something like clay and stayed for sometime as a hollow object. God later on, put the soul through Adam and that is when he came alive.

So as you can see, God did it in steps (We bielieve God can do anything without needing to do it in steps).
Could this process not be called evolution?

I don't know how we are made, and obviously we cannot block people from investigating and it is normal that people study phenominons. However, denying that Adam & Eve populated the earth with all humans we see today, is something that contradicts the evolution theory itself. if they have not yet identified the complete chain, how would they justify denying in Adam and Eve?