Reading pop history books, you always seem to be able to trace every major civilization to some kind of ancient precursor - Egypt, Babylonians, etc, which themselves developed as a response to invention of agriculture. It only makes sense.
Except Russia. They seemed to just have appeared out of a parallel dimension somewhere after the fall of Rome, already with a developed culture.
What's the deal?
There appears to be a previous thread on their orgins
What's the deal?
The deal is that the debate about Slavic homeland is highly controversial because it is strongly impacted by the political and ideological agendas.
If you want to know the answer to your question I recommend to... wait a couple of years.
To be precise - wait for the results of archaeogenetic investigations that are happening right now or hopefully will be conducted in the near future.