|MadSci Network: Evolution|
As far as i can tell, the first organisms to evolve in any given environment would be the simplest, unicellular ones. i believe that our biological evolution is driven by our interaction with these microorganisms, and not directly by our own human biological adaption. Thus any given cell type within our bodies would be evolved by infection from these constant & rapidly evolving organisms. We would then be simply the sum total of these, viable or not. We may have stalled our evolution to a point with modern medicine, but not stopped it completely.
Re: Why is biological evolution considered to work top down and not bottom up?
Try the links in the MadSci Library for more information on Evolution.