to the bacteria oxygen was a toxin. The soft membrane bacteria learned to live avoiding oxygen and the hard shelled bacteria created enzymes to prevent damage caused by oxygen. The soft membranoid bacteria learned to group with others of it's same kind and pulled all of it's genetic material into it's center creating the first nucleus and eukaryotic cell. The hard shelled bacteria found a way into the soft bacteria and learned to co-exist. The next step in which the nucleus learned to transfer information to the mitochondria to obtain necessary food led to the cells relationship with it's surrounding environment and began evolution....
