Firstly, evolutionary theory is highly possible, bacteria may not be able to reproduce sexually, but they do trade extra chromosomal DNA in the form of plasmids. This is how antimicrobial resistance is conferred.
Bacteria produce what are known as spores, by and large, these are asexual endospores that can be used to protect a bacterium from an unhospitable environment.
It would not be completely out of the question for bacteria at some point to have eventually become a eukaryote or possibly something very close to a eukaryote. Fungi are a good example of of unicellular organisms that have the ability to form complex bodies such as mushrooms. It should also be noted that fungi such as those from the phylum ascomycotia can form spores.
These fungal ascospores can be SEXUAL.
Now when you think about this in terms of a slow continuous process. A cell line from a bacterium, with its primitive DNA repair mechanisms, could easily change over time(with small gradual changes) into something similar to a fungus. These bacteria/fungi could eventually gain the ability to sexually reproduce.
Finally bearing in mind that these INDIVIDUAL cells of fungi can aggregate to form multicellular complex bodies, I would not be suprised that an individual body such as that of a bacterium could eventually produce an animal.
This is just but one path way of evolution to a multicellular complex organism from a unicellular organism.
Endure. In enduring, grow strong.
