The eukaryotic cell constitutes a new type of cell compared to the prokaryotic one: according to the theory of Lynn Margulis, it derives from the symbiotic association between an archaean and some bacteria. The new cell is able to conquer ecological spaces different from those occupied by Bacteria and Archaea, thanks to two capabilities unknown to the prokaryotes: multicellularity and sexual reproduction. Therefore, new types of organisms evolved, including the first algae, fungi and, towards the end of the Precambrian, the most ancient animals.