Final answer:
The evidence not included for the theory of endosymbiosis is nuclear similarity (option C). Endosymbiosis is supported by the presence of double membranes, DNA similarity, and reproduction techniques of certain organelles, not the nucleus.
Step-by-step explanation:
The question relates to the theory of endosymbiosis, a scientific theory that explains the origin of eukaryotic cells from prokaryotic organisms. The piece of evidence that is not included for supporting the theory of endosymbiosis is c. Nuclear similarity. According to the endosymbiotic theory, organelles like mitochondria and chloroplasts inside eukaryotic cells are thought to have originated from early prokaryotic cells being engulfed by another cell, leading to a symbiotic relationship. These organelles have double membranes, contain their own DNA, and have reproduction techniques similar to bacteria, which support the theory. However, nuclear similarity is not a piece of evidence for endosymbiosis as the eukaryotic nucleus does not show the same evidence of being an engulfed prokaryote like mitochondria or chloroplasts do.