Different types of beings in SciFi flix

Had a theory run through my mind very fast but was able to retain a small piece of it. What if the human species is like the batter for all kinds of life and before any changes to our DNA we are just pure vanilla. The stuff in the jars can change each one of us to a secondary life form by a simple modification to our DNA but it effects everyone differently since each human is slightly different. By getting infected with the stuff in the jars someone may become a Xeno, SJ, Engineer or anything else possible. What are your thoughts? Oops forgot to add the main topic, lol Why are humans always the most scared and fragile being in scifi movies. We never come up against something that is small furry and cuddly then destroy them! hahahaha