As simpler animals, and if you look back in time, these again started as even simpler animals. It all started with a molecule that produced copies of itself. If you want to read more details about the start of life you would look up "abiogenesis" and "self synthethising RNA".
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.