How and why Darwin conclude that life stems from common orgins and ancestors?

Darwin discovered through observations of nature that the natural world was not built as-is, as was previously thought, and that species had lived that are now extinct. Eventually he figured out the mechanism by which these changes occur and after that it wasn't a huge leap to look at a horse and then a zebra and a giraffe etc and realize they came ultimately from one ancestor because they have inherited traits which are the same That, in other words, the family tree of life on earth forks If you can see the similarities between a horse and a zebra and a human and another primate, you can see the similarities between all mammals, all animals, and eventually (with modern genetics) all life on earth, including plants, insects and microscopic life.

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.