Darwin was a great british scientist, he traveled a lot and made famous discoveries. Especially, the theorie of evolution. He published a lot of books. Even if the theory has changed and improved year after year, today's science is based on this theory.
This theory says that humans have a direct link with monkeys and that we change generation after generation. It is totally against what the Bible says and when the theory was published it led to lots of conflicts among society.
Years later.........
MUTATION: changes in the DNA at random. It can have a positive or negative impact on the specie's development. When the change operates on the germinal cells it is transmisible.
NATURAL SELECTION: Heritibles traits as the color of your eyes or your hair (color of the fur here) are better and make it easier for you to survive according to your environment.
GENETIC DRIFT: Sometimes in a small and isolated population several individuals that have the same caracteristics (green blattes) die and only the ones that have the same traits (red blattes) remain(s). So the green blattes disappear little by little and the population in then only composed of the red blattes. The genetic drift is totally random and accidental.
SPECIATION : It's the creation of two news species : When species split up and become two. When two population of one species are geographically isolated they may start to eat or act diferently so their reproduction become impossible. In the end two news species are created.