Wesley, the monkey stayed with the giraffes. While we are waiting for him to come back I'm going to explain to you a second factor involved in the evolution : the speciation. For that we are going to help us with our friend the mice.
Firstly the group of the same species of mouse is divided in two differents groups.
Then the different groups are going to different places and change to ajust to the new environment where they live. Finally whereas they are from the same ancestor, the two different groups of mice become two news species and can't have babies together.
Good bye my friend ! See you soon !
Wesley came back with us ! We hope you understand the natural selection and the speciation. Good bye !