The full statement is this: In 1859, Charles Darwin wrote, 'The ........................... ...... At the based of the evolutionary tree of all life is AN ORGANISM THAT IS A COMMON ANCESTOR TO ALL LIVING ORGANISMS.
In biology, evolution has to do with gradual but constant changes in the overall form of living organism. Scientists believe that all life forms came from a common ancestor; it is through the process of evolution and natural selection that primitive life forms developed into higher forms of living organisms. In short, what the statement given in the question is trying to say is that ALL LIVING ORGANISMS ARE RELATED BECAUSE THEY HAVE A COMMON ROOT (A COMMON ANCESTOR).