What do humans have in common with single-celled organisms?
Evolution describes the change over time of all living things from a single common ancestor. The “tree of life” illustrates this concept. Every branch represents a species, each connected to other such branches and the rest of tree as a whole. The forks separating one species from another represent the common ancestors shared by these species. In the case of the relatedness of humans and single-celled organisms, a journey along two different paths — one starting at the tip of the human branch, the other starting at the tip of a single-celled organism’s branch — would ultimately lead to a fork near the base of the tree: the common ancestor shared by these two very different types of organisms. This journey would cross countless other forks and branches along the way and span perhaps more than a billion years of evolution, but it demonstrates that even the most disparate creatures are related to one another — that all life is interconnected.
