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Apes Relation To Humans

If life is the result of "descent with modification," as Charles Darwin put it, we can try to represent its history as a kind of family tree derived from these morphological and genetic characteristics. The tips of such a tree show organisms that are alive today, and the nodes of the tree denote the common ancestors of all the tips connected to that node; thus all tips that connect to a particular node form a clade. In the diagram on the back, the clade designated by node 2 includes gorillas, humans and chimps. Within that clade the animal with which humans share the most recent common ancestor is the chimpanzee. Humans, chimpanzees, gorillas, orangutans and their extinct ancestors form a family of organisms known as the Hominidae. Most researchers believe from comparisons of anatomy and genetics that the chimpanzee is most closely related to humans like displayed in the diagram.
There are two major classes of evidence that that helps researchers estimate how old a particular clade is: fossil data and comparative data from living organisms. Fossils are normally easy to interpret. By using radiocarbon or thermoluminescence dating techniques the age of the fossil is determined and we then know that an ancestor of the organism in question existed at least that long ago. There are a few good fossils available to compare with the vast biodiversity around us, therefore researchers also consider comparative data, one of   the classes of evidence.

Everyone knows that siblings are more similar to each other than cousins, which reflects the fact that siblings have a more recent common ancestor than do cousins. Analogously, the greater similarity between humans and chimps than between humans and plants is taken as evidence that the last common ancestor of humans and chimps is far more recent than the last common ancestor of humans and plants. Similarity, in this context, refers to morphological features such as eyes and skeletal structure, but unlike fossils one problem...