Fig. 14

Cousins are not ancestors, and humans are not descended from chimpanzees. a shows an evolutionary tree of anthropoid primates as it is often depicted, namely as an unbalanced, right-ladderized tree with humans at the extreme end. Viewed in this way, several of the most common fallacies in interpreting trees can arise: for example, that humans are the endpoint of a “main line,” that there is a trend toward “human-ness” from left to right, that the human lineage includes a monkey ancestor, or that there has been no branching in the lineages leading to the other modern species of primates. All are absolutely false. This becomes clearer if a few internal nodes are rotated, as in b, which is an equally accurate depiction of primate relationships. Humans and chimpanzees are more closely related to each other than either is to gorillas, orangutans, or any other living primates. However, note that “chimpanzees,” although depicted as one terminal node here, includes both the common chimpanzee (Pan troglodytes) and the bonobo (Pan paniscus), and if this tree was drawn as recently as 30,000 years ago, it would also include Neanderthals (Homo neanderthalensis) as a sister species to humans. Humans are not descended from chimpanzees any more than chimpanzees are descended from humans; rather, the two share a common ancestor (U) that lived some 5–7 million years ago and that was neither a human nor a chimpanzee. “Monkeys” are divided into Old World and New World lineages. Old World monkeys share a more recent ancestor with apes (Y) than either does with New World monkeys (Z), which means that apes (including humans) and Old World monkeys are equally related to New World monkeys. Monkeys are not ancestral to humans: The two lineages are related as distant cousins, not as grandparents and grandchildren