Missing link (human evolution)

"Missing link" is a hypothetical or recently-discovered transitional fossil. It is often used in popular science and in the media for any new transitional form. The term originated to describe the hypothetical intermediate form in the evolutionary series of anthropoid ancestors to anatomically modern humans (hominization). The term was influenced by the pre-Darwinian evolutionary theory of the Great Chain of Being and the now-outdated notion (orthogenesis) that simple organisms are more primitive than complex organisms. The term "missing link" has been supported by geneticists since evolutionary trees only have data at the tips and nodes of their branches; the rest is inference and not evidence of fossils. However, it has fallen out of favor with anthropologists because it implies the evolutionary process is a linear phenomenon and that forms originate consecutively in a chain. Instead, last common ancestor is preferred since this does not have the connotation of linear evolution, as evolution is a branching process. There is no singular missing link. The scarcity of transitional fossils can be attributed to the incompleteness of the fossil record. The term "missing link" was influenced by the 18th-century Enlightenment thinkers such as Alexander Pope and Jean-Jacques Rousseau who thought of humans as links in the Great Chain of Being, a hierarchical structure of all matter and life. Influenced by Aristotle's theory of higher and lower animals, the Great Chain of Being was created during the Medieval period in Europe and was strongly influenced by religious thought. God was at the top of the chain followed by man and then animals. It was during the 18th century that the set nature of species and their immutable place in the great chain was questioned. The dual nature of the chain, divided yet united, had always allowed for seeing creation as essentially one continuous whole, with the potential for overlap between the links.