After Darwin's On the Origin of Species, the idea of 'lower animals' representing earlier stages in evolution lingered, as demonstrated in Ernst Haeckel's figure of the human pedigree. In his view, lower animals were simply newcomers on the evolutionary scene. Jean-Baptiste Lamarck envisioned that life is generated in the form of the simplest creatures constantly, and then strive towards complexity and perfection (i.e. Haeckel's Chain of the Animal Ancestors of Man Historical beliefs about the missing link Subsequently, Charles Darwin, Thomas Henry Huxley, and Ernst Haeckel used it in their works with this meaning. 'Missing link' later became a name for transitional fossils, particularly those seen as bridging the gulf between man and animal. The first time it was used as a name for transitional types between different taxa was in 1863, in Lyell's Geological Evidences of the Antiquity of Man. Charles Lyell employed the term a few years later in 1851 in his third edition of Elements of Geology to as a metaphor for the missing gaps in the continuity of the geological column. The earliest publication that explicitly uses the term “missing link” was in 1844 in Vestiges of the Natural History of Creation by Robert Chambers, which uses the term in an evolutionary context relating to gaps in the fossil record. The very idea of an ordering of organisms, even if supposedly fixed, laid the basis for the idea of transmutation of species, for example Charles Darwin's theory of evolution.

Radical thinkers like Jean-Baptiste Lamarck saw a progression of life forms from the simplest creatures striving towards complexity and perfection, a schema accepted by zoologists like Henri de Blainville. 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. It was during the 18th century that the set nature of species and their immutable place in the great chain was questioned. God was at the top of the chain followed by man and then animals. 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. 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. 3 Famous 'missing links' in human evolution.2 Historical beliefs about the missing link.

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