A holistic world-view which linked all of nature's wonders together into a continuous chain: the inorganic was connected to the organic, the natural world to its omnipotent Creator. The idea was related to ancient concepts of nature's plenitude and continuity — that the universe is filled with all possible forms arranged according to degrees of perfection — but flourished under its familiar name in the eighteenth century. All natural objects were considered ‘chained’ together in a hierarchy according to increasing physical complexity and mental sophistication, from stone pebbles through higher primates and finally God.
Unlike modern evolutionary thought, this was principally a static view of nature. All ‘beings’ were created in what was pictured as a linear, continuous series, and all always remained in their relative position on the chain. However, providing empirical proofs for fine gradations was challenging. Far from seeing smooth continuity in a collection of natural objects, specimens placed next to each other all too frequently revealed ‘gaps’ in the chain, which frustrated naturalists who wanted to find convincing proof of God's perfectly ordered universe.
The search for structures of increasing complexity in nature often led to complications in determining the ‘natural’ hierarchy of specimens. From Aristotle onwards, constructing classification systems had always been predicated on arbitrary judgements, many of which formed the basis of naturalists' debates, and which led some natural philosophers to declare that only individuals, not species, exist in nature. But even looking at individual specimens led to problems in establishing patterns in nature, and many naturalists alternated between thinking of nature as a continuous chain and assuming particular criteria to demarcate groups of species.
For a long time, zoophytes (primitive marine creatures) and shell-carrying molluscs were classic examples of the continuity between minerals, plants, and simple animals. Similarly, certain amphibians could be used as links between sea and terrestrial creatures. Frequently, however, it was difficult to determine where in the natural hierarchy a creature should be placed. The eighteenth-century Swiss naturalist and popularizer of the chain of being, Charles Bonnet, for example, had troubles determining where in the continuum between fish and birds he should place sea lions or flying fish. Further complications in classifying nature's wonders were created by imaginary sightings of monsters and sea creatures such as mermaids, a myth which flourished in the eighteenth century as a result of increased voyages of exploration, and sailors anxious to tell tales of their heroic travels.
While some imagined that creatures might be found to fill gaps between species, others were beginning to find new reasons to suppose discontinuities between animal forms. The early nineteenth-century, influential French comparative anatomist, Georges Cuvier, reconstructed animals based on palaeontological remains, and not only proposed that species were created separately and at different times, but claimed proof from his interpretation of the fossil record that species went extinct. This could not only be taken as a contradiction to the chain of being, according to which no gaps were supposed to exist in nature, but also as offensive to religious belief in a rational and benevolent Creator who would not allow species to die out. In short, the strength of the chain of being was not to be threatened by a weak link.
Perhaps more embarrassing or problematic to the legitimacy of the chain of being was the placement of humans in the scale. A chain that linked all natural objects together by subtle degrees of difference tended to humble humans' estimate of their unique and special position in the world. Humans were generally regarded as residing in the middle of the Great Chain, with angels, spirits, and ‘intellect’ among the ‘links’ to God. While many figured that the upward space between humans and God was infinite, the close proximity of man to beast could be disturbing to theologians. The matter was confounded when, after the ‘discovery’ of African apes, anatomists revealed the similarities between human and animal bodies and brains. Such close ties were exemplified during the eighteenth century in the famous classification system of Carl Linnaeus, who grouped humans with apes in the same order (primates) and even the same genus (homo) as orang-utangs. Linnaeus' designation of humans in the species sapiens, meaning ‘wise, ’ was a gesture toward making man essentially different from animals, and a degree closer to the intelligent beings higher up in the chain.
Even human varieties could be reduced to fine degrees of difference, with a particular person's position in the chain corresponding to a social position. The chain of being could be used as a model to conceptualize different human ‘types’, or races, savages. This led to an apparently ‘natural’ social hierarchy that could then be used to legitimate the development of such programmes as social medicine, evangelical philanthropy, or even colonialism.
— Brian Dolan
