Aristotle and the Great Chain


Ideas don't come from thin air. And important ideas like the theory of evolution always come out of the atmosphere of their times. Evolutionary theory was a product of the 19th century, and really couldn't have arisen out of European culture of earlier centuries. Scientists are people before they are scientists, and they are as influenced by the culture and modes of their times as are people of any other professions.

The 19th century was a period when change — progressive change, in particular — was becoming an important expectation. Perhaps surprisingly to the minds of people of the late 20th century, this was a rather new development in cultural expectation.

If we take the beginning of the 19th century as a kind of benchmark, we can say that the broad view of the natural world was largely influenced by a couple of Greek philosophers, and of course by Biblical implications. The Greek philosophers were Plato and Aristotle.

Aristotle

To Aristotle we can attribute the basis for an idea often called "The Great Chain of Being." Other names for the same idea are "Ladder of Life" and "Scala Naturae." This was a try at the development of a kind of classification, or taxonomy. Aristotle was attempting to make sense of the relationships among living things.

His idea was that all species could be placed in order, from the "lowest" to the "highest," with worms on the bottom and you-know-who on the top. In Aristotle's view, the universe was ultimately perfect, and that meant that the Great Chain was also perfect. That meant that there were no empty links in the chain, and no link was represented by more than one species.

This basic concept highly influenced the thinking of centuries of Western civilization. In fact, it still holds a powerful influence over our thinking today. The Great Chain idea places some significant restraints upon the ways we think about species. For instance, if every link is occupied, and none are occupied twice, no species can ever move from one position to another, since to do so would leave one level empty and put two species on another. Thus, in Aristotle's perfect universe, species couldn't ever change. This idea — which today we call the Doctrine of Fixed Species — permeated the western view of species for centuries. In fact, it was the prevailing perspective at the beginning of the 19th century. One of the great cultural changes over that century was the movement away from this restriction in thinking toward a more dynamic view of the natural world. Without this adjustment in thought, it is probable that Darwin (and Wallace) would either never have conceived of evolutionary thought, or would have made no impression when they published their ideas.

Another interesting misconception that arises from Aristotle's notions is that two species must always hold a "higher vs. lower" relationship to each other. This causes us no concern if the two species in question are, for instance, earthworms and human beings. It creates no obvious logical conflict to consider ourselves to be more advanced than Night Crawlers. However, if we consider domestic dogs and cats, the issue is very different. Which is "higher," a dog or a cat? The answer to this question is highly dependent upon the personal perspective of the person you ask. Discuss the issue in a crowded room to demonstrate this to yourself. A piece of advice, though — consider the advantages of body armor before you bring up the question.

This second incorrect notion carries over into our thinking about species and evolution. The problem isn't helped by the fact that biologists often discuss certain features as being "lower" or "higher," or "primitive" or "advanced." The correct uses of these terms should imply nothing further than "older" and "younger" — i. e., earlier vs. later evolutionary appearance. There is no proper implication of "better" vs. "worse," or "more adapted" vs. "less adapted," or "simple" vs. "complex." They certainly don't mean "successful" vs. "unsuccessful." Bacteria are arguably the most successful form of life on Earth.

Our very best evidence indicates that, in reality, all species on this world have equal lengths of evolutionary history. The differences are the result chance differences in the pathways evolutionary movement takes. Evolution is ultimately about diversity, not about progress.


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Updated 25 September 2004