User:Pbarnes/Fixity of species2

Fixity of species is a term which means all species remained unchanged throughout the history of the earth. This belief was the prominent belief in the western world prior to Charles Darwin work on evolution, the current accepted theory for specie diversity, in the mid-1800s. Most scientists who believed this view did so as an underlying assumption which was not encouraged by type of scientific reasoning. In this sense, these scientist did not actually support this belief system but allowed their ignorance of this topic to mislead their fundamental understanding of diversity. When various alternatives to fixity of species arose (such as Darwinian evolution), some scientist began to outspokenly support fixity of species.

Plato and Theory of Forms
Plato established the philosophy of essentialism which states, objects observed in the real world are reflections of a limited number of essences or eide. Variation is merely the manifestation of imperfect reflections of constant essences. Plato called this the theory of forms. According to Plato, if God was perfect, then all forms of life must have been created. To leave any potential life unrealized would be a violation of the perfection of the highest power (this idea is called the plenitude principle).

Aristotle and The Great Chain of Being
Aristotle is thought to be basis for an idea often called The Great Chain of Being (other names for this same idea are Ladder of Life and Scala Naturae). His idea was that all species could be placed in order, from the "lowest" to the "highest," with worms on the bottom and God 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 or remain fixed. 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 Charles Darwin (and Alfred Wallace) would either never have conceived of evolutionary thought, or would have made no impression when they published their ideas.

Affects on Taxonomy
Carolus Linnaeus, founding father of our current taxonomic system, began his study believing fixity of species. This heavily shaped his work in developing the field of taxonomy. He later rejected the belief after observing interbreeding between various species.

Because of Linnaeus' original belief, fixity of species is sometimes referred to as the "Linnaean Lawn", a metaphor relating which is primarily used in comparison with a phylogenetic tree and a creationist orchard.

Darwin's Early Thought on Species
Many well-known scientist prior to Charles Darwin publications on evolutionary theory have, at one point in their lives believed this view, including Darwin himself. Darwin was raised in a religious family and was a clergyman early in his life. Prior to his studies, he believed the traditional religious view that God created all the species specifically for their environments. After his studies on the Galápagos Islands in which he observed many examples of species which did not remain unchanged as his religious belief suggested. He rejected his belief in fixity of species along with religion all together.

Opponents of Evolution
Other, more stern believers of fixity of species included Louis Agassiz, a zoologist and geologist known primarily for his work on the an ice age hypothesis, and Georges Cuvier, French naturalist and zoologist. Both men directly opposed the evolutionary theory when it was gaining in its popularity.