On the Origins of the Quinarian System of Classification

Abstract

William Sharp Macleay developed the quinarian system of classification in his Horæ Entomologicæ, published in two parts in 1819 and 1821. For two decades, the quinarian system was widely discussed in Britain and influenced such naturalists as Charles Darwin, Richard Owen, and Thomas Huxley. This paper offers the first detailed account of Macleay's development of the quinarian system. Macleay developed his system under the shaping influence of two pressures: (1) the insistence by followers of Linnaeus on developing artificial systems at the expense of the natural system and (2) the apparent tension between the continuity of organic nature and the failure of linear classification schemes (which continuity seemed to require). Against what he perceived as dogmatic indolence on the part of the Linnaeans, Macleay developed a philosophy of science in which hypotheses that exceeded the available evidence should be proposed and subjected to severe tests. He also developed a novel comparative anatomical methodology, the method of variation, to aid in his search for the natural system. Using this method, he developed an intricate system that showed how organic nature could be continuous without being linear. A failure to appreciate these facets of Macleay's thought has led to several misunderstandings of him and his work, most notably that he was an idealist. These misunderstandings are here rebutted.

The living fossil concept: reply to Turner

“…(A generalization of this example is recruited to support Turner's own use of the LF label.) However, the notion of "intermediate form" operative in Darwin's time was more variegated, in part because of competing schemes of classification vying for acceptance, such as Jussieu's natural method or the quinary systems of Macleay and Swainson (Ospovat 1981;Novick 2016Novick , 2019. Textual evidence of Darwin's thinking about the relationship between LFs and anomalous or aberrant morphology reveals both change and ambiguity.…”

Cycles and circulation: a theme in the history of biology and medicine

“…Based on groups of five circles at each taxonomic level, Macleay tried, while avoiding too simple a series, to represent more continuity than Cuvier’s four ‘embranchements’ had allowed. Macleay rejected transformism and the possibility of transitions from one group to the next, but touching circles were intended to show similarities between groups, such as the affinities of cephalopods with molluscs and vertebrates (Novick, 2016 ; see also Van Putten, 2019 on Paul Dietrich Giseke).…”

A “Mean Quarrelsome Spirit:” Controversy in British Systematics, 1822–1836

“…The role of Macleay and his immensely-popular quinarian system in pre-Darwinian natural history has constituted a growing area of interest for scholars in recent decades. Rose Novick has shown that Macleay’s system, far from the quasi-numerological oddity that it has been portrayed as (De Beer 1963 , p. 13; Ghiselin 1969 , p. 104; Blaisdell 1982 , p. 24), in fact provided a sophisticated response to key conceptual issues in the philosophy of classification at the time (Novick 2016 , pp. 110-117).…”

“…Groups are connected by a single point of affinity, represented by an “osculant group” between them, simultaneously preserving natural continuity and accommodating the existence of discrete groups. For a fuller explanation, see Novick ( 2016 ).…”

“…Primary among these were an elevation of the role of analogical relationships and a suggestion that the five members of a quinary group could often be resolved into three. Though Swainson is often considered a “quinarian,” because of his close intellectual kinship with Macleay, it would be more accurate to term his system “circular and trinary.” For this reason, scholars like Novick ( 2016 ) argue that Swainson was not in fact a “quinarian” systematist at all.…”