Individuals at the Center of Biology: Rudolf Leuckart’s Polymorphismus der Individuen and the Ongoing Narrative of Parts and Wholes. With an Annotated Translation

Abstract

Rudolf Leuckart's 1851 pamphlet Ueber den Polymorphismus der Individuen (On the polymorphism of individuals) stood at the heart of naturalists' discussions on biological individuals, parts and wholes in mid-nineteenth-century Britain and Europe. Our analysis, which accompanies the first translation of this pamphlet into English, situates Leuckart's contribution to these discussions in two ways. First, we present it as part of a complex conceptual knot involving not only individuality and the understanding of compound organisms, but also the alternation of generations, the division of labor in nature, and the possibility of finding general laws of the organic world. Leuckart's pamphlet is important as a novel attempt to give order to the strands of this knot. It also solved a set of key biological problems in a way that avoided some of the drawbacks of an earlier teleological tradition. Second, we situate the pamphlet within a longer trajectory of inquiry into part-whole relations in biology from the mid-eighteenth century to the present. We argue that biological individuality, along with the problem-complexes with which it engaged, was as central a problem to naturalists before 1859 as evolution, and that Leuckart's contributions to it left a long legacy that persisted well into the twentieth century. As biologists' interests in part-whole relations are once again on the upswing, the longue durée of this problem merits renewed consideration.

Division of labor and recurrent evolution of polymorphisms in a group of colonial animals

“…These concepts coincide with an underlying problem, the nature of biological individuality, and this problem also underlies modern concepts of biological modularity (Elwick 2007;Clarke 2011;Nyhart and Lidgard 2011). In the broad sense (Schlosser and Wagner 2004), ''modular organisms'' are understood primarily as plants and colonial animals whose bodies are formed by iteration of structural morphological units (Jackson et al 1986;Vuorisalo and Tuomi 1986).…”

Ecological developmental biology: environmental signals for normal animal development

“…Certainly, the notion of the “individual” is called into question. The ovum‐to‐ovum definition of a biological individual that is often used today originated with Thomas Huxley (; Nyhard and Lidgard ). As evolutionary developmental biology looks at the changes of development as a function of time, it must take into account the fact that development is not merely the reading out of the genome.…”

Functional innovation through vestigialization in a modular marine invertebrate

“…Since at least the late 18th Century, repetitively budded, polymorphic units in animal colonies have often been seen as different 'individuals' in the sense of compound individuality, with division of labour facilitating the betterment of the colony as a whole (Nyhart & Lidgard, 2011). Nordmann (1840) noted the apparent lack of feeding and digestive organs and observed a bird's-head avicularium rapidly clamp down on a passing nematode, holding it for hours until the worm was eventually torn where it was clamped.…”