 Three major tenets of organicism were particularly congenial to the development of the levels concept. Firstly, the central preoccupation of organicist thought with organization laid down a foundation for levels thinking (cf. Nicholson &amp; Gawne 2015: 364). For the organicists, organization marked the decisive feature for demarcating living phenomena from non-living physico-chemical phenomena (e.g., Woodger 1929: 290–1; von Bertalanffy 1928 [1933: 48]; Needham 1936: ch. 1). Unlike the neovitalists, however, the organicists (particularly during the 1930’s) did not hold organization to be inscrutable, but rather an important explanandum of biological study (Nicholson &amp; Gawne 2015: 365). Moreover, living organisms exhibited a hierarchical ordering among their distinct parts (Woodger 1930: 8; von Bertalanffy 1932: 83; Needham 1936: ch. 5; see also Nicholson &amp; Gawne 2015: 366). This combined nicely with the focus on organization as the major explanandum of biology in that the series of elements that compose different organisms required specific and contextualized treatment. This in turn complemented another main tenet of the organicists, namely the autonomy of biology as a natural science and its phenomena from physico-chemical phenomena (cf. Nicholson &amp; Gawne 2015: 366–7).