Figure 1 - Drawings of the nests of (a) a social and (b) a colonial spider, illustrating the differences in the geometry of their webs. (a) Social Anelosimus eximius (Theridiidae). (b) Colonial Philoponella republicana (Uloboridae).
Reproduced from Simon (1891) (public domain).
Abstract
In the origin of multicellular organisms or social groups, a dichotomy emerges between systems where the parts retain some autonomy, referred to as modular, and more integrated unitarian systems. I explore the critical roles of ecology and geometry in determining whether groups form and the degree of integration they develop. I argue that these are essential considerations above and beyond whether groups originate from a single cell or single inseminated female. I consider these points through the lens of social and colonial spiders, which represent early transitions to either unitarian or modular systems. By allowing or constraining cooperation, I suggest that the geometry of their webs—irregular tridimensional versus orbicular—determines the degree of integration of their groups, their scaling properties, their population structure, and their long-term evolutionary fate. Ecology, on the other hand, determines the need or opportunity for groups to form. I extend these lessons to other social systems and levels of organization.