We Have Never Been Hosts: Microbial Niche Weaving and the Evolution of Multicellular Life

François Papale, Louis-Patrick Haraoui 

Microorganisms are commonly understood as associates of multicellular hosts: organisms that first exist as biological individuals and are subsequently colonized by microbial communities. Here, we challenge this temporal and ontological ordering by distinguishing microbial presence from microbial influence. Microbial activity can shape biological processes without persistent physical association, through metabolites, environmental transformations, material effects, and ecological processes whose consequences extend across space, time, and generations. We argue that multicellular life evolved and continues to evolve within this longer history of microbial influence. To capture this relational history, we introduce the concept of microbial niche weaving. Drawing on basket weaving, the metaphor emphasizes how relatively stable biological forms emerge through the interlacing of microbial, macrobial, and abiotic relations, without presupposing a pre-existing host, a single weaver, or a predetermined form. We further propose a principle of recursive microbial influence: biological structures and processes shaped by earlier microbial activity can themselves become conditions through which subsequent microbial influence is organized. Examples spanning multicellularity, development, circulation, reproduction, and terrestrialization illustrate how this perspective reframes major evolutionary transitions as reorganizations of pre-existing ecological relations rather than solely as transitions in individuality. Niche weaving does not replace organisms, individuality, symbiosis, or selection as biological concepts, but it changes their explanatory relationship to ecological processes. Hosthood, on this account, is a derived ecological configuration rather than the starting point of host–microbe relations. Multicellular organisms are relatively stabilized patterns emerging within an evolutionary history of microbial influence: in this sense, we have never been hosts.