A proposed framework for microbial inheritance in mammalian evolution: the apocrine-mammary-microbiota axis
Year: 2026
Type: article
Abstract: Mammalian reproductive and glandular systems provide multiple routes through which maternal microorganisms can be transmitted to offspring, yet the evolutionary significance of these pathways remains incompletely understood. This manuscript proposes that mammalian evolution progressively incorporated microbial transmission into reproductive biology, increasing the fidelity with which beneficial host-associated microorganisms pass between generations. Under this framework, mammary glands evolved from ancestral apocrine-like glands to create sustained maternal–offspring interfaces through which microbial transmission could become an additional selectable function when host–microbe associations enhanced fitness. Comparative evidence from monotremes, marsupials, and eutherian mammals is examined through an apocrine–mammary–microbiota axis, encompassing glandular regulation of epithelial microbial communities, maternal microbial transmission during birth and lactation, and host mechanisms that selectively support microbial establishment. The term filial microorganism is introduced to distinguish microbial lineages whose intergenerational transmission is facilitated by evolved host mechanisms from microorganisms that are merely transmitted through maternal contact or environmental exposure. The framework is further extended, more speculatively, to the eutherian placenta, which is proposed to function not as a resident microbial reservoir but as a transient immunological interface capable of initiating low-abundance microbial founder populations during the physiological transition from pregnancy to birth. Subsequent exposure through the birth canal, maternal skin, glandular secretions, and lactation may then expand and refine these populations during early development. This hypothesis predicts that candidate filial lineages should exhibit preferential maternal transmission, persistence across host generations, evidence of host mechanisms facilitating their maintenance or transfer, and measurable contributions to host fitness. If supported, this framework would broaden mammalian inheritance beyond the transmission of host genes to include evolved biological mechanisms that preserve beneficial microbial partnerships across generations.
Author: Andrew C. Retzinger
Institution: West Virginia University
Language: English
Topic: Gut microbiota and health
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $3,077
OpenAlex ID: W7220428879