Homologins

Homologins are a term used in speculative biology to describe a proposed class of signaling molecules that emerge from conserved gene families across diverse life forms. In this concept, homologins are small proteins or peptides that retain sequence motifs inherited from ancestral genes and act as intercellular communicators.

Conceptually, homologins link the idea of genetic homology with functional signaling. They are not defined by a single sequence or structure, but by shared heritage and predicted capacity to interact with conserved receptor domains present on many cell types.

Biochemically, homologins are imagined as secreted or membrane-associated entities, often with post-translational modifications that support receptor binding. Their sizes range from short peptides to small proteins, and they typically display recurring motifs that can mediate protein–protein interactions.

Functionally, homologins are hypothesized to regulate development, tissue maintenance, and immune responses by binding to cell-surface receptors and triggering intracellular cascades that influence gene expression. In theoretical models, signaling through homologins can activate commonly conserved pathways, such as mitogen-activated protein kinases or transcription factors.

Empirical support for homologins remains speculative. No consensus definitions or robust experimental validation exist, and some scholars argue that the term conflates orthology with function. Critics emphasize the need for rigorous criteria to distinguish homologins from known cytokines, hormones, or other conserved signaling molecules.

Usage of the term appears mainly in speculative literature, thought experiments, or fictional contexts rather than standard biological databases. As a result, homologins should be understood as a conceptual construct rather than an established scientific category unless future evidence demonstrates conserved function and identity.