The key finding
A 2025 review of comparative endocrinology research reveals that the insulin superfamily is one of the most ancient hormonal systems in animal evolution, with homologous molecules identified in some of Earth’s most primitive animals including sponges and hydra. These organisms emerged hundreds of millions of years before vertebrates evolved pancreases or complex metabolic systems. By tracing insulin’s evolutionary history across the animal kingdom, researchers are uncovering that this molecule’s original function likely differs significantly from its modern role in blood sugar regulation, offering fresh perspectives on why insulin resistance and metabolic syndrome occur in humans today.
What the study looked like
This review paper synthesized findings from comparative endocrinology studies that examined insulin-like molecules across the entire span of animal (metazoan) phylogeny, from the most ancient organisms to modern vertebrates. Rather than conducting new experiments, the author analyzed existing research that identified and characterized insulin superfamily molecules in diverse species ranging from sponges (which lack organs entirely) through hydra (simple organisms with only two cell layers) to complex vertebrates including humans. The analysis focused on both the molecular structure of these hormones across species and their functional roles in different organisms, allowing researchers to reconstruct the likely evolutionary path of this hormone family over hundreds of millions of years.
Why researchers think this happened
The presence of insulin-like molecules in organisms that lack pancreases, circulatory systems, or even complex metabolic processes suggests that insulin’s ancestral function was fundamentally different from glucose regulation. The review proposes that the original role of the insulin superfamily likely involved more basic cellular functions shared across all animal life—possibly cell growth, reproduction, or survival signaling. As animals evolved greater complexity, this ancient signaling system was co-opted and modified for new purposes, eventually specializing in metabolic regulation in vertebrates. The research also highlights how comparative endocrinology has expanded the concept of “hormones” beyond the traditional definition, blurring boundaries between the endocrine, nervous, and immune systems. This broader view suggests that insulin may have originally functioned as a more general signaling molecule before becoming specialized.
How to read this carefully
This review synthesizes findings from multiple studies rather than presenting new experimental data, meaning its conclusions depend on the quality and interpretation of existing research. The identification of “homologous” molecules across vastly different species involves judgments about molecular similarity that can sometimes be debated. Additionally, inferring the “original” function of an ancient molecule requires speculation based on living organisms that have themselves evolved over millions of years—true ancestral organisms no longer exist to study directly. The presence of insulin-like molecules in simple organisms demonstrates evolutionary conservation but doesn’t definitively prove what those molecules originally did. Readers should understand that evolutionary reconstructions involve educated hypotheses based on available evidence rather than definitive conclusions.
What this means for everyday life
Understanding insulin’s deep evolutionary history might eventually reshape how we think about insulin resistance and metabolic syndrome in humans. If insulin originally served broader cellular signaling functions beyond glucose control, the complex interactions we see in metabolic disorders today may reflect this molecule’s ancient, multifaceted role rather than a simple malfunction of sugar regulation. For anyone interested in human health, this perspective suggests that our modern metabolic challenges might stem partly from evolutionary mismatches—our ancient insulin system encountering novel environments (high-sugar diets, sedentary lifestyles) it never evolved to handle. While this doesn’t change current medical approaches, it illustrates how evolutionary biology can provide context for understanding why our bodies respond to modern conditions in particular ways, potentially informing future research directions for metabolic health.