A Unifying Principle Underlying Social Bonding: Towards a Psycho-Biological Theory

Project Information

BIOBOND

Grant agreement ID: 101116444

DOI

10.3030/101116444

EC signature date 14 November 2023

Start date 1 December 2023

End date 30 November 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 499 875,00

EU contribution

€ 1 499 875,00

Coordinated by

THE HEBREW UNIVERSITY OF JERUSALEM
Israel

Periodic Reporting for period 1 - BIOBOND (A Unifying Principle Underlying Social Bonding: Towards a Psycho-Biological Theory)

Reporting period: 2023-12-01 to 2026-05-31

Summary of the context and overall objectives of the project

Humans are profoundly social, yet most scientific accounts treat social connection mainly as a psychological experience or as a “buffer” against stress. BioBond starts from a different premise: social proximity may change the body in a fundamental way. When we are with a trusted partner, such as a caregiver or romantic partner, our physiology may regulate more efficiently, reducing the bodily “cost” of maintaining homeostasis. If so, social connection is not only emotionally meaningful; it can be biologically beneficial in measurable ways.

BioBond’s overall objective is to test a new framework called Social Physiology: the idea that social interactions can improve the efficiency of core physiological regulation (e.g. metabolic, autonomic, and thermal regulation). The project further proposes a learning mechanism: partners who reliably improve physiological efficiency become preferentially sought and bonded with, because the brain learns who provides the strongest physiological benefit. BioBond therefore aims to provide a mechanistic explanation for how selective bonds form and persist, from infancy through adulthood, and why close relationships are strongly linked to long-term health.

The expected impact is both scientific and societal. Scientifically, BioBond aims to shift social bonding research toward measurable, biological mechanisms that can be compared across physiological systems, ages and species. Societally, understanding how relationships influence metabolic and autonomic regulation could inform strategies to support parents and infants, improve wellbeing, and contribute to prevention frameworks for metabolic and stress-related illness.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the reporting period, we established the empirical and analytic infrastructure needed to study Social Physiology in controlled laboratory settings, across key homeostatic systems in both adults and infants. This included building the capacity to run standardized physiological challenges and to collect high-quality measures across multiple bodily systems.

A key achievement was the development of a new quantitative measure, Social Physiological Gain (SPG), which captures how much the body’s response to a physiological challenge is reduced in social proximity compared to being alone. SPG is designed to be comparable across different physiological systems, enabling a unified way to quantify “social benefit” in homeostatic efficiency.

Using this infrastructure, we implemented protocols and analysis pipelines across three core homeostatic systems:
• Glucose regulation (metabolic responses measured via continuous or plasma-based indices)
• Sympathetic arousal (autonomic activation and recovery assessed via electrodermal measures)
• Thermoregulation (temperature regulation assessed via skin-temperature indices during controlled challenge)

We completed the planned proof-of-concept work for adults across these systems and completed infant testing for sympathetic regulation; infant glucose and thermoregulation are progressing more slowly and remain ongoing. The WP1 work, spanning over 395 human physiology experiments, has been submitted for publication. Building on these results, we are now initiating the next phase designed to test causal predictions of the framework (i.e. whether increasing physiological gains strengthens social preference and bonding).

In parallel, we disseminated and consolidated the project’s theoretical foundation through a peer-reviewed publication that generalizes BioBond’s core logic into a learning framework. Specifically, Cohen & Atzil published “A metabolic framework for reward: Redefining dopamine and opioids as physiological agents” in Neuroscience and Biobehavioral Reviews, on February 2026. The theoretical paper reframes reward as emerging from the metabolic consequences of physiological regulation. This paper formalizes the computational mechanism underlying BioBond’s hypothesis: that physiological efficiency (metabolic gains) can function as a reinforcement signal that shapes what is learned and preferentially sought, including selective social bonding.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A new evolutionary feature of social bonds (Social Physiology). BioBond advances beyond the state of the art by identifying Social Physiology: a cross-domain principle in which physiological homeostasis becomes more efficient in social proximity. While the evolutionary role of sociality through cooperation or threat buffering is well recognized, it has not been directly tested whether social proximity improves core homeostatic regulation in a manner that reduces energetic effort, particularly in systems not traditionally viewed as socially sensitive. Beyond behavioral and ecological advantages, Social Physiology reveals a psycho-biological benefit of sociality that may contribute to the evolution and maintenance of social bonds.

A mechanistic pathway linking bonds to health and longevity. Although strong social ties are widely associated with better health, wellbeing, and longevity, most evidence has been correlational, leaving the physiological mechanisms unclear. BioBond provides a direct, quantifiable demonstration of the immediate homeostatic benefits of social proximity, showing a physiological advantage in glucose metabolism, thermoregulation, and sympathetic activation. Because more efficient regulation in these systems is linked to reduced risk for metabolic and cardiovascular disease, Social Physiology offers a testable mechanism by which social connection may exert health-related benefits by reducing the metabolic effort of homeostasis.

A physiology-grounded account of selective bonding and learning. Existing approaches describe how close relationships are formed and maintained, but they do not fully resolve why social animals are motivated to invest substantial effort and tolerate risks to engage in social interaction when many benefits are long-term. Social Physiology offers an evolutionary solution: immediate physiological gains make social interaction worthwhile in the moment and can accumulate into long-term fitness benefits, aligning proximate motivation with ultimate outcomes. This reframes social animals not as fully autonomous regulators, but as physiologically interdependent organisms.

A cross-system metric and analytic framework (SPG). BioBond introduces Social Physiological Gain (SPG) as a cross-system metric to quantify social enhancement of homeostatic efficiency as continuous, measurable physiological gains with the potential to implement selective bonding. We developed a system-comparable analytic framework and implemented it across distinct homeostatic systems—glucose metabolism, thermoregulation, and sympathetic arousal—enabling a unified test of Social Physiology as a domain-general principle rather than a single-system effect.

A “non-obvious” proof-of-concept in glucose homeostasis. A key breakthrough is demonstrating Social Physiology in glucose homeostasis, a metabolically costly autonomic system not typically conceptualized as socially responsive. Treating glucose regulation as a rigorous proof-of-concept testbed shows that social benefits extend beyond threat buffering or touch and reflect a broader impact on metabolic regulation, with translational implications for pathways linking social connection to metabolic health, including vulnerability to diabetes and related metabolic illness.