🌀 nonlinear sciences

External Entropy Production and Human Evolution toward Multi-body Life

This paper theoretically investigates how the emergence of external entropy production through tool use and fire control drove rapid brain expansion and cooperative group formation in early humans, creating a dual entropy production system that offers a thermodynamic perspective on human evolution and global warming.

Original authors: Yasuji Sawada, Kenji Toma

Published 2026-06-18

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Yasuji Sawada, Kenji Toma

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine that for billions of years, life on Earth was like a single, self-contained engine. It took in fuel (food), burned it to keep itself moving, and released heat and waste. In the language of physics, this is called internal entropy production. It's the natural "exhaust" of being alive.

This paper suggests that about 2.5 million years ago, humans started building a second engine outside their bodies. This is what the authors call external entropy production. Instead of just burning fuel inside their own skin, humans began burning fuel in the world around them—first by controlling fire, then by making tools, and eventually by building complex societies.

Here is the story of how that happened, broken down into simple concepts:

1. The Spark: When the Brain Got Big Enough

Think of the human brain as a computer. For a long time, it was running a basic operating system, just enough to survive. But around 2.5 million years ago, something clicked. Archaeological data shows that human brain size suddenly started shooting up, reaching a "critical size" of about 480 cubic centimeters.

The authors suggest this wasn't just random growth. It was the moment the brain became powerful enough to develop self-awareness.

The Analogy: Imagine a group of people trying to move a giant boulder. Alone, they can't do it. But once they realize, "Hey, if we all push together, we can move this," they become a team. That moment of realization is self-awareness.
The Result: Once humans could think, "I am here, and you are there, and we can work together," they started using tools and controlling fire.

2. The Feedback Loop: The Brain and the Tribe

The paper uses math to describe a "dance" between two things: the size of an individual's brain ( $N$ ) and the size of the group they cooperate with ( $S$ ).

Step 1: A slightly bigger brain helps a human understand how to make a tool or control fire.
Step 2: This tool or fire helps the group survive better, allowing the group to grow larger.
Step 3: A larger group creates more pressure and opportunity for individuals to think even harder and develop bigger brains to manage the group.
Step 4: Bigger brains lead to even better tools and larger groups.

It's like a snowball rolling down a hill. The snowball (the brain) gets bigger, which makes it pick up more snow (the group size), which makes it roll faster and get even bigger. The paper argues this "snowball effect" is the engine behind human evolution.

3. The "Second Life": Internal vs. External

The authors propose that humans now live a symbiotic life with two distinct "engines":

The Internal Engine: Your body burning calories to keep your heart beating and cells alive. This has been happening for billions of years.
The External Engine: The collective human activity of burning fossil fuels, running factories, and driving cars. This is the "external entropy production."

The paper claims that the energy humans release into the world through technology is now 2,000 times greater than the energy their bodies burn just to stay alive. We have essentially built a "second life" that exists outside our skin, powered by our collective brains.

4. Why Do We Keep Building? (The "Goal" of Nature)

You might ask, "Why do humans keep inventing new technology? Is it just for comfort?"

The paper offers a surprising answer based on the laws of thermodynamics. It suggests that nature, when it has a system far from equilibrium (like a hot planet), has a "goal": to dissipate energy as fast as possible.

The Metaphor: Imagine a river flowing down a steep mountain. The water wants to get to the bottom as fast as possible. It doesn't "choose" to go fast; it's just the nature of the system.
The Application to Humans: The authors suggest that human technology isn't just a tool for our convenience; it is the method nature uses to dump energy. We are the "valves" nature opened to release energy into the universe. We keep inventing because the "engine" of external entropy production is designed to run faster and faster.

5. The Psychological Conflict

Because we are running two engines at once, the paper suggests this causes a psychological tug-of-war inside us:

The Ancient Instinct: The part of our brain that wants to survive individually (the "Internal Engine").
The Modern Drive: The part of our brain that drives us to build, consume, and expand the group (the "External Engine").

This conflict might explain why we feel a mix of deep-seated instincts and a relentless drive to create technology, even when it causes problems like global warming.

Summary

In short, this paper argues that the moment humans learned to cooperate and control fire, we didn't just evolve as animals; we evolved into a new type of life form. We became a multi-body organism where our collective brain and our technology act as a massive, external engine. This engine is driven by the laws of physics to produce energy waste (entropy) at an ever-increasing rate, and understanding this "second life" is key to understanding why we act the way we do.

Technical Summary: External Entropy Production and Human Evolution toward Multi-body Life

Problem Statement
The paper addresses the thermodynamic evolution of life, specifically focusing on the transition from "internal entropy production" (energy dissipation within a single organism) to "external entropy production" (entropy produced outside the biological body). While the Maximum Entropy Production Principle (MEPP) has been established as a driver for the birth and early evolution of life, the mechanism behind the emergence of external entropy production in Homo sapiens remains theoretically unexplored. The authors investigate the thermodynamic origins of human technological advancement, specifically the use of tools and the control of fire, which have led to energy dissipation rates thousands of times greater than internal biological processes. The central problem is to theoretically model the coupled growth of human brain size (internal world) and cooperative group size (external world) that facilitated this transition.

Methodology
The authors employ a theoretical framework based on non-equilibrium thermodynamics and the MEPP, supported by archaeological data.

Data Analysis: The study utilizes archaeological records of brain volume evolution from chimpanzees to ancient human species (Australopithecus, Homo habilis, Homo erectus, etc.). A critical transition point ( $T_c$ ) is identified at approximately 2.5 million years ago, corresponding to a brain volume ( $N_c$ ) of roughly 480 cc, coinciding with the onset of tool usage and fire control.
Mathematical Modeling: The authors construct a set of coupled nonlinear differential equations to describe the co-development of personal brain size ( $N$ $N$ ) and the size of the interacting human group ( $S$ $S$ ).
- The growth rate of brain size is modeled as a function of the interaction between the individual brain and the group size, minus a natural decay term: $dN/dt = CN(t)S(t) - \gamma N(t)$ .
- The growth rate of the group size is modeled as a function of the brain size, minus a group decay term: $dS/dt = BN(t) - \mu S(t)$ .
- External entropy production ( $P$ ) is defined as proportional to the group size $S$ in the initial phase: $P(t) = AS(t)$.
Linearization: The system is linearized around the critical equilibrium point ( $N_c, S_c$ ) to derive eigenvalues and estimate growth rates. The authors use historical data points to assign numerical values to constants (e.g., decay constants and coupling coefficients) to simulate the growth trajectory.

Key Contributions

Definition of External Entropy Production: The paper formally distinguishes between internal entropy production (biological metabolism) and external entropy production (energy dissipation via tools, fire, and industry), noting that the latter in humans currently exceeds the former by a factor of over 2,000.
Critical Threshold Hypothesis: The authors propose a critical threshold ( $N_c \approx 480$ cc) in brain size required for the emergence of "awareness" (self-awareness). This awareness is posited as the necessary condition for the cooperation required to invent tools and control fire.
Coupled Evolutionary Model: The paper presents a mathematical model linking the expansion of the "internal world" (brain) and the "external world" (cooperative society) through the mechanism of awareness. This model suggests that the birth of external entropy production is a manifestation of the MEPP, analogous to the birth of multicellular life.
Thermodynamic vs. Neo-Darwinian Frameworks: The authors contrast their thermodynamic evolution theory with Neo-Darwinian theory. They argue that while Neo-Darwinism focuses on short-term fitness and genetic mutation, thermodynamic evolution focuses on long-term entropy production maximization in far-from-equilibrium (FFE) systems, offering a consistent explanation for the origin and future trajectory of life and technology.

Results

Growth Rates: The linearized solution yields a growth rate for the system of approximately $\gamma \sim 20$ per million years at the critical point. This aligns with the observed rapid increase in brain size and the subsequent exponential growth of external entropy production.
Coexistence of Mechanisms: The analysis suggests that modern humans exist as a "symbiotic" entity of two life forms: traditional multicellular life (governed by internal entropy production) and "multi-body life" (governed by external entropy production via social cooperation and technology).
Psychological Implications: The coexistence of these two entropy production mechanisms (internal instinct vs. external conscious cooperation) is proposed as a thermodynamic basis for psychological phenomena, including the conflict between individual survival instincts and collective technological advancement.
Nature of Technology: The paper concludes that the continuous growth of technology is not merely a byproduct of human convenience but a thermodynamic imperative driven by the MEPP to maximize entropy production in an FFE environment.

Significance and Claims
The paper claims that understanding the origin of global warming requires an evolutionary perspective based on external entropy production. It suggests that the "second birth" of life—the transition to multi-body life driven by external entropy production—is a fundamental thermodynamic event comparable to the initial birth of life.

Philosophical Impact: The authors argue that this thermodynamic view provides a new perspective on the meaning of self-awareness and technology, moving beyond short-term historical scales (hundreds of years) to evolutionary scales (millions of years).
Practical Application: The paper suggests that a thermodynamic understanding of external entropy production is crucial for developing effective countermeasures against global warming, as the root cause is identified as an evolutionary drive rather than a simple policy failure.
Modesty: The authors acknowledge that the detailed mechanisms of awareness emergence, the specific dependence of coupling constants on brain size, and the precise nonlinear dynamics require further study involving brain science and cultural evolution theory. They do not claim to have solved the psychological problems arising from this duality but propose the thermodynamic framework as a necessary foundation for such research.